Case Discussions in Obstetrics & Gynecology Swaraj Batra, YM Mala, Madhavi M Gupta
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OBSTETRICS

Pregnancy with Previous Congenital Disorders1

Sangeeta Gupta,
Sonali Gupta
Fetal congenital disorders are an important cause of prenatal loss and perinatal morbidity and mortality. Congenital disorders can be broadly classified into structural anomalies, aneuploides and genetic disorders. Prenatal diagnosis is the science of identifying structural and functional abnormalities birth defects in the fetus.1 Prenatal diagnosis helps couples to make reproductive choices and the clinicians to provide appropriate counseling and optimize treatment. In the following section, a case based approach to common congenital defects from each catogery will be discussed.
 
NEURAL TUBE DEFECTS
 
CASE 1
Mrs X 30 years old G3+1+0+1+0 with history of both pregnancies affected by neural tube defects (NTD) presented at 8 weeks and 3 days period of gestation. In the first pregnancy patient had conceived spontaneously after one year of marriage and did not seek any antenatal care. Patient delivered at a hospital and anencephaly was detected at birth. However, no comment was made on presence or absence of other anomalies. In the second pregnancy she booked at fifteen weeks pregnancy and had level 2 ultrasound at 19 weeks of gestation. She was diagnosed as occipitomeningomyelocele and opted to terminate the pregnancy. On neonatal review the diagnosis of occipitomeningomyelocele was confirmed and no other gross congenital anomalies were detected. The parents did not consent for postmortem autopsy or chromosomal study.
 
Relevant History
 
Present Pregnancy
  • Gestational age
  • History of exposure to drugs particularly which interfere with folic acid metabolism
  • Any history of hyperthermia and hyperglycemia
  • Intake of folic acid in periconceptional period
  • History of consanguinity.
 
History of Previous Pregnancies
  • Any history of folic acid intake in periconceptional period.
  • History of hyperthermia or hyperglycemia in periconceptional period.
  • History of antifolate drug intake in periconceptional period.2
  • Mode of diagnosis of NTDs (prenatal ultrasound, postnatal diagnosis)
  • Associated malformations and dysmorphisms advisable to switch her to monotherapy in the to delineate genetic disorders preconceptional period and valproate should be
  • Fetal autopsy done or not replaced by lesser teratogenic drugs like phenytoin.
  • Fetal karyotype done or not Time to change the medication is before conception
  • Family history of neural tube defects. as organogenesis is almost complete in the first trimester.
 
Examination
In the first half of pregnancy, there may not be anything remarkable in the examination. However, with advanced gestational age, polyhydramnios may cause increased fundal height and presence of fluid thrill. The presentation of the fetus may be breech or face.
  • Q.1. How will you counsel this woman?
Ans: The woman would be counseled on the issues regarding the risk of recurrence in this pregnancy. The risk of having a baby with neural tube defect in this pregnancy is about 10%.
Anencephaly can be detected as early as 10 weeks of pregnancy and hence she would be advised an early anomaly scan. However, for the defects in the spinal cord patient would be taken up for level II sonography between 18 to 20 weeks of pregnancy.
  • Q.2. If this woman comes in the preconceptional period what counseling should be done?
Ans: She is advised to take high dose of folic acid supplementation (4 mg) starting 3 months prior to conception.
She will be counseled regarding the risk of recurrence of NTD in this pregnancy and early detection of NTDs by ultrasonography is advised.
If the woman is hyperglycemic, then she is referred to a physician for adequate control of her glycemic status before she conceives. If her glycemic status is not known then she would be evaluated with blood sugar fasting and postprandial.
If the woman is on antiepileptic therapy particularly valproate or multidrug therapy, it is advisable to switch her to monotherapy in the preconceptional period and valproate should be replaced by lesser teratogenic drugs like phenytoin. Time to change the medication is before conception as organogenesis is almost complete in the first trimester.
  • Q.3. What are the high risk factors which predispose to neural tube defect in fetus?
Ans: Neural tube defects are example of multi-factorial inheritance. The following factors influence the development of neural tube defects:
  1. Environmental agents like diabetes, obesity, hyperthermia.
  2. Antifolate medications: The antifolate medications implicated in causation of NTD are valproate,2 carbamazepine, coumadin and aminopterin.
    Neural tube defects associated with type 1 diabetes are more likely to be cervical and cervico-thoracic; with valproic exposure lumbosacral defects and with hyperthermia anencephaly.35
  3. Genetic Causes
    • Family history
    • Autosomal recessive condition—Meckel-Gruber syndrome
    • MTHFR gene polymorphism such as C677T and A1298C mutations are associated with hyperhomocystinemia and folate insufficiency is thought to play a role in the phenotypic expression of MTHFR mutations.6
    • Recurrent NTD have been reported to be associated with partial trisomy 2p22 and 20p, resulting from a maternally derived translocation.7,8
  4. Geographical Distribution
    Certain populations in particular geographic areas have increased incidence of NTDs. United Kingdom has the highest frequency of NTD that 3is 1%1. In India, the incidence is 0.5–11 per 1000 births.9
  • Q.4. What is the significance of parental consanguinity in a case of pregnancies with recurrent neural tube defects?
Ans: There is evidence of major gene involvement in familial neural tube defects with parental consanguinity and is likely to be recessive in inheritance. A single gene cause of recurrent NTD is the Meckel-Gruber syndrome. It is a rare autosomal recessive disorder and carries a 25% risk of recurrence. Other features of this syndrome triad include polycystic kidneys and polydactyl.10,11
  • Q.5. What is the recurrence risk for NTDs?
Ans: Recurrence risk with one affected child is 3–4% and after two affected children it is 10%.
The recurrence risk is 4–5% if one parent is affected.
The recurrence risk is 25% when NTD is part of Meckel-Gruber syndrome.
