Basics of Vaginal DeliveryUnit 1

This unit is focused on basic maternal and fetai anatomical and physiological facts related to vaginal delivery. Precise and clear concept of these facts and their clinical application is must for obstetrician. Labor room management and record keeping an integral part of obstetrics, is also included in this unit.2

Pelvic girdle is the bony ring through which body weight is transmitted to the lower extremities. In women it is adapted for specialized function of child bearing.

The pelvis is described having four imaginary planes:

It is plane of division between the false and true pelvis. It is bounded posteriorly by sacral promontory, alae of sacrum, laterally by linea terminalis, and anteriorly by horizontal pubic rami and symphysis pubis.4

It has nearly round shape in gynecoid pelvis.

True conjugate that is anteroposterior diameter of pelvic inlet is not the shortest distance between promontory of sacrum and symphysis pubis.

Obstetric conjugate is shortest anteroposterior diameter through which the head must pass in descending through pelvic inlet. Clinically obstetric conjugate cannot be measured by examining fingers.6

So for clinical purpose it is estimated indirectly by first measuring “Diagonal Conjugate” which is determined by first measuring distance from lower margin of symphysis to the promontory of sacrum and then subtracting 1.5 to 2 cm from diagonal conjugate (Fig. 1.1.3).

It is the space between the plane of brim above and the plane of outlet below. It forms a curved canal with shallow anterior wall (3.75 cm) and deep posterior wall (11.25 cm), and 7.5 cm deep lateral wall.7

Plane of widest pelvic dimension: It is bounded in front by center of symphysis pubis and behind by junction of 2nd and 3rd sacral vertebra.

Anatomical outlet: It is a lozenge shaped area, consist of two approximately triangular areas, that are not in the same plane, having common base of imaginary line drawn between two ischial tuberosities (Fig. 1.1.4A).

Obstetrical outlet: It has certain characteristics which play an important role in mechanism of vaginal delivery and obstetric management. These are as follows:

It is an imaginary flat surface bounded in front by lower border of symphysis, laterally by tip of ischial spines and posteriorly by the lower border of the last sacral vertebra (Fig. 1.1.4B).8

The interspinous diameter is 10 cm and somewhat more. It is usually the smallest diameter of pelvis.

Anteroposterior diameter through level of ischial spine normally measures at least 11.5 cm. Its posterior sagittal diameter between the sacrum and line created by interspinous diameter is usually at least 4.5 cm.

Plane of pelvic brim, cavity and outlet are imaginary flat surface bounded by limit of pelvic brim, mid cavity and outlet.

Pelvis has oblique articulation with femur bones, so plane of pelvic brim in erect posture is not an horizontal surface, but is inclined at an acute angle of 55° to the horizontal surface. This is called inclination of pelvic brim.

Because of inclination of pelvic brim the posterior border of brim stands at higher level than the anterior. The sacral 10promontory is 9.4 cm above the upper border of pubic symphysis in erect position (Fig. 1.1.5A).

Axis of pelvic brim is represented by an imaginary straight line drawn perpendicular to the plane of brim at its center. If it is extended upward, it will reach umbilicus and if extended downward, it reaches upto coccyx (Fig. 1.1.5A).11

Obstetric significance: of axis of pelvic brim is that it indicates the direction of fetal descent through pelvis.

Axis of mid plane: It is represented by a line, the direction of which is intermediate between those of pelvic brim and outlet.

Axis of outlet: Axis of pelvic outlet will be represented by a line joining the center of plane of pelvic outlet with sacral promontory. At this plane axis is nearly vertical.

If we unite the axes of planes of brim, mid cavity and outlet, it frames the anatomical axis of pelvis, which travels through the center of canal of bony pelvis (Fig. 1.1.5B).

Fetus passing through the pelvis does not follow the anatomical axis because pelvic cavity is almost cylindrical in upper three fourth parts. So head descends in axis of pelvic inlet till level of ischial spine and then curve forward near the plane of pelvic outlet. This represents obstetrical pelvic axis, through which head passes through pelvis.

