Chapter 10: Anatomy & Physiology of Pregnancy

Anatomy & Physiology of Pregnancy begins by establishing a standardized language for obstetrical history, utilizing the GTPAL system—representing gravidity, term births, preterm births, abortions, and living children—to provide a clear clinical picture of a patient's reproductive background. Diagnostic accuracy is highlighted through the discussion of human chorionic gonadotropin (hCG), the primary biomarker detected in modern ELISA-based pregnancy tests, which can identify pregnancy shortly after implantation. Clinical indicators of pregnancy are categorized into three levels: presumptive signs like nausea and fatigue, probable signs such as cervical softening (Goodell sign) or bluish vaginal discoloration (Chadwick sign), and positive signs that definitively confirm a fetus, including audible fetal heart tones or ultrasound visualization. The reproductive system undergoes massive changes, with the uterus expanding through hypertrophy and hyperplasia to accommodate the growing fetus, while the breasts prepare for lactation by producing colostrum by the end of the first trimester. The cardiovascular system experiences a significant 40 to 50 percent increase in total blood volume, leading to physiological anemia because plasma volume expands more rapidly than red blood cell production. This system also adapts by increasing cardiac output and heart rate, though patients must be wary of supine hypotension syndrome, which occurs when the heavy uterus compresses the vena cava while lying on the back. Respiratory adaptations include increased oxygen consumption and a shift to thoracic breathing as the diaphragm is displaced upward, often resulting in a state of mild respiratory alkalosis. The renal system sees a rise in the glomerular filtration rate, which can lead to the excretion of glucose and protein, while the slowing of urine flow increases the risk for infections. Skin changes are often visible as hyperpigmentation, including the "mask of pregnancy" (chloasma) and the linea nigra, alongside the development of stretch marks known as striae gravidarum. Musculoskeletal shifts, such as the exaggerated lumbar curve called lordosis, help maintain balance as the center of gravity moves forward, though this often causes back discomfort and joint laxity. Digestion is affected by high progesterone levels that relax smooth muscles, leading to common issues like heartburn, constipation, and morning sickness. Finally, the endocrine system orchestrates this entire process through hormones like progesterone, which maintains the pregnancy by relaxing the uterus, and estrogen, which promotes tissue growth and increased vascularity.