Recurrence risk for first degree relatives of affected children in 1 in 30 and second degree relatives is 1 in 220.12
  • Q.6. What is the role of folic acid supplementation in prevention of neural tube defects?
Ans: There are two aspects in the administration of folic acid supplementation for prevention of NTD- the timing and the dose.2 Pre-conceptional intake of folic acid, beginning 3 months prior to conception in the dose of 400 microgram daily has been recommended for prevention of first occurrence of NTDs and should be continued through the first trimester of pregnancy13,14 However, higher doses of folic acid supplementation (4 mg) are recommended for women at higher risk of NTDs. These include women with prior affected children or if the women or the partner has NTD. In women with previous affected offspring there is 70% reduction in recurrence rate.15,16 Similar doses are used in patients who are diabetic or on antifolate medication but data is limited about their benefit.
  • Q.7. Disruption of folic acid metabolism predisposes to which congenital abnormalities?
Ans: Several congenital abnormalities like neural tube defects, cardiac defects, cleft lip and palate, and even Down syndrome are known to arise, at least in part from disturbance of folic acid metabolic pathways.
  • Q.8. Besides NTD folic acid intake prevents which other congenital malformations?
Ans: Congenital heart diseases and cleft lip and palate are also prevented to certain extent by folic acid intake.17
  • Q.9. What is the screening strategy for neural defects?
Ans: Universal screening of NTDs in antenatal period is recommended as 95% of the cases are seen in the low risk populations.
The screening for open neural tube defects is done by estimation of maternal serum alfa-feto-protein (MSAFP) between 15–20 weeks of pregnancy. The levels are raised in open neural tube defects. Cut-offs between 2 and 2.5 MOMs as upper limits yield detection rates of 100% for anencephaly and 85–94% for open spina bifida. For efficient MSAFP screening determination of accurate gestational age by first trimester scan is important. Other factors which influence MSAFP are maternal weight and ethnicity.
  • Q.10. How are patients with elevated MSAFP evaluated?
Ans: For patients with elevated MSAFP, further testing with targeted ultrasound or amniocentesis is required. Presently, the best approach to evaluate elevated MSAFP is ultrasound.Ultrasound evaluation is done to confirm the gestational age, 4rule out twin pregnancy, fetal demise and identify structural defects that cause elevated MSAFP. Targeted sonographic evaluation for spina bifida in high risk cases has sensitivity of about 97% and specificity of 100%. Amniocentesis for the measurement of amniotic fluid AFP and the detection of acetylcholinesterase (AChE) has been replaced by ultrasonography.
When no fetal abnormality is detected, MSAFP elevation may be associated with adverse pregnancy outcomes like fetal growth restriction, oligohydramnios, placental abruption, preterm membrane rupture, preterm birth and even fetal death.18 However, optimal management is unclear and prenatal care for these women is not altered unless specific complication arises.
  • Q.11. What are the causes of raised MSAFP?
Ans: In 50% of cases, incorrect dating will be identified and adjustment of initial value resolves the issue.
Fetal demise is also associated with raised MSAFP.
The various structural defects associated with raised MSAFP are open neural tube defects, fetal abdominal defects such as omphalocele and gastroschisis, sacrococcygeal teratoma, fetal urinary tract obstructions and urinal atresia.
  • Q.12. What are the causes of low MSAFP?
Ans: Obesity, diabetes, chromosomal trisomies, gestational trophoblastic disease, fetal death, overestimated gestational age.
  • Q.13. What are the sonographic features in various neural tube defects?
Ans: The antennal diagnosis of anencephaly is based on absence of fetal calvaria.
Anencephaly can be identified by ultrasound as early as 10 weeks of gestation but should be reconfirmed by a scan at around 13 weeks because ossification of the skull in some cases may not be completed until that time.19
Ultrasound diagnosis of meningomylocele is frequently based on a cystic mass protruding from the dorsal vertebral bodies without skin covering. This is ideally seen in the transverse plane as a wide separation of the lateral processes of lamina (Fig. 1.1).
Indirect sonographic signs of meningomylocele have been found to be as important as visualization of the spinal lesion and are somewhat easier to image. These include ventriculomegaly, microcephaly, frontal bone scalloping (lemon sign) (Fig. 1.2), and obliteration of the cisterna magna with either an absent cerebellum or abnormal anterior curvature of the cerebellar hemispheres (banana sign)20 (Fig. 1.3). Banana and lemon sign are produced by caudal displacement of cerebellar vermis, fourth ventricle and medulla constituting the Arnold-Chiari II malformation. These findings are seen in over 95% of cases of neural tube defects in the middle of the second trimester. The banana sign and the lemon sign may not be present after 22 to 24 weeks' gestation.
The presence of neural tissue in the meningeal sac and level and length of the lesion should be ascertained on sonography to predict the extend and severity of the neurological deficits.
zoom view
Fig. 1.1: Axial view of spina bifida
5
zoom view
Fig. 1.2: Lemon sign
zoom view
Fig. 1.3: Banana sign
Besides the detailed evaluation of the cranium and spine, comprehensive ultrasound examination should be performed to exclude genetic syndromes.
  • Q.14. When does neural tube close in the embryo?
Ans: Neural tube closure occurs in the 3rd to 4th week after fertilization.21 Closure in the region of the developing head and sacrum is completed approximately 24 and 26 days after conception, respectively.
  • Q.15. How will you counsel and manage the couple if anencephaly is detected?
Ans: Anencephaly is lethal and can be diagnosed accurately by antenatal ultrasound.
In our country termination of pregnancy can be offered till 20 weeks of gestation as per the PNDT act. Fetal autopsy should be offered for all fetuses with anencephaly to detect other anomalies as it may form a part of genetic syndrome and helps in predicting the recurrence risk.