Coldwell and Moloy (1933, 1934)^1,2 used special methods of stereo radiography which enabled them to study the architecture of pelvis in life size accurately. The Coldwell Moloy classification of female pelvis is still considered the gold standard for obstetrics and anticipating various obstetrical difficulties and complications in different type of pelvis.12

Clinical assessment of pelvis includes a systematic palpatory assessment of pelvic inlet, cavity and outlet.

Clinical estimation of mid pelvic capacity by any direct form of measurement is not possible. If ischial spines are prominent, concavity of sacrum is shallow then suspicion of a contracted pelvis should be made.

While withdrawing the hand, transverse diameter of obstetrical outlet of the pelvis can be inferred by inserting the finger knuckles of the right hand (or closed fist) between ischial tuberosities. When knuckles of four fingers can be fitted comfortably between two ischial tuberosities, anatomical outlet is considered normal for practical purposes. After a little experience this diameter can be assessed average, small or large. Measurement of more than 8 cm can be considered normal.

Value of observation of clinical pelvimetry is significant only in relation to size of fetal head. So it is a gold standard saying that best pelvimeter is the fetal head.

Descent of biparietal plane of the fetal head to a level below that of pelvic inlet is termed engagement. With engagement, the fetal head serves as an internal pelvimeter to demonstrate that pelvic inlet is ample for that fetus.17

It can be done by:

It is less satisfactory method but in experienced hands gives quite satisfactory information. In engaged head, examining fingers can not reach the lower most part of the head. So if head is pushed downward over lower abdomen, the examining finger will slide over that position of head proximal to the biparietal plane and diverge. On the contrary in unengaged head, examining finger will converge, and easily palpate the lower part of head.

While doing clinical evaluation of pelvis, the situation of lowermost part of fetal head in relation to ischial spine is determined.

When fingers are pressed in position to measure diagonal conjugate, assistant presses upon the fundus of uterus to push the fetal head into pelvis.20

Beside bony pelvis of mother, maternal soft tissue—its anatomy as well variation in thickness, texture, and 21disposition plays an important role in vaginal delivery. Beside this all obstetric operations and maneuvers are done in relation to maternal soft tissues. So it is necessary to have a clear concept of not only the anatomy of pelvic floor and perieneum but also its dynamic changes which occur in process of child birth.

Pelvic floor comprise the soft parts which fill in pelvic outlet. For obstetrical purpose the most important structure of pelvic floor are:

Pelvic facia is visceral layer which springs from the fascia clothing the lateral pelvic wall at level of white line which corresponds to level of ischial spine. This fascia is split into superior and inferior layer to enclose the muscle.

Levator ani muscle slings that originates from the posterior surface of the superior pubic rami, inner surface of ischial spine and obturator fascia.

The urogenital diaphragm is external to pelvic diaphragm.

It is made up of:

The median raphe of levator ani between the anus and vagina is reinforced by the central tendon of the perineum. The bulbocavernous, superficial transverse perineal and external anal sphincter muscle also converge on central tendon. The center of perineal body is 3 cm below the level of a line joining the lower border of symphysis with tip of coccyx.

During vaginal delivery and especially in 2nd stage of labor the vagina that is in center of pelvic floor become enormously dilated and in result the disposition of pelvic floor is changed.23

Understanding the basics of anatomical variation of pelvis and its effect on course of vaginal delivery is foundation of obstetrics. Clinical observation starts right in antenatal period with body mass index estimation, and body shapes variation and continues till delivery of the baby. Correct method of examination of pelvis and clinical diagnosis of fetopelvic proportion or disproportion is one of the basic and important obstetric skill which is to be learnt throughout the obstetric career. Two knowledgeable and sensitive fingers of obstetrician can outweigh the radiological and even MRI examination.

The journey of fetus from maternal passage to outer world is considered most dangerous and difficult one of the human life.

It denotes the relation of long axis of fetus to that of uterine ovoid. It may be longitudinal or transverse or occasionally oblique at 45° angle which is considered unstable and always becomes longitudinal or transverse in course of labor.

Part of fetus which lies below and presents at pelvic brim is called fetal presentation which may be (a) cephalic (b) breech, (c) shoulder.

