410 ‒ The biology of pregnancy: physiologic adaptation, childbirth, and long-term maternal health

Episode Overview

• In this episode, host Peter Attia, M.D., speaks with Katie Gray, M.D., Ph.D.—a physician-scientist, Maternal-Fetal Medicine specialist (high-risk obstetrician) at a university hospital referral center in Seattle, and immunology Ph.D.—about how pregnancy acts as a profound physiological stress test on the female body.
• The conversation follows a chronological arc through gestation, beginning with early endocrine transitions, plasma volume expansion, and first-trimester fetal organogenesis, before moving into second- and third-trimester complications like gestational diabetes, preeclampsia, and HELLP syndrome.
• They explore the mechanics and risks of labor and delivery, covering vaginal births, C-section scar variations, breech presentations, preterm premature rupture of membranes (PPROM), and the surprisingly high incidence of stillbirth in the United States.
• Throughout the discussion, Gray highlights critical gaps in obstetric science—noting that pregnancy research is historically underfunded by the NIH/NICHD—and emphasizes how pregnancy complications unmask a woman's lifelong genetic predispositions to cardiovascular, metabolic, and renal diseases.

Key Concepts

• Immunology and Mitochondrial Apoptosis: During her Ph.D. research, Gray studied a novel benzodiazepine identified via a drug screen that helped treat autoimmune lupus in mice. By isolating mitochondria from cow hearts, she showed that the compound acted on the mitochondrial ATPase to induce cellular apoptosis. Because the original drug had poor solubility, a derivative that acts locally in the gut is now in clinical trials for inflammatory bowel disease (IBD).
• Pregnancy as a Cardiometabolic Stress Test: Pregnancy forces two massive physiological adaptations: a 50% expansion in maternal plasma volume (peaking by 28 weeks and causing a relative anemia) and a shift from insulin sensitivity to insulin resistance in the second half of pregnancy driven by placental growth. Women with severe cardiopulmonary disease cannot tolerate this 50% volume increase and are advised against pregnancy (or may require a life-saving abortion, as administering diuretics would effectively terminate the pregnancy). Furthermore, failing these physiological stress tests via preeclampsia or gestational diabetes unmasks future risk for chronic hypertension, cardiovascular disease, chronic kidney disease, and type 2 diabetes.
• First-Trimester Endocrinology and Organogenesis: Initially, the ovary supports pregnancy by producing estradiol and progesterone until 8 to 10 weeks gestation, when the developing placenta takes over hormone secretion (which is why IVF patients require hormone supplementation for the first several weeks). All fetal organ formation occurs in the first trimester and is essentially complete by the end of it, when the fetus is roughly 1.5 to 2 inches long. Average maternal weight gain in this first trimester ranges widely from 0 to 10 pounds.
• Hyperemesis Gravidarum and GDF15: While human chorionic gonadotropin (hCG) was long assumed to drive morning sickness, genetic studies of women with extreme nausea and vomiting (hyperemesis gravidarum) flagged the GDF15 gene as a primary driver, making it a new therapeutic target. Severe hyperemesis requiring hospitalization for IV hydration or nutrition occurs in less than 1% of pregnant patients, tends to recur in all subsequent pregnancies, and primarily threatens maternal hydration and nutrition rather than the early fetus, which takes what it needs from the mother.
• Folate and Neural Tube Defects (NTDs): Folic acid deficiency increases the risk of NTDs, which occur before most women realize they are pregnant (especially given that 50% of pregnancies are unplanned). At Gray's Seattle referral center, they see a case of NTDs every month and saw two cases of anencephaly (complete failure of the brain and cranium to form) that year. The most common NTD is myelomeningocele (exposed spinal cord at the base of the spine), which in eligible cases can be repaired via in utero fetal surgery to improve lower-extremity ambulation, bowel/bladder function, and reduce brain fluid accumulation that otherwise requires lifelong shunting. Why folate deficiency causes mild lower-spine defects in one fetus and anencephaly in another remains unknown.
• Gestational Diabetes Pathophysiology and Risk: Because risk-factor screening alone missed 50% of cases, universal screening between 24 and 28 weeks is standard (diagnosing earlier does not improve outcomes). Uncontrolled maternal hyperglycemia exposes the fetus to high glucose, causing the fetus to ramp up its own insulin production. This leads to fetal macrosomia (excessive growth), increased risk of C-section and shoulder dystocia, increased preeclampsia risk, long-term offspring metabolic risk, and neonatal hypoglycemia right after birth once the hyperinsulinemic baby is detached from the placenta. While true gestational diabetes resolves immediately upon delivery, 50% of affected mothers will develop overt type 2 diabetes later in life.