In recurrent NTDs fetal and parental karyotyping could be useful in the future management since partial trisomies are the implicated cause.22
However, couples who refuse termination are followed up with routine antenatal care. The woman is more likely to have complications like polyhydramnios, malpresentation (face, breech) and postmaturity. Polyhydramnios, may result from diminished fetal swallowing, secretion of cerebrospinal fluid directly into the amniotic cavity and excessive micturition. Postmaturity is a consequence of absent or hypoplastic pituitary gland.
During labor, shoulder dystocia and obstructed labor should be anticipated.
  • Q.16. How will you counsel the patient if meningomyelocele is detected?
Ans: Patient should be counseled regarding the prognosis which depends on the presence of neural tissue in the meningeal sac and spinal level and length of the lesion. The spinal cord below the lesion is dysplastic and lower limb paralysis and incontinence of bowel and bladder is common. Intelligence may be affected from either the lesion itself or the impact of treatment (shunt placement). Early closure of the defect and ventriculoperitoneal shunting of any associated hydrocephalus should be performed.23,246
The option of pregnancy termination should be included in counseling if the gestational age is less than 20 weeks.
If patient plans to continue the pregnancy, a multidisciplinary team consisting of a pediatric neurologist, neurosurgeon, obstetrician, and neonatologist should manage the patient to optimize the neonatal outcome and plan surgical management.
In utero surgical repair of NTDs is still in experimental phase and currently there is insufficient data to judge the benefits and risk of this approach.25
 
DOWN'S SYNDROME
 
CASE 2
Mrs B, 24 years old had a previous baby with Down syndrome one year old.
 
History
  • Age of the mother at delivery
  • Period of gestation at which the pregnancy was registered
  • First trimester scan for nuchal translucency
  • Whether first or second trimester screening was done
  • Second trimester anomaly scan
  • Pregnancy outcome: Miscarriage, stillborn or live born
  • Obstetrical history: P1+0+0+1
Her first pregnancy was a spontaneous conception. She sought antenatal care at 20 weeks of pregnancy. She had a term delivery at a hospital of a small for gestational age baby. The baby had mongoloid facies and a ventricular septal defect was diagnosed. The baby had delayed milestones and on investigations the baby was diagnosed with Trisomy 21.
Case: The woman is desirous of further child-bearing but is apprehensive about similar problem in the next baby and has come for preconceptional counseling. The karyotype of the effected child showed Trisomy 21 (47,XY).
  • Q.17. What recurrence risk would you attribute to this lady?
Ans: Down's syndrome cases result from nondisjunction, translocation or mosaic.
With a pregnancy complicated by trisomy 21 from nondisjunction, the woman has 1% risk of having a pregnancy with trisomy in subsequent pregnancy. This risk pertains unless her age related risk exceeds it.
Because of this risk, she would be offered invasive prenatal diagnosis.
Parental karyotype is not indicated in this couple.
  • Q.18. What is the incidence of Down syndrome in general population?
Ans: Down's syndrome occurs in 1 in 800 to 1 in 1000 newborns.26
  • Q.19. What are the different cytogenetic mechanisms associated with Down syndrome?
Ans: Chromosomal abnormalities in Down syndrome.27
Abnormality
Frequency (%)
Trisomy
95
Translocation
4
Mosaic
1
Ninety-five percent of Down syndrome cases have primary trisomy of chromosome 21(47 instead of normal 46). These cases show the well-known relationship to maternal age. Ninety-five percent of trisomy children inherit their additional chromosome as a result of nondisjunction of maternal gametes while only 5% are paternally derived.28
Four percent of Down syndrome cases have Robertsonian or unbalanced translocation. By contrast, translocations show no definite relationship to parental age and may be either sporadic (two third) or familial (one third).28 The familial translocations carry greater risk of recurrence for future offspring.7
Children with mosaicism are often less severely affected than in the full syndrome.
  • Q.20. What recurrence risk is attributed for Down syndrome with unbalanced or Robertsonian translocation?
Ans: If a child has down syndrome as a result of de novo translocation, that is neither parent will have a balanced translocation, the likelihood of Down syndrome offspring's recurring in such a couple is 0.5 to 1%.
However, if either of the parents harbors balanced translocation, the risk of recurrence exists. For female carriers of Robertsonian 14;21 translocation, the risk of having a liveborn infant with Down syndrome is approximately 10%. The risk is approximately 1% for a male carrier.29,30 When parental translocations involve homologous chromosomes, that is 21, 21 possibility of a normal liveborn infant is precluded. For such couples, donor gametes should be considered.
  • Q.21. What is the indication of parental karyotype in cases of Down syndrome?
Ans: When a fetus or child is found to have a translocation trisomy, chromosomal studies of both parents should be performed. If neither parent is a carrier and the translocation occurred spontaneously, the recurrence risk is extremely low.26 In one third cases one parent will be a carrier. Other relatives can also be carriers and efforts should be made to identify all adult translocation carriers in a family so that they can be alerted to possible risks to future offspring. This is sometimes referred to as translocation tracing or chasing.28
  • Q.22. What is the risk of Down syndrome in offspring of parents with Down syndrome?
Ans: Females with Down syndrome are fertile and a third of their offspring will have Down syndrome. Males with Down syndrome have markedly decreased spermatogenesis and are almost always sterile. The risk of a chromosomally normal fetus having a birth defect or mentally handicapped could be as high as 30%.31
  • Q.23. What is the fetal death rate with trisomy 21?
Ans: With trisomy 21, the fetal death rate is about 30% between 12 and 40 weeks, and about 20% between 16 and 40 weeks.32
  • Q.24. What is the significance of parental aging in Down syndrome?