It is more precisely the particular part of fetal presentation, which first enters the pelvic brim and like wise first to be felt by examining finger during pelvic examinations. In majority of cephalic presentation it is vertex presentation.27

During last weeks of pregnancy the head, trunk and limb of fetus are packed up into smallest possible space in a regular and fairly constant arrangement of generalized flexion—this is termed as fetal attitude.

From obstetrical point of view the characteristic of fetal skull and size of fetal head is important because firstly head is presenting part in more than 90% of labor and secondly an essential feature of labor is the adaptation between the fetal head and maternal bony pelvis.

Where several sutures meet, an irregular space forms, which is enclosed by a membrane and designated as fontanelle. Six fontanelles exist on the fetal skull at term, but only two—anterior and posterior fontanelles are of practical importance.

It is an unequal sided kite shaped piece of unossified membrane, lying in mesial plane between two halves of frontal and two parietal bones. Its angle are continuous with frontal, sagittal and right and left halves of the coronal suture. It measures 3 cm in anteroposterior and 2 cm in transverse diameter. As it lies a little below the general level of the skull, it can felt on the surface as a shallow depression (Fig. 1.2.2—e).

It is a small triangular depressed area at the intersection of the sagittal and lambdoid suture. It is to be noted that it is not an unossified piece of membrane at all but depression, except in a premature fetus (Fig. 1.2.2—c).

These two fontanelles are of great clinical obstetrical significance because they can be recognized during labor via its special characteristics and from them valuable information can be obtained regarding position and attitude of the fetal head.

General shape of the fetal head is that of an ovoid with a long anteroposterior diameter. In a normal attitude of complete flexion, long diameter of fetal head ovoid forms a very acute angle with that of body ovoid (Figs 1.2.3A to D).31

Fetal denominator is a bony point on fetal presenting part in relation to designated location of maternal pelvis. Position refers to the relationship of denominator to right or left side of maternal birth canal. Fetal occiput, chin (mentum) and sacrum are the determining point in vertex, face and breech presentation respectively.

For still more accurate orientation, the relationship of a given position of the presenting part to the anterior, transverse or posterior part of maternal pelvis is considered.

When vertex is engaged in pelvic brim, owing to lateral inclination of head, one parietal bone usually lies at a lower level than other, so the sagittal suture does not correspond precisely to either the transverse or oblique diameter, but lies either in front or behind it.

En route to vaginal delivery through maternal passage, obstetrician is most concerned for the safety of passenger that is fetus, which is going to be delivered.

The positional change in the presenting part required to navigate the pelvic canal constitute the mechanism of labor.

The mechanism by which the biparietal diameter, that is the greatest transverse diameter of fetal head in occiput presentation, passes through the pelvic inlet is designated ‘Engagement’.

Throughout first and second stage of labor there is more or less continuous movement of descent. Descent of fetus is first requisite for birth of newborn. Descent is brought about by following forces:

Flexion is primarily an attitude of fetus but usually at onset of labor head enter the pelvic brim in an attitude of deficient flexion.

This movement consist of turning of the head in such a manner that the occiput gradually moves toward the symphysis pubis anteriorly from its original position or less commonly posteriorly towards the shallow of sacrum. It is essential step for completion of labor unless fetus is unusually small.

The tendency of head for forward or internal rotation of occiput is caused by following anatomic and dynamic factors:

Now head is delivered by movement of extension. When head presses upon pelvic floor, two force acts:43

With progressive distension of perineum and vaginal opening, an increasingly large portion of occiput gradually appears and head is born in following sequence with movement of extension (Figs 1.3.4):

These two movements are movement of neck and trunk and head at this junction is merely the index.

when head emerges in anteroposterior diameter of outlet, the shoulder engage in oblique diameter of brim, so there is slight twist of neck. When head is delivered there is a slight movement, so neck is back into normal relation to the bisacromial diameter.

It is movement of shoulder from oblique diameter of brim to anteroposterior diameter of outlet, and now shoulders are delivered. It can also be called as the internal rotation of the shoulder. This is reflected externally as a passive movement of head which is rotated further in same direction as restitution. So along with restitution, movement of external rotation bring bisacromial diameter into relation with anteroposterior diameter of the pelvic outlet (see Figs 1.3.1G and H).

Immediately after external rotation, the anterior shoulder appears under symphysis pubis and perineum becomes distended by posterior shoulder.