• Preeclampsia and HELLP Syndrome: Affecting 5% to 7% of U.S. pregnancies (most commonly in first pregnancies and women at the extremes of age, such as very young or over 40), preeclampsia is new-onset hypertension (140 mmHg systolic or 105–110 mmHg diastolic) after 20 weeks gestation, accompanied by proteinuria or severe features (headaches, vision changes, right upper quadrant pain, low platelets, elevated liver enzymes, or elevated creatinine). As discovered by Gray's former mentor Ananth Karumanchi at Beth Israel, failed invasion of maternal spiral arteries by placental trophoblasts leaves vessels narrow and high-pressure, causing placental hypoxia. The hypoxic placenta releases massive amounts of the anti-angiogenic protein sFlt into maternal blood, which binds and soaks up VEGF (vascular endothelial growth factor), damaging maternal blood vessel endothelium (causing hypertension) and kidney glomerular endothelium (causing proteinuria). Left untreated, it progresses to eclampsia (seizures), stroke, organ failure, and death. Maternal genome-wide association studies (GWAS) over the last ~8 years show top genetic hits for preeclampsia overlap with top hits for essential hypertension. Whether preeclampsia directly damages vessels long-term or simply unmasks genetic risk is an active, unsettled area of research. A severe variant, HELLP syndrome (Hemolysis, Elevated Liver enzymes, Low Platelets), has an unknown etiology and cannot be managed expectantly. While proteinuria and baseline normal kidney function generally recover after delivery, preeclampsia hypertension often requires medication for 6 to 12 weeks postpartum, and many women develop chronic hypertension within 5 to 10 years.
• Cesarean Section Mechanics and Uterine Rupture: U.S. C-section rates have risen from ~10% historically to ~30% in academic centers today, with about 20% of anticipated vaginal deliveries converting to C-sections. Multiple prior C-sections increase the risk of placenta accreta spectrum, where the placenta invades abnormally into the uterine wall and fails to detach. The type of uterine incision dictates future labor safety: a low transverse incision (horizontal cut in the less muscular lower segment) carries a 1% or less risk of uterine rupture during subsequent labor, whereas a classical incision (vertical cut through the upper muscular uterus, often used in very preterm deliveries) or extensive fibroid removal carries a ~10% rupture risk, contraindicating future labor. Regarding microbiome transfer ("vaginal seeding") after C-sections, Gray notes there is no epidemiological data linking C-sections to gut disorders to her knowledge, and advises parents not to stress over it.
• Breech Presentation, Nuchal Cords, and Labor Mechanics: Medicine still does not know what triggers the onset of human labor or why most breech babies fail to turn head-down. Because a singleton breech baby's head is the largest part and delivers last—risking fatal head entrapment—ACOG recommends a scheduled C-section if the baby remains breech. Conversely, a nuchal cord (umbilical cord wrapped around the neck) occurs in one-third (33%) of all deliveries and rarely causes problems beyond variable decelerations on heart tracings. During labor, cervical dilation alone does not define active labor (some women sit at 3 to 4 cm for weeks, while others at 4 cm contract painfully every 3 minutes). Most labor pain stems from hours of uterine contractions, while delivering the head takes roughly 30 seconds; "back labor" typically occurs when the fetus is occiput posterior ("sunny-side up") rather than occiput anterior.
• Stillbirth Epidemiology and Evaluation: Defined as fetal demise after 20 weeks gestation, stillbirth occurs in 1 in 160 U.S. pregnancies. Even when evaluated with the three most useful diagnostic tools—placental pathology, fetal autopsy, and genetic testing—approximately 50% of stillbirths remain completely unexplained. Umbilical cord Doppler ultrasound is only beneficial in growth-restricted fetuses (or specific indications), not for general stillbirth screening.
• Prenatal Genetic Screening Evolution: Invasive diagnostic testing (amniocentesis and chorionic villus sampling [CVS]) has declined due to cell-free DNA screening, which analyzes placental DNA fragments via a maternal blood draw as early as 9 or 10 weeks. While older maternal serum protein screens (measuring 3 or 4 proteins) had a positive predictive value of only 5% for Down syndrome (a 95% false-positive rate), cell-free DNA has vastly superior sensitivity and specificity. However, it is not a comprehensive genetic screen; it primarily detects Trisomies 21, 18, and 13, and fetal sex.
• Postpartum Physiology and Healthcare Policy: In the first two weeks after birth, massive drops in estrogen and progesterone Alongside HPA axis shifts commonly cause "postpartum blues"; symptoms persisting beyond that window indicate postpartum depression. While lactation suppresses estrogen, progesterone, and ovulation, missing even a single feeding breaks this suppression. On a policy level, pregnancy-related Medicaid coverage in some states historically ended at 60 days postpartum—right in the critical window when many maternal deaths occur—making Medicaid extension a major lever for reducing maternal mortality.