Ans: There is well documented association between advancing maternal age and nondisjunction trisomy 21. The most favored explanation is an aging effect on the primary oocyte which can remain in a state of suspended inactivity. Paternal age has no association with Down's syndrome though in nondisjunction, in 5% children the extra chromosome is paternally derived. The parental age has no bearing in the Down syndrome due to translocations.33
Maternal age at delivery (in years)
Risk of Down syndrome
20
1 in 1500
25
1 in 1350
30
1 in 900
35
1 in 400
37
1 in 250
40
1 in 100
45
1 in 30
Case: The woman in the above scenario reports to you at 8 weeks pregnancy.
  • Q.25. What is your plan of management in the current pregnancy?
Ans: Since the recurrence in this pregnancy is about 1%, the women will be directly offered invasive testing with chorionic villous sampling to ascertain the chromosomal configuration of the fetus. In such patients there is no role of serum screening or combined screening. If she reports later than 14 8weeks she is offered prenatal diagnosis with amniocentesis.
  • Q.26. What are the indications of invasive prenatal testing?
Ans:
  1. Maternal age > 35 years
  2. Previous offspring with aneuploidy.
  3. Multiple or major congenital malformations on ultrasonography
  4. Positive screening test.
  5. Parental aneuploidy.
  6. Intracytoplasmic sperm injection: there is increased risk of (1%) sex chromosomal abnormalities in pregnancies established by ICSI.
  7. Recurrent spontaneous miscarriages.
  8. Family history of single gene defects.
  9. Structural chromosomal rearrangements.
    1. Either parent with Robertsonian translocations
    2. Parental reciprocal translocations: mode of ascertainment is very important. If a balanced reciprocal translocation is ascertained through an unbalanced child or another liveborn relative, the likelihood of unbalanced liveborns is approximately 20%. If balanced translocation is ascertained through a history of repeated miscarriage, the risk for an abnormal liveborn is much lower (1–5%).34
Case 3: A 28 years old primigravida comes to your antenatal clinic at 10 weeks pregnancy for routine antenatal care. The woman is offered prenatal screening for aneuploides.
  • Q.27. What options are available for the woman?
Ans: The options available for the woman along with their detection rates are as per Table 1.1.35
It is very important to remember that whichever method is chosen for screening, determination of correct gestational age by ultrasonography is mandatory for correct risk assessment.
The maternal age is another important determinant of risk estimate as discussed earlier that increasing maternal age predisposes to a higher risk for aneuploides. Thus, it forms an integral part of any screening test. Patient's weight, diabetic status, ethinicity and smoking should be taken into account as they have bearing on serum markers level.
Case: A 28-year-old primigravida on Ist trimester combined screening is found to have a high risk of trisomy 21 (1:80).
Table 1.1   Options available for prenatal screening for aneuploides along with their detection rates
Methods of screening
Detection rate (%)
False positive
Maternal age
30%
5%
Maternal age and triple test at 15–18 weeks (alpha fetoprotein, free beta-hCG, uE3)
50–70
5%
Maternal age and quad test at 15–18 weeks (alpha fetoprotein, free beta-hCG, uE3, inhibin-A)36,37
80%
5%
Maternal age and nuchal translucency (NT) at 11–13 weeks
70–80%
5%
Maternal age and fetal NT and maternal serum free beta-hCG and PAPP-A at 11–13 weeks
85–90%
5%
Maternal age and fetal NT and nasal bone and maternal serum free beta-hCG and PAPP-aat 11–13 weeks
95%
5%
Serum integrated- PAPP-A in first trimester and Quad test in second trimester38
85%
5%
Fully integrated- PAPP-A and NT in first trimester and Quad in second trimester)
85–90%
1–2%
9
zoom view
Flow chart 1.1: Management of the woman with normal karyotype and NT >3 mm
  • Q.28. What will be the future course of management including patient counseling?
Ans: A cut off of more than or equal to 1 in 250 is classified into high risk group. Hence, all patients with risk more than 1 in 250 should be offered invasive testing. Definitive diagnosis is established by invasive testing only.
The invasive tests available are chorionic villous sampling between 11 to 14 weeks and amnio-centeses between 15 to 20 weeks. The advantages, disadvantages and complications of each test should be discussed with the couple.
If the result of the karyotype is abnormal, the couple has the option to terminate or continue the pregnancy. The methods of termination of pregnancy available at various gestational ages and their complications should also be discussed.
  • Q.29. How will you manage this woman if on chorionic villous biopsy the karyotype is normal but the NT is 4 mm?
Ans: In this woman, since the nuchal translucency (NT) was more than 3 mm and the karyotype is normal, the protocol is followed as per Flow chart 1.1.
  • Q.30. What are the inferences drawn from NT evaluation? Do you think cystic hygroma confers a different risk estimate?
Ans: The prevelance of fetal abnormalities and adverse pregnancy outcome increases exponentially with NT thickness. However, the parents can be reassured that the chances of delivering a baby with no major abnormalities is more than 90% if the fetal NT is between the 95th and 99th centiles, about 1070% for NT of 3.5–4.4 mm, 50% for NT 4.5–5.4 mm, 30% for NT of 5.5–6.4 mm and 15% for NT of 6.5 mm or more.39
Increased fetal NT thickness at 11–13 weeks is a common phenotypic expression of chromosomal defects and a wide range of fetal malformations and genetic syndromes.
Increased NT is associated with40
  1. Aneuploidy
  2. Major cardiac defects
  3. Diaphragmatic hernia
  4. Omphalocele
  5. Body stalk anomaly
  6. Skeletal defects
  7. Fetal akinesia deformation sequence
  8. Noonan syndrome
  9. Smith-Lemli-Opitz syndrome
  10. Spinal muscular atrophy
First trimester cystic hygroma has the strongest prenatal association with aneuploidy with significantly worse outcome compared with simple increased nuchal translucency.41
In about 75% of fetuses with cystic hygroma, there is a chromosomal abnormality and in majority of cases, the abnormality is Turner syndrome.