Series of movement of fetus during journey through maternal passage depicts a beautiful harmony created by anatomical and physiological facts and variation of fetal presenting part as well maternal pelvis. Clear understanding of the movement of fetus is one of the basic knowledge which helps obstetrician in conducting vaginal delivery and diagnosing dysfunctional labor.46

“Labor” is the process by which a fetus of viable age is expelled from the uterus. It varies greatly in duration, severity, and risk involved to mother and fetus.

One of most frequently asked question by women is the date of delivery. The date at which labor may be expected cannot be predicted with certainty.47

This physiological process that regulate parturition and onset of labor continue to be defined. Onset of labor represents the culmination of series of biochemical changes 48in uterus that result from endocrine and paracrine signals coming from both the mother and the fetus. Some of the factor that are closely involved are:

Parturition: Bringing forth of young includes all physiological process involved in birthing. It can be divided into four uterine phase (Table 1.4.1), which corresponds to major physiological transition of myometrium and cervix during pregnancy.

Characterized by uterine smooth muscle quiescence with maintenance of structural integrity.

Near end of pregnancy, Myometrium is awakened or activated. This phase represents the sequence of change of uterus during last 6 to 8 weeks of pregnancy.

Women often describe feeling different, restless, odd prior to going into labor. Women experience a shift in their priorities as the birth becomes imminent, evidenced by spurts of energy and nesting activities.

It is synonymous with active labor. That is uterine contraction that brings about progressive cervical dilatation and delivery.

To recognize onset of labor is one of the most difficult part of management of labor. The strict definition of labor— uterine contractions that bring about recognizable effacement and dilatation of cervix—usually does not 51easily help the clinician in determination of time of start of labor because this can only be confirmed retrospectively.

Intermittent contractions recognizable on palpation occur in wall of gravid uterus. But they are usually not perceived by the patient and produce no effect upon the cervix.

It is per vaginal discharge of blood stained mucus which comes from abundantly secreted cervical mucous during labor, and hemorrhage caused by separation of membrane from lower uterine segment at beginning of cervical dilatation.52

The length, dilatation as well texture of cervix before onset of labor, at term is variable. At term the ripe cervix is soft, effaced, slightly patulous and closely applied to head.

On dilatation of cervix, the lower pole of fetal membrane that is chorion and amnion, which has been already separated few weeks before actual onset of labor by stretching of lower uterine segment, now bulge into cervical canal. This bulge of membrane containing a little liquor amni is called the presence of bag of water, which becomes tense and convex during uterine contraction and disappears with passing off the pain.

First stage of labor is stage of dilatation of the cervix which is preparatory to the actual process of birth or expulsion of fetus from the uterus. It's progress or non-progress can be judged clinically by changes taking place in the cervix, external Os and bag of water.

The onset of latent labor as defined by Friedman (1972) is the point at which mother perceives regular contraction and it ends usually between 3 to 5 cm of dilatation.

The concept of a latent phase has helped significantly in understanding normal human labor because labor is considerably longer when a latent phase is included. For women planning hospital birth, home is probably the best place to spend the latent phase and not hospital environment, where fear and anxiety are likely to inhibit labor and attract interventions.⁴

Women may be excited or may be anxious. They usually want confirmation of what is happening to their body as well as seeking reassurance and a rapport with attending person. Primigravidae in their excitement and inexperience of strong labor can sometimes overestimate their progress. They need their excitement and fears acknowledged.⁵

The cervical dilatation of 3 to 5 cm or more, in presence of uterine contraction can be taken to represent threshold for active labor. Cervix of active labor provide useful guidelines and guidepost for labor management. 25% of nulliparaous labor and 15% of multigravid have one or other form of active labor phase abnormalities.⁶

In the earlier stage of labor, the woman may continue to eat and drink or laugh or talk excitably between contraction. As the labor advance the women is less inclined to eat or talk and she will become quieter and behave more instinctively as the primitive part of brain is taken over (Ockenden 2001).¹²58

This stage begins when cervical dilatation is complete and ends with fetal delivery. The presenting part is now passing from the cervix into the vagina and on examination the lip of ext Os can not be felt. In this stage the vagina is gradually dilated from above downwards by the passage through it of the head and body of fetus. In this stage uterus, cervix and vagina is merged into a single broad channel, the boundaries between component parts are obliterated.59

Duration of second stage is 1 to 2 hour in a primigravidae and 10 to 15 minutes in multipara but it may last very much longer than this when the pains are relatively feeble or with malposition.

