OB | Maternal Adaptations

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1. Pregnancy Confirmation Signs Pregnancy is diagnosed through three categories of signs. Presumptive signs are subjective changes the patient experiences, like amenorrhea, nausea, and breast tenderness. Probable signs are objective findings by a provider, including a positive pregnancy test, Hegar’s sign (softening of the lower uterus), Goodell’s sign (cervical softening), and Chadwick’s sign (bluish-purple cervical discoloration). Positive signs offer 100% accuracy and include ultrasound verification, auscultating fetal heart tones, and provider-palpated fetal movement.

2. Critical Systemic Adaptations

• Cardiovascular: Blood volume surges by 30% to 50% to perfuse the enlarging uterus. Because plasma volume expands faster than red blood cell production, patients experience physiologic anemia of pregnancy. Pregnancy also induces a hypercoagulable state via increased fibrinogen to prevent hemorrhage, raising the risk of thrombosis. Supine hypotensive syndrome occurs when the gravid uterus compresses the inferior vena cava while lying flat, severely reducing cardiac output; this is reversed by resting in a left-lateral position.
• Gastrointestinal: Elevated progesterone causes widespread smooth muscle relaxation, leading to delayed gastric emptying, severe heartburn, and decreased peristalsis which results in constipation.
• Renal/Urinary: The kidneys must filter maternal and fetal waste, causing the glomerular filtration rate (GFR) to increase by up to 50%, which often requires therapeutic medication dosage adjustments.
• Respiratory: Oxygen consumption increases, and tidal volume expands by 30% to 40%. The growing uterus pushes the diaphragm upward, converting breathing from abdominal to thoracic.

3. Placental Endocrine Functions The placenta acts as a crucial endocrine organ:

• hCG: Maintains the maternal corpus luteum until the placenta takes over hormone synthesis.
• Progesterone: Known as the "hormone of pregnancy," it maintains the endometrium, prevents premature uterine contractions, and causes systemic smooth muscle relaxation.
• hPL (Human Placental Lactogen): Acts as a maternal insulin antagonist. It decreases maternal tissue sensitivity to insulin, ensuring a steady, constant supply of glucose crosses the placenta for the growing fetus.

4. Nutritional Requirements & Risks

• Weight Gain: Recommendations strictly depend on prepregnancy BMI. Patients with a Normal BMI (18.5–24.9) should gain 25 to 35 lbs. Underweight patients need 28–40 lbs, while obese patients should gain 11–20 lbs.
• Supplementation: Diets must be supplemented with iron for blood volume expansion and folic acid (400–800 mcg/day) to prevent fetal neural tube defects.
• Hazards: Patients must avoid high-mercury fish (swordfish, king mackerel) to protect fetal neurodevelopment. To prevent Listeriosis—which can cause miscarriage or neonatal sepsis—patients must strictly avoid unpasteurized dairy, raw sprouts, soft cheeses, and unheated deli meats.
• Pica: The compulsive consumption of nonfood items (e.g., dirt, ice, laundry starch) is closely associated with severe iron-deficiency anemia and poor weight gain.