  • Q.31. What is pathophysiology associated with increased NT?
Ans: The following mechanisms are implicated in the pathophysiology of increased NT:39
  1. Cardiac dysfunction
  2. Venous congestion in the head and neck
  3. Altered composition of the extracellular matrix
  4. Failure of lymphatic drainage
  5. Fetal anemia
  6. Fetal hypoproteinemia
  7. Fetal infection
  • Q.32. What is the role of second trimester sonography in risk estimation of aneuploidy?
Ans: If the second trimester scan demonstrates major abnormalities like congenital heart disease, diaphragmatic hernia, omphalocele, it is advisable to offer fetal karyotyping, even if these abnormalities are apparently isolated, as chances of associated aneuploidy are high.42
If the abnormalities are either lethal or they are associated with severe handicap, such as holoprosencephaly, fetal karyotyping constitutes one of a series of investigations to determine the possible cause and thus the risk of recurrence.
Genetic sonography refers to systematic use of composite of diverse mid trimester markers to estimate the risk of Down syndrome. This screening was developed and has been found to be of value in high risk population. The highest yield is achieved with the combination of serum and ultrasound screening in the general population. Various studies have revealed low diagnostic sensitivity for mid trimester ultrasound screening in low risk population. The composite rather than isolated sonographic markers are the current paradigm for sonography based down syndrome risk estimation.
  • Genetic sonogram should be an option for women with advanced maternal age even if their serum screen results are normal, as few additional fetuses with Down syndrome could be identified. For those patients who have a normal genetic sonogram and a normal maternal serum screening results, the risk of trisomy 21 is very low and probably does not warrant invasive testing.43 Seuter and coworker demonstrated that serum screening and the genetic sonogram were largely independent of each other and therefore, could be used as independent modifiers of the risk of Down syndrome.44
  • Minor fetal abnormalities or soft markers like nuchal thickness, middle phalanx, sandal gap, echogenic bowel, echogenic cardiac focus, short femur, short humerus are common and they are not usually associated with any handicap, unless there is an underlying chromosomal defect.11
  • Q.33. What are the new advances in noninvasive diagnosis of Down syndrome?
Ans: With the use of chromosome- specific DNA probes and fluorescent in situ hybridization (FISH) it is possible to suspect fetal trisomy by the presence of three-signal nuclei in some of the cells of the maternal blood enriched for fetal cells. There is evidence that increased level of cell free fetal DNA is present in trisomy 21 pregnancies. However, this method is more likely to find an application as a method for assessment of risk, rather than the noninvasive prenatal diagnosis of chromosomal defects.45,46
Beta Thalassemia
Beta thalassemia is the most common single gene disorder in our country. Carrier frequency varies from 3–17% in different populations. The most effective approach to reduce the burden of the society and reduce the disease incidence is implementation of a carrier screening program, offering genetic counseling, prenatal diagnosis and selective termination of affected fetuses.
  • Q.34. What are various variants of β thalassemia?
Ans: β thalassemia is characterized by diminished production of β globin chains which causes unmatched α globin chains to accumulate and aggregate. The deficiency of β globin synthesis may be compensated partially by an increase in δ and γ chain synthesis. This leads to increased levels of HbA2 (α2, δ2) and HbF (β2, γ2) on hemoglobin electrophoresis. β thalassemia has three major clinically important syndromes. β thalassemia minor, β thalassemia major and β thalassemia intermedia.
β Thalassemia Minor
Patients who have β thalassemia minor are heterozygous for β globin mutation. They have mild sor no anemia. Peripheral smear shows hyperchromia and microcytosis with basophilic stippling.
HbA2 and HbF levels are increased.
Unlike iron deficiency anemia, it is characterized by normal to increased proliferation of RBCs.
β Thalassemia Major
Results from homozygous or double heterozygous mutations in the β globin gene.
In β0 thalassemia, the most severe form, no β globin chains are synthesized. Only HbA2 and HbF are found on electrophoresis.
When small amount of β globin chains are synthesized, the condition is called β+ thalassemia. HbA2, HbF and HbA are found on electrophoresis. It is milder than β0 thalassemia.
β Thalassemia Intermedia
These patients carry two β thalassemia mutations but present with symptoms later in life and have milder anemia than patients who have β thalassemia major. They are not transfusion dependent but may require transfusions periodically. Despite the low transfusion rate, iron overload occurs in these patients as a result of increased intestinal absorption of iron that is caused by ineffective erythropoiesis. The complications of iron overload present later but may be as severe as those seen in patients who have β thalassemia major.
  • Q.35. How will you screen for thalassemia in pregnancy?
Ans: Screening is offered to the women if she is identified as belonging to an ethic population whose members are at higher risk of being carriers. Ideally screening should be done preconceptionally or as early as possible in the pregnancy.
  1. The preliminary screening method for all forms of thalassemia relies on hematologic index 12cutoffs, which involves an accurate blood count using an electronic cell counter. Individuals with mean corpuscular volume (MCV) < 80fl and mean corpuscular hemoglobin (MCH) < 27pg should be further examined to confirm or exclude the diagnosis of β thalassemia. This, however, requires an expensive electronic blood cell counting apparatus and cannot be applied in rural areas where laboratory facilities and economic resources are limited.47
  2. A cheaper, rapid, simple and cost effective alternative for screening is NESTROF (naked eye single tube red cell osmotic fragility test).
Principle: It is based on the limit of hypotonicity which the red blood cells can withstand.
Method: 2 ml of 0.36% buffered saline solution is taken, 0.02 ml of patient's blood is added to it and allowed to stand for 20 minutes.
After 20 minutes reading is taken on a NESTROF stand on which thin black line is marked.
