Physiological adaptation of maternal plasma volume during pregnancy: a systematic review and meta-analysis

Objective To describe the physiological pattern of gestational plasma volume adjustments in normal singleton pregnancy and compare this with the pattern in pregnancies complicated by pregnancy-induced hypertension, pre-eclampsia or fetal growth restriction. Methods We performed a meta-analysis of the current literature on plasma volume adjustments during physiological and complicated pregnancies. Literature was retrieved from PubMed (NCBI) and EMBASE (Ovid) databases. Included studies reported both reference plasma volume measurements (non-pregnant, prepregnancy or postpartum) and measurements obtained during predetermined gestational ages. Mean differences between the reference and pregnancy plasma volume measurements were calculated for predefined intervals of gestational age using a random-effects model described by DerSimonian and Laird. Results Thirty studies were included in the meta-analysis with publication dates ranging from 1934 to 2007. Plasma volume increased in the first weeks of pregnancy, with the steepest increase occurring during the second trimester. Plasma volume continued to increase in the third trimester with a pooled maximum increase of 1.13L (95% CI, 1.07-1.19 L), an increase of 45.6% (95% CI, 43.0 - 48.1%) in physiological pregnancies compared with the reference value. The plasma volume expansion in gestational hypertensive and growth-restricted pregnancies was 0.80L (95% CI, 0.59-1.02 L), an increase of 32.3% (95% CI, 23.6 - 41.1%) in the third trimester, a smaller increase than in physiological pregnancies (P < 0.0001). Conclusions During physiological pregnancy, plasma volume increases by, on average, more than 1L as compared with non-pregnant conditions. In pregnancies complicated by pregnancy-induced hypertension, pre-eclampsia or fetal growth restriction, plasma volume increase in the third trimester is 13.3% lower than in normal pregnancy. Copyright (c) 2016 ISUOG.