MATERNAL PLASMA-VOLUME EXPANSION AND HORMONAL CHANGES IN WOMEN WITH IDIOPATHIC FETAL GROWTH-RETARDATION

Objective: To explore the mechanisms underlying the reduced maternal p lasma volume associated with idiopathic fetal growth retardation (FGR) . Methods: In 30 normotensive women with growth-retarded fetuses and 2 6 with normal-size fetuses, plasma volume was measured with a modified Evan's blue method. Plasma levels of atrial natriuretic peptide, plas ma renin activity, aldosterone, estradiol, and progesterone, and urina ry excretion of kallikrein, prostacyclin, and thromboxane A2 were meas ured at 34-40 weeks' gestation. Results: Compared with controls, gravi das with growth-retarded fetuses had a reduced plasma volume expansion (P < .01), similar atrial natriuretic peptide and plasma renin activi ty levels, and lower serum aldosterone (P < .001) and placental steroi ds (P < .03). These women also had decreased urinary kallikrein activi ty and prostaglandin excretion (P < .05). When both groups were combin ed, maternal plasma volume correlated significantly with birth weight (r = 0.53) and placental weight (r = 0.66). Conclusion: Normotensive w omen with idiopathic FGR have reduced plasma volume expansion. Althoug h the exact mechanisms of this change are unknown, we postulate that t he lower maternal aldosterone levels and reduced levels of vasodilator substances, such as prostacyclin and kallikrein, may have a causal ro le.