Quotes

• At 0:03:30 - "Why do people go into labor? Why do people have preterm labor? Why do people have preeclampsia? The answer is we don't, we don't know." - Gray highlighting the fundamental biological mysteries that persist in obstetrics due to complexity and historical underfunding.
• At 0:05:51 - "It's a cardiovascular stress test because the plasma volume expands so much. It is a metabolic stress test because there's increased insulin resistance, especially in the second part of pregnancy, that causes some people to have gestational diabetes, and it often can unmask like future predisposition to disease through this process." - Gray establishing the central framework of pregnancy as a window into a woman's future cardiometabolic health.
• At 0:07:35 - "As the placenta develops, the placenta itself starts to secrete the hormones that, you know, support the pregnancy." - Explaining the 8-to-10-week endocrine transition from ovarian to placental hormone production.
• At 0:09:20 - "When they studied folks who had hyperemesis, they found a signal that flagged the GDF15 gene as really important in driving who develops that condition, and so that's actually now a developing target for therapeutics in that area." - Discussing recent genetic discoveries that overturned older assumptions about morning sickness.
• At 0:12:04 - "It starts immediately and kind of peaks at being total, it increased by 50% by 28 weeks." - Describing the timeline and magnitude of maternal plasma volume expansion.
• At 0:13:41 - "Well, it's, it's complex, right? 50% of pregnancies aren't planned." - Explaining the real-world difficulty of optimizing preconception health and counseling women with severe cardiopulmonary conditions.
• At 0:17:32 - "There's good evidence that folic acid deficiency increases the risk of having a neural tube defect in the baby, and by the time you recognize the pregnancy, it's already kind of too late to bring up folic acid levels if they have been deficient." - Emphasizing why folate supplementation must begin before conception.
• At 0:22:27 - "Well, another really important thing that's happening entirely in the first trimester is formation of all the organs of the, of the fetus. So by the time the first trimester is done, that's basically complete." - Clarifying why the first trimester is the critical window for structural organogenesis.
• At 0:26:04 - "Because the reason it became the norm is that by risk factors, we missed half the people who developed gestational diabetes." - Explaining why universal glucose screening between 24 and 28 weeks replaced targeted risk-factor screening.
• At 0:32:49 - "Insulin is really first line, so that's different than outside of pregnancy." - Noting that insulin is preferred over oral agents like metformin for gestational diabetes due to superior safety and neonatal outcome data.
• At 0:36:25 - "So preeclampsia is a pregnancy-specific condition where folks develop new-onset high blood pressure or hypertension after 20 weeks gestation, and often accompanied by proteinuria, so protein in the urine." - Providing the clinical definition of preeclampsia.
• At 0:41:52 - "And the placenta itself then releases this anti-angiogenic factor called sFlt into the maternal circulation, and that molecule soaks up the VEGF, an important growth factor for maintaining vessel endothelial cell function, and that affects both the endothelial cells of the maternal vessels and the endothelial cells in the glomerulus of the kidney." - Detailing Ananth Karumanchi's discovery of how a hypoxic placenta causes systemic maternal vascular and renal injury.
• At 0:45:31 - "But ultimately, it won't go away until the baby is delivered. There's nothing that we can do besides that to actually cure it." - Explaining that while preeclampsia can be managed expectantly with antihypertensives, delivery of the placenta is the only definitive cure.
• At 0:50:06 - "HELLP syndrome is one of those conditions where we often give betamethasone to help mature the baby's lungs, and we wait 48 hours and then we deliver, because we don't expectantly manage somebody who has HELLP syndrome." - Contrasting the urgent delivery protocol for HELLP syndrome with the expectant management of standard preeclampsia.
• At 0:56:58 - "In the very first maternal GWAS of preeclampsia, genome-wide association study, the top hits that were genome-wide significant were some of the top hits in genome-wide association studies of hypertension." - Linking the genetic architecture of preeclampsia directly to essential hypertension.
• At 0:58:10 - "So 50% of patients who have gestational diabetes will develop type 2 diabetes." - Quantifying the massive long-term metabolic risk unmasked by gestational diabetes.
• At 1:11:08 - "A third of the time the baby comes out with a cord around the neck. It's very common. It usually doesn't cause a problem." - Reassuring listeners that nuchal cords are a frequent, typically benign occurrence during birth.
• At 1:26:28 - "Well, I'm not saying that there's no helpful component of that, but I would say of all the things that help determine your health and your baby's health, that's probably not the thing to stress about." - Addressing popular anxiety around C-sections, vaginal seeding, and the infant gut microbiome.
• At 1:29:08 - "Correct, but you only have to miss one feeding to make it not be a good form of birth control." - Warning against relying on lactation-induced ovulation suppression for contraception.
• At 1:47:07 - "Of anticipated vaginal deliveries, about 20% end up going to C-section." - Setting realistic expectations for labor outcomes among women planning a vaginal birth.