Interpretation: If the line is visible through the solution the test is taken as negative and if the line is not visible, the test is positive.
In β thalassemia trait cases, black line is not clearly visible since microcytic hypochromic red cells of thalassemia trait are more resistant to lysis than normal normocytic normochromic red cells.
Limitations: other conditions which give positive result are:
  • Iron deficiency anemia
  • Hb E thalassemia
  • Hb D thalassemia
NESTROF has sensitivity ranging from 94–99%.
NESTROF has been recommended for the mass screening due to its low cost, simplicity and high negative predictive value.
Combination of NESTROF and red cell indices increases the sensitivity and negative predictive value to almost 100%.
The finding of any abnormality (low MCV, low MCH, abnormal hemoglobin electrophoresis) requires screening of the partner.
  • Q.36. How will you proceed if screening tests are positive?
Ans: Raised HbA2 level is the gold standard for the diagnosis of thalassemic trait. The definitive test for β thalassemia status is HbA2 of >3.5%.
Next step is hemoglobin electrophoresis or HPLC (High performance liquid chromatography) for the quantification of HbA2 and HbF.
 
Hemoglobin Typing
HbA (96–99%) + HbA2 (2–3.5%),
Normal
MCV normal
HbA (92–96%) + HbA2 (>3.5%),
β-thal trait
MCV < 80fl
HbA (96–99%) + HbA2 (<3.5%),
Iron deficiency
MCV < 80 fL
anemia
HbA (0–0.4%/2.1–10.6%),
Thalassemia major
HbA2 (4–10%), HbF (>90%)
0+).
Case: Mrs Y 24 yr old G2P1L0 presented at 8 weeks of gestation
O/H: She had mild anemia during the pregnancy. Previous child had history of repeated blood transfusions with delayed milestones and died at 5 year of age because of heart failure.
Past history: No history of blood transfusions in the woman.
  • Q.37. What is your provisional diagnosis?
Ans: Couple may be a thalassemia carrier
  • Q.38. How will you confirm the diagnosis?
Ans: The carrier status of the couple is confirmed by performing HPLC on both the partners.13
Mr. X, 29 years
Clinical Pathology LNH B-THAL Short Program
REPORT 23-3-10
ANALYTE ID…………………..
%
F…………………………..
5.5
P2………………..
4.0
P3………………..
3.6
A0………………..
79.9
A2………………..
5.6
Mrs. X, 25 years
ANALYTE ID…………………..
%
F…………………………..
0.0
P2………………..
4.7
P3………………..
3.6
A0………………..
85.7
A2………………..
6.3
Unknown I……………………
0.3
In this case, the HbA2 of both the partners was more than 3.5% and hence diagnosed as β-thalassemia traits.
  • Q.39. What is the risk of transmission to the fetus in this couple?
Ans: Since both the partners are found to be carriers, they should be referred for genetic counseling.
It is single gene disorder and has autosomal recessive pattern of inheritance. Since both parents are carrier there are 25% chances for thalassemia major, 50% chances for thalassemia trait and 25% chances that baby will be normal.47
To offer the prenatal diagnosis to the couple it is essential to characterize the DNA mutations of the parent.48 The β thalassemias are extremely heterozygous at the gene level, more than 200 mutations have been described from different parts of the world. The mutations are distributed geographically so that for a given high risk population, there are only 4 to 10 dominant mutations. Therefore, the general approach to the molecular diagnosis of β thalassemia is to identify and test for the region specific mutations based on the patient's ethnic background. This approach identifies the mutation in more than 90% of the cases. If the mutation is not identified, screening for the broader range of mutations is performed.
Studies conducted in India have identified about 28 mutations in Indian population. Generally, when both the partners are carriers, their DNA is studied for 5 common and 12 rare mutations. Prenatal diagnosis is offered if mutations are identified.48
Case: The couple was desirous of prenatal diagnosis and the mutations in both the partners were identified
  • Q.40. How will you carry out prenatal diagnosis in this couple?
Ans: Once the carrier status of the couple is confirmed and the DNA mutations of the couple have been identified, the next step is to offer prenatal diagnosis and selective abortion of fetuses affected with thalassemia. In this couple, prenatal diagnosis can be accomplished by chorionic villi sampling between 11–14 weeks of pregnancy. CVS is preferred as the results of prenatal diagnosis are available early in pregnancy. Usual reporting time is about one week.
  • Q.41. What are the various methods of prenatal diagnosis?
Ans: Prenatal diagnosis of hemoglobinopathies is best accomplished by DNA analysis of cultured amniocytes or chorionic villi by amniocentesis or chorionic villous sampling (CVS).
Early and specific diagnosis by molecular methods has almost completely replaced cordocentesis. Cordocentesis is only performed for the following indications:
  • pregnant patients who report late,
  • CVS is unconclusive,49
  • DNA diagnostic facilities are not available
  • One or both mutations are unidentified or molecular markers for linkage are unin-formative.5014
If the test shows that the baby is affected, the couple is counseled regarding the natural history of the disorder, prospects for treatment and cure and their risk. Termination of pregnancy can be offered upto 20 weeks of gestation.
The role of the genetic counselor and the obstetrician in these cases is extremely important. Even at this stage decision may be taken by the couple to continue the pregnancy accepting the life long treatment of the affected child.
For some couples preimplantation genetic diagnosis in combination with in vitro fertilization may be a desirable option to avoid termination of an affected pregnancy.51
Case: On prenatal diagnosis the fetus is diagnosed to be β thalassemia carrier.
  • Q.42. The couple continues the pregnancy, how will you manage the pregnancy?
Ans: β thalassemia minor is well tolerated pregnancy. Pregnancy outcome and obstetric complications do not differ from general population.
