Pregnancy is a dynamic process, which induces a multitude of anatomic, physiological, biochemical, and psychological changes. Physiological changes during pregnancy allow the body to meet the increased metabolic demands of the mother and fetus by maintaining adequate uteroplacental circulation, and ensure fetal growth and development. These changes begin early in the first trimester and are brought on by the increased circulating levels of progesterone and estrogen, which are produced by the ovary in the first 12 weeks of pregnancy and thereafter by the placenta. While some of these cause a change in biochemical values, others may mimic symptoms of medical disease. For instance, cardiac changes such as sinus tachycardia, systolic heart murmurs, and cardiac enlargement could be interpreted as signs of heart disease. It is thus crucial, to differentiate between normal physiological changes and pathological changes, particularly for clinicians involved in the care of pregnant patient.

A pregnant mother undergoes significant changes in acid-base status as well as sodium and calcium metabolism to combat her physiological needs of pregnancy. Pregnant patients experience mild respiratory alkalosis due to the stimulation of the respiratory center by progesterone. This is associated with a corresponding increase in bicarbonate excretion by kidneys; as a result, the pH remains slightly high (7.40–7.45) but within the normal range. Pregnant women are predisposed to starvation ketosis as compared to nonpregnant states due to relative insulin resistance and increased production of the counter-regulatory hormone. Physiological mild hyponatremia occurs during pregnancy due to increased AVP secretion caused by resetting of osmoreceptors in the hypothalamus at a lower osmolality, but values below 130 mEq/L require a diagnostic workup and intervention. Gestational diabetes insipidus can occur due to increased production or decreased destruction of enzyme vasopressinase. Secretion of parathyroid hormone-related peptide by the placenta and breasts and two- to three-fold increased calcium and phosphate absorption in the maternal gut are the key changes in calcium metabolism during pregnancy. Though rare, both hypo- and hypercalcemia in pregnancy are associated with significant maternofetal morbidity and mortality.

The placenta is a temporary, multifunctional organ composed of both maternal and fetal components. It maintains homeostasis to ensure the growth of the fetus and well-being of the mother. Abnormalities in placental development have been known to be responsible for several disorders of pregnancy. Conditions coincident with pregnancy can upset the homeostasis and result in critical illness, which can greatly impact placental function and in turn affect the fetus. Decreased blood flow, acidemia, hypercarbia, and hypoxia seen in critically ill pregnant mothers can result in fetal death. Understanding the physiological changes and functioning of the maternal–fetal–placental unit will aid in better management of critically ill mothers.

Although no scoring system is as yet fully validated for predicting maternal outcomes in critically ill obstetric patients, prognostication may be done objectively using severity predicting models. General critical care scoring systems which have been studied in obstetric patients are outcome prediction models (Acute Physiology and Chronic Health Evaluation [APACHE] I-IV, Simplified Acute Physiology Score [SAPS] I-III, Mortality Probability Model [MPM] I-IV) and organ dysfunction scores (Multiple Organ Dysfunction Score [MODS], Logistic Organ Dysfunction Score [LODS], Sequential Organ Failure Assessment [SOFA]). General critical care scoring systems may overpredict mortality rates in obstetric patients secondary to an altered physiology of organ systems during pregnancy. Obstetric prediction models were developed keeping in mind the physiological characteristics of obstetric population. They are Modified Early Obstetric Warning System (MEOWS), Obstetric Early Warning Score (OEWS), Maternal Early Warning Trigger (MEWT), and disease-specific obstetric scoring systems. The APACHE II model and MPM II are most often used scoring systems for predicting maternal mortality. The SOFA model is the best predictive model for sepsis in obstetrics. APACHE II and SAPS are more useful for nonobstetric population. Recent studies have also underscored the applicability of the OEWS in intensive care unit (ICU) settings with results comparable to the more elaborate APACHE II and SOFA scores. The Early Warning System helps in identifying acutely deteriorating pregnant and postpartum women in non-ICU settings who may require critical care. Fetal outcomes are largely dependent upon maternal outcomes. Prognostic systems applied to mothers may help in estimation of perinatal mortality and morbidity.

Management of a parturient with an acute abdomen presents unique challenges. We aim to review the common obstetric and nonobstetric causes for acute abdomen in pregnancy, approach to diagnosis, the role of imaging, and management including the scope and timing of operative intervention.

Parturient with heart disease forms a challenging group of patients and requires specialized critical care support in the peripartum period. Maternal heart disease may remain undiagnosed till the second trimester of pregnancy, presenting frequently after 20 weeks of gestation, due to increased demands imposed on the cardiovascular system and pose a serious risk to the life of mother and fetus. Management of critically ill parturient with heart disease must be tailored according to individual assessment of the patient and requires a strategic, multidisciplinary, and protocol-based approach. A dedicated obstetric intensive care unit (ICU) and team effort are the need of the hour.

Acute respiratory distress syndrome (ARDS) is a clinical syndrome characterized by several clinical features and pathological responses involving the respiratory system primarily. Infections (viral), sepsis, and massive transfusion are the commonest causes of ARDS during pregnancy. The majority of them recover with noninvasive ventilatory (NIV) support. NIV is safe in pregnancy provided the center is experienced and has a protocolized patient care pathway. Parturients requiring invasive mechanical ventilation are best managed in experienced centers. PaO₂/FiO₂ targets are higher in parturients compared to nonpregnant patients. Permissive hypercapnia is not a safe option in pregnancy. In severe ARDS with refractory hypoxemia, prone ventilation is a safe option. However, it has to be done in experienced centers. Venovenous ECMO is a safe alternative option in pregnant women with refractory hypoxemia, and delivery has been prolonged to a safe viable age on ECMO. The decision to deliver and the mode of delivery have to be a multidisciplinary decision; primary criterion is maternal survival. Postdelivery, establishing maternal bonding while in ventilatory support facilitates early weaning and minimizes lactation failure.