It is a phase that commonly occurs at the end of first stage of labor. Kitzinger (1987)¹⁵ suggest that it last a few contractions.

The after birth consists of the placenta, umbilical cord, and amnion and chorion membrane. When fetus is expelled, there is sudden and striking reduction in size of uterus.62

The fundus of uterus now lies about level of umbilicus and become alternative hard and soft to touch, signifying that intermittent contractions are continuing but they are painless.

Understanding physical and psychological signs of onset of labor and its different stages are an integral part of management and conduct of vaginal delivery.

Labor room is unique place of hospital, virtually a place of God's creation with its inherent extremes of chaos and confusion, as God is usually in habit of giving its blessings with stern lessons, pain and hard work.

Obstetric patient come to hospital in different stage of labor and some times in critical situations like hemorrhage, fits, malpresentation. Labor room should preferably be located on ground floor of hospital. As it is safe, comfortable for patient and time saving.

Dimension of labor room should be planned keeping in mind, the approximate number of deliveries in hospital and its future possible workload and whether hospital is giving services for high risk obstetrical women or providing delivery facilities for only low risk women. However, it should be kept in mind that at any time low risk women can develop sudden complications.

Equipments and instruments are crucial part of obstetrics. The desired equipment in a well functioning labor room is enlisted in (Tables 1.5.2 and 1.5.3; Fig. 1.5.1).

Nowadays wide variety of berthing beds and tables are available. Very costly labor table are usually not needed but before purchasing one should observe certain feature carefully.

Moreover, labor table should have facilities for quick change of position in all direction, i.e. head high, head low and lateral tilts. Change of position can be done manually, by hydraulic system, electrically or electronically operated system. Hydraulic and electronically operated systems are difficult in maintenance and repair while electrically operated systems are quick, convenient and very easy in maintenance. Labor table should have facility for side support so that patient may not fall in conditions like convulsion, hypovolemia. Lithotomy stirrups should have preferably padded support both on knee and ankle joints. Facility of inbuilt IV drip stand, bucket, support handle for bearing down are optional feature of labor table, which enhances the functioning capacity of table (Figs 1.5.2A and B).70

Good illumination in labor room need special attention as it plays significant role in obstetric management. Main illumination lights should be connected to UPS system which stabilizes voltage and on line electricity supply remains uninterrupted. Beside this invertor facility for few lights should be there. A ceiling shadow less cold light source provides good illumination for two adjacent labor tables. Beside this a shadow less focusing cold light on stand should always be available. It helps a lot in repair of high cervical, vaginal tear or deep episiotomies. There should be provision of adequate number of tube lights. Sun light passing through glazed glass windows also adds to background illumination.

Fully equipped and working anesthetic trolley should be an integral part of major equipments of labor room. Obstetric maneuvers like manual removal of placenta, assisted delivery in malpresentation, etc. require general anesthesia. Beside this high risk women like patients having moderate to severe anemia, severe PIH or postpartum hemorrhage require full cardio respiratory support (Fig. 1.5.3A).

Pulse oxymeter and cardiac monitor add to the safety profile especially in high risk obstetrics. It is a great aid in anticipation as well monitoring of maternal condition in high risk obstetric patient like heart disease, severe anemia, severe PIH, There are equipment available which have combined facility of fetal cardiotocography and maternal pulse oxymetry (Fig. 1.5.3B).72

Neonatal resuscitation station is one of the most important part of labor room and should never be compromised. Pediatric stethoscope, radiant heat warmer, facility of low pressure neonatal suction machine, Amboo bag with mask of different sizes and oxygen supply, pediatric laryngoscope and endotracheal tubes are minimum essential requirement for labor room.

Two good quality stethoscopes, portable fetal Doppler is essential requisite for labor room. However, fetal electrocardiotocography machine aids a lot in decision making in obstetrics and a real cost effective equipment of labor room (Fig. 1.5.3E).

