Maternal volume homeostasis in early pregnancy in relation to fetal growth restriction.

Objective: To test the hypothesis that volume adaptation in pregnancies complicated by fetal growth restriction (FGR) is already abnormal very early in pregnancy.
Methods: In six pregnancies later complicated by FGR, volume homeostasis in the first 8 weeks was compared to that in ten normal pregnancies. Creatinine clearance, volume-dependent hormones, hemodilution-related variables, and ultrasonic cardiovascular dimensions were measured weekly between weeks 5 and 10, in the second and third trimesters, and postpartum. Differences between the two groups were analyzed by nonparametric tests.
Results: Very early in pregnancy, pregnancies complicated by FGR differed from normal pregnancies in the following ways: smaller left atrial diameter, smaller collapsible part of the inferior vena cava, lower serum sodium concentration, and smaller fall in serum creatinine and urea.
Conclusion: Fetal growth restriction is preceded by defective volume adaptation very early in pregnancy. It appears that the maternal compensation mechanisms are unable to resolve the transient state of vascular underfill seen in this period in normal gestation.