Almost every endocrine axis is influenced by pregnancy. The diagnosis in acute cases is challenging as the classical symptoms are often masked. Thyroid storm is found in only 1–2% of hyperthyroid parturients (0.1–0.4% of all pregnancies). Burch and Wartofsky scoring system is useful for the identification of thyroid storms. Myxedema coma is an extremely rare complication of overt hypothyroidism with a 20% mortality rate. Diabetic ketoacidosis usually reported in the second and third trimesters carries a risk of fetal loss in 10–25% of cases. The size of the tumor rises in 2.7% of microprolactinomas and 22.9% of macroprolactinomas during pregnancy. Adrenal insufficiency in pregnancy is usually caused by primary adrenal failure, which is mostly autoimmune in origin. Pheochromocytoma may present as preeclampsia during pregnancy. Unrecognized pheochromocytoma is associated with a maternal mortality rate of 50%. Shared decision-making and close coordination between critical care, anesthesiology, obstetrics, and endocrinology can help in assuring good maternal and fetal outcomes.

Hypertensive disorders of pregnancy can be classified as chronic hypertension (present before pregnancy), gestational hypertension (onset after 20 weeks of pregnancy), and preeclampsia (onset after 20 weeks of pregnancy, along with proteinuria and other organ dysfunction). Preeclampsia and related disorders are a major cause of maternal and fetal morbidity and mortality. Preeclampsia is believed to result from an angiogenic imbalance in the placenta circulation. Antenatal screening and early diagnosis may help improve outcomes. Severe preeclampsia is characterized by SBP ≥160 mm Hg, or DBP ≥110 mm Hg, thrombocytopenia (platelet count <100 × 10⁹/L), abnormal liver function, serum creatinine >1.1 mg/dL, or a doubling of the serum creatinine concentration in the absence of other renal diseases, disseminated intravascular coagulation, pulmonary edema, new-onset headache, or visual disturbances. Severe preeclampsia or eclampsia (preeclampsia with seizures) needs ICU management and is the main cause of morbidity and mortality. Severe hypertension can also result in life-threatening intracranial hemorrhage. Blood pressure control, seizure prevention, and appropriate timing of delivery are the cornerstones of the management of preeclampsia. Besides intravenous antihypertensive drugs, intravenous magnesium sulfate is the drug of choice to prevent or treat seizures, when preparing for urgent delivery. At present, delivery remains the most effective treatment for preeclampsia, and organ dysfunction rapidly recovers after delivery. Novel therapeutic interventions are under development to reduce complications.

Sepsis is a leading cause of maternal morbidity with a high case fatality rate and leads to significant perinatal loss. Early identification and appropriate time management can significantly improve maternal and perinatal outcomes. The physiological changes of pregnancy and puerperium make pregnant women more susceptible to sepsis and also pose a challenge for early diagnosis because of overlap of clinical features and laboratory values. The validation of scoring/warning systems for sepsis in parturient needs further research. Infections during puerperium are commonly polymicrobial in nature and warrant broad-spectrum antibiotics. Maternal resuscitation in antepartum period has to be tailored to ensure fetal well-being and adequate placental perfusion. For the management of sepsis in pregnancy, the guidelines from surviving sepsis campaign (SSC) for general adult population are extrapolated with modifications related to physiological alterations in pregnancy and puerperium. Timing of delivery is based on the obstetric indications unless the source of sepsis is intrauterine.

Postpartum hemorrhage (PPH) is one of the common causes of morbidity as well as mortality among pregnant women. Obstetric hemorrhage embolization (OHE)/uterine artery embolization (UAE) is the preferred treatment for PPH which has failed medical therapy. In cases of placental accreta spectrum (PAS), balloon catheter can be prophylactically placed in internal iliac arteries (IIAs) bilaterally before delivery to enable postpartum control of bleeding. An inferior vena cava (IVC) filter can be placed under fluoroscopy for a pregnant woman with deep vein thrombosis (DVT) for whom anticoagulation is contraindicated or needs to be stopped at the time of labor. Injection of chemical into the gestational sac can be performed under ultrasonography (USG) guidance to treat ectopic pregnancy. Percutaneous or transvaginal drainage of a collection can be done by ultrasound or computed tomography (CT) guidance for puerperal sepsis. Percutaneous nephrostomy (PCN) is performed for obstructive ureterolithiasis in case of urosepsis or significant stone burden. Sonography should be used for the guidance of interventional radiology (IR) procedures whenever possible. Fluoroscopy must be used only if necessary, giving special attention to radiation-sparing maneuvers.

The critically ill obstetric patient presents unique challenges. However, the general code of conduct, legal processes, and ethical principles continue to apply. Professionals need to keep themselves informed about the requirements of provisions within the legal framework.

Diagnostic tests are used to differentiate between those with and without disease. In this article, we examine some of the properties of diagnostic tests, such as sensitivity, specificity, predictive values, and receiver operating characteristic curves.