Pregnancy Physiology Overview - Anatomy and Physiology
- What causes the physiologic (dilutional) anemia of pregnancy?
- Plasma volume rises more than red cell mass, so hematocrit and hemoglobin concentration fall even though total red cells increase.
- What is the main function of human chorionic gonadotropin (hCG) in early pregnancy?
- It maintains the corpus luteum so it keeps secreting progesterone and estrogen until the placenta takes over.
- How does maternal cardiac output change during pregnancy?
- It increases by about 30 to 50 percent, due to both a higher stroke volume and a higher heart rate.
- What does the hormone relaxin do during pregnancy?
- It loosens pelvic ligaments, including the pubic symphysis, and helps soften the cervix in preparation for delivery.
- By about when does the placenta take over most progesterone production from the corpus luteum?
- Around the end of the first trimester (roughly 8 to 12 weeks), after which the corpus luteum is no longer required.
- By roughly how much does maternal blood volume increase by late pregnancy?
- By about 40 to 50 percent, mostly from an increase in plasma volume.
- Why is maternal arterial PCO2 lower than normal during pregnancy?
- Progesterone stimulates ventilation, mainly by raising tidal volume, producing a mild compensated respiratory alkalosis.
- Which hormone causes milk ejection (let-down) during breastfeeding?
- Oxytocin. It contracts myoepithelial cells around the alveoli, while prolactin drives milk production.
- How does human placental lactogen (hPL) affect maternal metabolism?
- It increases maternal insulin resistance and lipolysis, sparing glucose for the fetus.
- Which hormone stimulates uterine contractions in labor through a positive feedback loop?
- Oxytocin. Cervical stretch triggers more oxytocin release, which strengthens contractions until delivery.
- A woman at 34 weeks of pregnancy feels faint when lying flat on her back. What is the most likely cause?
- The uterus compresses the inferior vena cava, reducing venous return and cardiac output (supine hypotension). Lying on the left side relieves it.
- What are two key roles of progesterone during pregnancy?
- It maintains the endometrium (decidua) and keeps the myometrium relaxed, suppressing uterine contractions.