  • Periconceptional folic acid supplementation should be given as the risk of fetal neural tube defects may be increased in pregnant woman who are thalassemia carriers, possibly because of relative folic acid deficiency secondary to increased erythropoiesis. The optimum dosage of folate has not been determined, however, high dose supplementation of at least 4 mg daily should be considered based on benefits in other populations who are at higher risk for neural tube defects.52
  • Iron supplementation should be given and concomitant iron deficiency anemia should be diagnosed (S. Ferritin levels, S iron, total iron binding capacity) and treated.50 In absence of documented iron deficiency anemia, replace ment beyond prophylactic doses of iron is not indicated.51 Parental iron therapy is contra-indicated as it causes iron overload.
  • Fetal growth and well being should be followed. Women with β thalassemia minor are found to have significantly higher rate of intrauterine growth restriction and oligohydramnios than non-thalassemic females.51
  • Q.43. How will you manage pregnant woman with β thalassemia major or thalassemia intermedia?
Ans: Until recently, pregnancy in females with β thalassemia major was extremely rare. However, with the introduction of hypertransfusion and iron chelation therapy several reports have been documented with favorable pregnancy outcome in female with β thalassemia major. Pregnancy should be managed by interdisciplinary team who is familiar with high-risk pregnancy and care of patients with thalassemia.
  • Periconceptional folic acid supplementation should be given.
  • Baseline cardiac, hepatic and endocrine evaluation is recommended at initial visit and should be repeated at second and third trimester.
  • S. ferritin levels and blood counts should be followed regularly.
  • Hemoglobin levels should be maintained at or near 10 gm/dl with transfusions.
  • Fetal growth and well being should be followed closely because of increased risk of intrauterine growth restrictions.
  • Mode of delivery should be individualized with cesarean section reserved for obstetrics indications.
REFERENCES
  1. Cunningham FG, Leveno K, Bloom SL, et al. Prenatal diagnosis and fetal therapy. In Twickler DM, Wendel GD (Eds). Williams Obstetrics 2010;23:287–311.
  1. Fisher B, Rose NC, Carey JC. Principles and Practise of teratology for the obstetrician. Clin Obs and Gynae 2008;51:106–18.
  1. Becerra JE, Khoury MJ, Cordero JF, et al. Diabetes mellitus during pregnancy and the risk for specific Pregnancy with Previous Congenital Disorders 15birth defects: A population- based case control study. Paediatrics 1990;85:1.
  1. Hunter AGW. Neural tube defects in eastern Ontario and western Quebec: Demography and family data. Am J Med Genet 1984;19:45.
  1. Lindhout D, Omtzigt JGC, Cornel MC: spectrum of neural tube defects in 34 infants prenatally exposed to antiepileptic drugs. Neurology 1992;42(suppl 5): 111.
  1. Isotalo PA, Wells GA, Donnelly JG. Neonatal and fetal methylhydrofolate reductase genetic polymorphism: an examination of C677T and A1298C mutations. Am J hum Genet 2000;67:986–90.
  1. Doray B, Favre R, Gasser B, et al. Recurrent neural tube defects associated with partial trisomy 2p22-pter: a report of two siblings and review of the literature. Genet Cous 2003;14:165–72.
  1. Zumel RM, Darnaude MT, Delicado A, et al. Trisomy 20p from maternal translocation and anencephaly. Case report and genetic review. Am Genet 1989;32:247–9.
  1. Godbole K, Deshmukh U, Yajnik C. Nutri-genetic determinants of neural tube defects in India. Indian Pediatrics 2009;46:467–75.
  1. Shaffer LG, Marazita ML, Bodrtha J, Newlin A, Nance WE. Evidence for a major gene in familial anencephaly. Am J Med Genet 1990;36:97–101.
  1. Tanriverdi HA, Hendrik HJ, Ertan K, Schmidt W. Meckel Gruber syndrome: a first trimester diagnosis of a recurrent case. Euro J Ultrasound 2002;5:69–72.
  1. Toriello H V, Higgins J V. Occurrence of neural tube defects among first, second, and third degree relatives of probands: results of a United States study. Am J Med Genet 1983;15:601–06.
  1. Centers of Disease Control and Prevention. Alcohol use among women of childbearing age- United States, 1991–1999. MMWR 51:273,2002a.
  1. Centers of Disease Control and Prevention. Spina bifida and anencephaly before and after folic acid mandate—United States, 1995–1996 and 1999–2000. MMWR53: 362,2004.
  1. Group MRCVSR: Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. MRC Vitamin Study Research group. Lancet 1991;338:131–7.
  1. Blencowe H, Cousens S, Bernadett M, Lawn J. Folic acid to reduce neonatal mortality from neural tube disorders. Int J Epid 2010;39:110–21.
  1. Criezel AE, Dudas I. Prevention of the first occurrence of neural tube defects by periconceptional vitamin supplements. N Engl J Med 1992;327:1832.
  1. Katz VL, Chescheir NC, Cefalo RC: Unnexplained elevation of maternal serum alpha fetoprotein. Obstet Gynaecol Surv 1990;45:719.
  1. Jenkins TM, Wapner RJ. Prenatal diagnosis of congenital disorders. In Creasy RK, Resnik R (Eds): Maternal-Fetal Medicine, Elsevier,  Pennsylvania  2004;5:235–80.
  1. Nicolaides KH, Campbell S, Gabbe D, et al. Screening for spina bifida: Cranial and cerebellar signs. Lancet 12:72,1986.
  1. Sadler TW. Third to eighth weeks: The embryonic period. In Sadler TW (Ed). Langman's medical embryology, Lippincott Williams and Wilkins,  Philadelphia  2006;1:67–88.