Takeaways

• Supplement Folic Acid Before Conception: Because the fetal neural tube forms before most women know they are pregnant—and 50% of pregnancies are unplanned—women of reproductive age should maintain adequate folate through a balanced diet (fruits, vegetables, whole grains, fortified foods) and start prenatal vitamins containing folic acid prior to trying to conceive.
• Manage Severe Morning Sickness Early: If experiencing severe nausea and vomiting in pregnancy, use safe, standard antiemetics like Zofran and prioritize maternal hydration and nutrition, seeking IV fluids if unable to keep liquids down.
• Complete Two-Step Gestational Diabetes Screening at 24–28 Weeks: Undergo the universal 1-hour non-fasting 50g glucose challenge test between 24 and 28 weeks. If your blood glucose exceeds the 130 or 140 mg/dL cutoff (values over 200 mg/dL are automatically diagnostic), complete the fasting 3-hour 75g oral glucose tolerance test (diagnosed if fasting glucose is elevated, or if two of the 1-, 2-, or 3-hour marks are elevated).
• Control Gestational Diabetes with Diet and Insulin: If diagnosed with gestational diabetes, work with a nutritionist and monitor blood sugar to keep fasting levels under 95 mg/dL and 1-hour postprandial levels under 140 mg/dL. If more than half of your readings exceed targets over 1 to 2 weeks, initiate insulin (first-line over metformin). Follow up with a 2-hour oral glucose test at your 6-week postpartum visit to screen for overt type 2 diabetes.
• Treat Pregnancy Hypertension with Pregnancy-Safe Agents: Attend all third-trimester prenatal visits to catch preeclampsia early. If antihypertensive therapy is required during pregnancy or while managing preeclampsia, use first-line agents with proven fetal safety data like nifedipine or labetalol, and strictly avoid ACE inhibitors and ARBs until postpartum.
• Consider External Cephalic Version for Breech Babies at 37 Weeks: If a singleton fetus is still breech at ~37 weeks, discuss attempting an external cephalic version (manually turning the baby from the outside of the abdomen, optionally with anesthesia), which carries a 50% success rate and can help avoid a mandatory breech C-section.
• Base VBAC Decisions on Your Exact Prior Uterine Scar: Before attempting a trial of labor after a C-section, verify the direction of the previous uterine incision (not the skin scar). A prior low transverse incision is generally safe to labor (<1% rupture risk), whereas a prior classical vertical incision or extensive fibroid removal carries a ~10% rupture risk and requires a scheduled C-section.
• Follow the "5-1-1" Rule and Warning Signs in the Third Trimester: Go to the hospital immediately in the third trimester if you experience decreased fetal movement, vaginal bleeding, leaking amniotic fluid, or painful contractions occurring closer than 5 minutes apart for more than 1 hour. If your water breaks at term without contractions, expect induction with Pitocin (oxytocin) to achieve delivery within ~24 hours and minimize infection risk; if PPROM occurs preterm (e.g., at 28 weeks), expect inpatient hospitalization up to 34 weeks and a short course of antibiotics at presentation to prolong latency.
• Maintain Accustomed Exercise and Side-Sleeping: Avoid bedrest during a healthy pregnancy. Continue exercises your body is already accustomed to—including running and resistance training—provided you do not have a short cervix or threatened preterm labor, but do not start a brand-new intensive regimen (like marathon training) and avoid activities with high fall or abdominal trauma risk (downhill skiing, horseback riding) in the second half of pregnancy. In late pregnancy, favor sleeping tilted or on your side rather than flat on your back to avoid vena cava compression.
• Use Non-Hormonal or Dedicated Contraception While Breastfeeding: Do not rely on breastfeeding as birth control; because missing even a single feeding terminates the hormonal suppression of ovulation, implement a reliable contraceptive method postpartum.
• Utilize Cell-Free DNA Screening Starting at 9–10 Weeks: Take advantage of non-invasive prenatal testing (cell-free DNA via maternal blood draw) starting at 9 to 10 weeks for highly accurate screening of Trisomies 21, 18, and 13, while understanding it does not screen for all genetic conditions.
• Use Obstetric History to Drive Lifelong Preventive Cardiology and Primary Care: If you experience gestational diabetes, preeclampsia, or HELLP syndrome, report this history to your primary care physician as a major risk factor. Use it to initiate early, aggressive screening and preventive strategies for type 2 diabetes, chronic hypertension, chronic kidney disease, and cardiovascular disease, and ensure depression screening at the 6-week postpartum visit.