Physiological Changes During Pregnancy

Key Physiological Changes

• Hematocrit decreases during pregnancy due to disproportionate plasma volume expansion compared to red blood cell mass, resulting in physiologic anemia of pregnancy 1
• Pregnancy causes hyperventilation with hypocapnia (decreased CO2), not hypercapnia, with progesterone stimulating the respiratory center, leading to increased minute ventilation and a compensated respiratory alkalosis 1
• Early pregnancy (first trimester) is characterized by an anabolic state with enhanced insulin sensitivity and increased conversion of glucose to glycogen for storage 1
• Gonadotropin levels (particularly hCG) are markedly elevated during pregnancy, with human chorionic gonadotropin (hCG) rising dramatically in early pregnancy and commonly associated with nausea and vomiting of pregnancy 1
• Cortisol and corticosterone production increases during pregnancy, with increased production of both free and bound cortisol due to elevated cortisol-binding globulin 1

Clinical Context: Nausea and Vomiting in Pregnancy

• Nausea and vomiting of pregnancy (NVP) affects 30-90% of pregnant women, typically beginning at 4-6 weeks gestation, peaking at 8-12 weeks, and subsiding by week 20 1
• Elevated hCG and estrogen levels, along with progesterone-mediated delayed gastric emptying, are implicated in the pathophysiology of NVP 1
• Early recognition and treatment of NVP may prevent progression to hyperemesis gravidarum, a severe condition requiring hospitalization 1

Morning Sickness as an Indicator of Viable Pregnancy at 6 Weeks

Evidence Supporting Morning Sickness as a Positive Prognostic Sign

• Morning sickness has been characterized in the medical literature as "an indicator of a healthy pregnancy" when discussing confounding factors in epidemiological studies, according to the Journal of Toxicology and Environmental Health - Part B: Critical Reviews 2
• If morning sickness is present at 6 weeks, this is a reassuring sign associated with lower miscarriage risk and suggests adequate hCG production, as noted in the Journal of Toxicology and Environmental Health - Part B: Critical Reviews 2