  1. Gohsl, Tan JVK, Kwek KYC, Yeo GSH. Recurrent neural tube defects. Singapore Med J 2006;47(8): 728–9.
  1. Peralta CF, Bunduki V, Plese JP, et al. Association between prenatal sonographic findings and postnatal outcomes in 30 cases of isolated spina bifida aperta. Prenat Diag 2003;23:311–14.
  1. Jobe AH: Fetal surgery for myelomeningocele. N Engl J Med 2002;347:230–31.
  1. Walsh DS, Adzick NS, Sutton LN, et al. The rationale for in utero repair of myelomeningocele. Fetal Diagn Ther 2001;16:312.
  1. Cunningham F G, Leveno K, Bloom SL, et al. Genetics. In Twickler DM, Wendel GD (Eds). Williams Obstetrics, McGraw Hill,  United States of America 2010;23:266–86.
  1. Mueller RF, Young ID. Chromosome disorders. In Mueller RF, Young ID (Eds). Emery's elements of medical genetics. Elsevier,  Philadelphia  2002;11:249–66.
  1. Mueller RF, Young ID. Chromosomes and cell division. In Mueller RF, Young ID (Eds). Emery's elements of medical genetics. Elsevier,  Philadelphia  2002;11:29–54.
  1. Boue J, Gallano PA. A collaboration of the segregation of inherited chromosome structural rearrangements in 1356 prenatal diagnosis. Prenat diagn 1984;4:45.
  1. Farndon PA, Kilby MD. Genetics, Risks, and genetic counseling. In James DK, Weiner C P, Steer PJ, Gonik B (Eds): High risk pregnancy, Elsevier,  Pennsylvania  2006;3:43–66.
  1. Rani As, Jyoti A, Reddy PP, Reddy OS: Reproduction in Down's syndrome. Int J Gynaecol Obstet 1990;31:81–86.
  1. Snijders RJM, Sundberg K, Holzgreve W, et al: Maternal age and gestation specific risk for trisomy 21. Ultrasound Obstet Gynecol 1999;13:167.

  1. 16 Cuckle HS, Wald NJ, Thompson SG. Estimating women's risk of having a pregnancy associated with Down's syndrome using her age and serum alpha-fetoprotein level. Br J Obstet Gynaecol 1987;94:387–402.
  1. Daniel A, Hook EB, Wulf G. Risks of unbalanced progeny at amniocentesis to carrier of chromosome rearrangements: Data from United States and Canadian laboratories. Am J Med Genet 1989;33:14.
  1. Saller DN, Canick JA. Current methods of prenatal screening for Down syndrome and other fetal abnormalities. Clin Obs and Gynae 2008;51(1):24–36.
  1. Wald NJ, Rodeck C, Hackshaw AK, et al. First and second trimester antenatal screening for Down's syndrome: the results of the serum, urine and ultrasound screening study (SURUSS). J Med Screen 2003;10:56–104.
  1. Malone FD, Canick JA, Ball RH, et al. First and second trimester evaluation for fetal aneuploidy (FASTER): Principle results of the NICHD multicentric Down syndrome screening study. N Engl J med 2005;353:2001–11.
  1. Said S, Malone FD. The use of nuchal translucency in comtemporary obstetric practice. Clin Obs and Gynae 2008;51(1):37–47.
  1. Souka A, Kaisenbverg CV, Nicolaides KH. Increased nuchal translucency with normal karyotype. In Nicolaides KH(Ed). The 11–13+6 weeks scan, Fetal Medicine Fondation,  London  2004:71–94.
  1. Hyett J, Perdu M, Sherland G, et al. Using fetal nuchal translucency to screen for major congenital heart defects at 10–14 weeks of gestation: population based cohort study. BMJ 1999;318:81–5.
  1. Malone F, Ball R, Nyberg D, et al. First trimester septated cystic hygroma: prevalence, natural history, and pediatric outcome. Obstet Gynaecol 2005;106: 288–94.
  1. Heath V, Nicolaides KH. Sonographic features of chromosomal defects. In Nicolaides KH (Ed): The 11–13+6 weeks scan, Fetal Medicine Fondation,  London  2004: 45–70.
  1. DeVore GR, Romero R. Genetic sonography: An option for women of advanced maternal age with negative triple marker maternal serum screening results. J Ultrasound Med 2003;22:1191–99.
  1. Souter VL, Nyberg DA, Benn PA, et al. Correlation of second trimester sonographic and biochemical markers. J Ultrasound Med 2004;23:505–11.
  1. Sebre N, Nicolaides KH. Multiple pregnancy. In Nicolaides KH(Ed). The 11–13+6 weeks scan, Fetal Medicine Fondation,  London  2004:95–110.
  1. Lee T, Leshane ES, Messerlian GM, et al. Down syndrome and cell free fetal DNA in archived maternal serum. Am J Obstet Gynecol 2002;187:1217–21.
  1. Sanchaisuriya K, Fucharoen S, Fucharoen G, et al. A reliable screening protocol for thalassemia and hemoglobinopathies in pregnancy. Am J Clin Pathol 2005;123:113–18.
  1. Maheshwari M, Arora S, Kabra M, et al. Carrier screening and prenatal diagnosis of β-thalassemia. Indian Pediatrics 1999;36:1119–25.
  1. Panirahi I, Ahmed RPH, Kannan M, et al. Cord blood analysis for prenatal diagnosis of thalassemia major and hemophilia A. Indian Pediatrics 2005;42:577–81.
  1. Hedge UM, Khunda S, Marsh GW, et al. Thalassemia, Iron, and pregnancy. Br Med J 1975;3(5982):509–11.
  1. ACOG practice Bulletin No. 78: Hemoglobinopathies in Pregnancy. Obs and Gynaecol 2007;109(1):229–38.
  1. Rappaport VJ, Velazquez M, Williams K. Hemoglobinopathies in pregnancy. Obstet Gynaecol Clin N Am 2004;31:287–317.