#410 ‒ The biology of pregnancy: physiologic adaptation, gestational diabetes, preeclampsia, childbirth, and long-term maternal health | Kathryn Gray, M.D., Ph.D.

What It Covers

Peter Attia interviews Dr. Kathryn Gray, Division Chief of Maternal Fetal Medicine at the University of Washington, covering the full physiologic arc of pregnancy — from plasma volume expansion and hormonal shifts in the first trimester through gestational diabetes, preeclampsia, delivery decisions, and how pregnancy complications predict a woman's long-term cardiovascular and metabolic disease risk decades later.

Key Questions Answered

• •Pregnancy as metabolic stress test: Plasma volume expands 50% by 20 weeks, creating relative anemia and dramatically increased cardiac demand. Women with pre-existing heart or lung disease may be unable to tolerate this expansion, making pregnancy life-threatening. Simultaneously, insulin resistance increases in the second trimester as an adaptive mechanism to preferentially fuel fetal growth — but this same mechanism causes gestational diabetes in a clinically significant subset of women.
• •Gestational diabetes screening window: Screening occurs between 24–28 weeks using a non-fasting 50g one-hour glucose challenge, with a threshold of 130–140 mg/dL. Failing triggers a fasting 3-hour, 75g confirmatory test. First-line treatment is dietary modification with glucose monitoring targets of fasting under 95 mg/dL and one-hour postprandial under 140 mg/dL. When more than half of values exceed targets within days, insulin — not metformin — is the preferred medication due to superior efficacy and neonatal outcome data.
• •Gestational diabetes predicts type 2 diabetes: Fifty percent of women diagnosed with gestational diabetes will develop type 2 diabetes later in life. Standard of care includes a two-hour glucose tolerance test at the six-week postpartum visit and ongoing surveillance thereafter. Lifestyle counseling on diet, exercise, and weight management is especially critical for this population, as these interventions directly reduce conversion risk — yet follow-up rates among young mothers remain low due to competing demands.
• •Preeclampsia mechanism and long-term risk: Preeclampsia — affecting 5–7% of pregnancies — stems from inadequate placental trophoblast invasion of maternal spiral arteries, causing placental hypoxia. The placenta releases sFLT1, which sequesters VEGF and disrupts endothelial function in both maternal vessels and kidney glomeruli, explaining simultaneous hypertension and proteinuria. Women who experience preeclampsia carry elevated lifetime risk of hypertension, cardiovascular disease, and kidney disease — risks driven partly by shared genetic architecture with essential hypertension.
• •Obstetric history as cardiovascular screening tool: Pregnancy functions as a high-intensity physiologic stress test that unmasks genetic predispositions to hypertension and metabolic disease. Genome-wide association studies show that top genetic hits for preeclampsia overlap significantly with those for essential hypertension. Primary care physicians should routinely ask about preeclampsia and gestational diabetes history during any adult health assessment, as these events predict future cardiometabolic risk and should trigger earlier, more aggressive preventive monitoring and intervention.
• •C-section rates and placenta accreta risk: U.S. cesarean delivery rates have risen from roughly 10% to approximately 30% of all births. Each prior cesarean increases risk of placenta accreta spectrum in subsequent pregnancies — where the placenta abnormally invades the uterine wall and fails to detach at delivery. Low transverse uterine incisions carry under 1% uterine rupture risk in future labors, while classical vertical incisions carry roughly 10% rupture risk, making future vaginal delivery contraindicated for that group.
• •Folate timing and neural tube defects: Folic acid deficiency increases neural tube defect risk, but by the time most women confirm pregnancy, the neural tube has already formed — making pre-conception supplementation essential. Women eating well-balanced diets with fruits, vegetables, and fortified whole grains may have adequate levels without supplements. Neural tube defects range from survivable myelomeningocele — where in-utero surgical repair can improve long-term ambulatory and bladder function — to lethal anencephaly, which still occurs in current clinical practice.