Crash cart is specific trolley having, multiple drawers and place of keeping oxygen gas cylinders. In crash cart emergency life saving drugs, oxytocic drug, suture material, IV fluid, plasma expanders, antihypertensive, diuretic, anticonvulsant drugs should always be kept in specific well leveled drawers for optimum use.

Autoclave and boiler should be separate for labor room for quick sterilization which is often needed in a busy labor room. Even in the hospital where there is central sterilization, labor room should preferably have its own sterilization unit. It makes the staff responsible and self reliant.

Provision of adequate number of cupboards with and without lock should be made in labor room to keep reserve cotton/gauge/for sterilization and cleanup, patient's gown, baby sterilized cloths, (if they are being provided by hospital), stationeries (case sheets, consent forms, blood requisite form, and investigation form), Soaps, washing materials, sterilization material, emergency delivery drug sets, for emergency admissions and extra stethoscope, fetal doppler, extra BP instruments.

Slabs of adequate size made of good quality marble or granite should be made, at comfortable distance from labor table for keeping all cadys with instruments, linen, gauge cotton, etc.

Labor room is a place where twenty four hours in a day and 365 days in a year work is going on. Beside this child birth is a messy and bloody business so it require certain facilities for the patient, attendant and hospital staff, close to labor room. These are as follows:75

A pre-labor ward close to labor room should be an integral part of labor unit. In pre-labor ward the women in latent and first stage of labor are managed under close observation. Patients are shifted to labor room only in late second stage of labor.

If possible there should be an emergency obstetric room close to labor room in which critically ill patient or high risk obstetrical patients can be kept. It helps in isolation, more intensive monitoring and focused management of patients. In this room there should be equipment for maternal resuscitation. Preferably bed should have adjustable facility for lithotomy position. Room should have enough space for minor obstetric procedure, which can be of great help in management of women with ecclampsia, antepartum hemorrhage or post delivery observation in case of any complication.

Labor room should have adjoining scrub room for pre surgical wash up of obstetrician and paramedical staff.76

Habit of good scrub and surgical precaution on the part of labor unit staff helps a lot in long way to reduce many obstetrical short and long-term complications. Scrub room should have facilities of two tap of good qualities with sink of adequate depth and good drainage for simultaneous wash up of two people, geyser, hooks for plastic aprons, gowns and lockers for keeping valuable and belongings.

Adjoining wash area and sinks for fast cleaning of equipments, linen and room, helps a lot in making labor room neat and clean and rapid functioning of paramedical staff.

Doctor/senior staff room should be close to labor room and pre-labor ward. In labor room and pre labor ward close monitoring of mother and fetus is required. Beside this usually the working hours are long and obstetrical work is strenuous. A comfortable place for relaxing and waiting increases the efficiency of staff. It also has positive effect on mood and behavior of staff working in labor room who are usually blamed for rudeness by relatives and women. Staff room should have preferably an attached toilet, sofa cum bed, lockers and cupboard for valuable and belonging, small table with 2–3 chairs. So many times, all of us tend to forget that medical personnel are also human being and in between work, space for a nap, snack or light talk, make work more enjoyable.

Labor room is the most essential and lively place of obstetric working with all its inherent pleasures, dangers and complications of child birth. Availability of a well equipped and well managed labor room is one of the real difference between domiciliary and institutional delivery. Mind and money invested in planning the design of labor room complex, placement of good quality equipments and smooth management of labor room can make the vaginal delivery more safe and satisfying experience for women, relatives as well hospital staff.78

Medicolegal claims in obstetrics are increasing and litigation experts advise that any surgical or obstetrical practice is likely to be judge as being only as good as their written notes.¹

Informed consent to be taken by the person who is of sufficient mental capacity to make the decision and possess all the important, relevant information.³

Note should contain information about:

It should be clear at what time event occurred and what time entry was made.⁵ All time should be entered in the margins using the 24 hours clock. All clinician making entries in the notes should use the same clock.

Case record will be relied upon heavily in a legal investigation. Given the unexpected nature of legal claims, staff that fails to keep clear, contemporaneous records, particularly in the labor ward, may be putting their heads in a noose.82