Pregnancy rewrites the normal values

PREGNANCY REWRITES THE NORMAL VALUES

A value inside the nonpregnant reference range can be abnormal in a pregnant patient, and a value outside it can be exactly what you expect. The exam writes items on that gap. Learn the direction of each shift and the physiology that drives it, then get the number itself from Book 7.

VOLUME OUTRUNS CELLS

Plasma volume expands far more than red cell mass does. Both rise, but the plasma rises faster, so hemoglobin and hematocrit fall by dilution. A mild fall is physiologic hemodilution, not hemorrhage. Cardiac output rises, driven by both stroke volume and a resting heart rate that runs above the prepregnancy rate, while systemic vascular resistance falls, which is why blood pressure typically dips in the second trimester. The white cell count also rises in pregnancy and rises further during labor and the early postpartum period, so leukocytosis by itself is not evidence of infection.

CLEARANCE RISES, VENTILATION RISES

Renal plasma flow and glomerular filtration increase substantially, pulling serum creatinine and blood urea nitrogen down. A creatinine that would be entirely reassuring in a nonpregnant adult can signal renal involvement in preeclampsia. Progesterone drives an increase in tidal volume and minute ventilation, producing a chronic compensated respiratory alkalosis: PaCO2 sits low, and the bicarbonate falls to compensate. Read an arterial blood gas in pregnancy against the pregnant baseline or you will call a normal gas abnormal.

CLOTTING TIPS ONE WAY

Fibrinogen and several clotting factors rise while fibrinolytic activity falls. This protects against hemorrhage at delivery and, in the same motion, raises thromboembolic risk. That risk is highest in the postpartum weeks, not during pregnancy itself. Add the positional rule: after roughly twenty weeks the supine position lets the gravid uterus compress the inferior vena cava, dropping venous return, cardiac output, and uterine perfusion. Lateral tilt or left lateral positioning is a hemodynamic intervention, not a comfort measure, and it is part of resuscitation in a pregnant patient.

Watch outa normal creatinine may be an abnormal creatinine here. Interpret renal values against the lowered pregnant baseline.

Margin notethey test the value that looks fine. Every number → BOOK 07 · P4. Every infusion calculation → BOOK 06 · P3

Takeawayinterpret every value in a pregnant patient against the pregnant baseline, and know which physiologic change moved it.