Maternal cardiac adaptation and fetal growth

BACKGROUND: Pregnancies with small for gestational age fetuses are at increased risk of adverse maternal-fetal outcomes. Previous studies examining the relationship between maternal hemodynamics and fetal growth were mainly focused on high risk pregnancies and those with fetuses with extreme birthweights such as less than the 3rd or 10th percentile and assumed a similar growth pattern in fetuses above the 10th percentile throughout gestation.

OBJECTIVE: To evaluate the trends in maternal cardiac function, fetal growth and oxygenation with advancing gestational age in a routine obstetric population and all ranges of birthweight percentiles.

STUDY DESIGN: This was a prospective, longitudinal study assessing maternal cardiac output and peripheral vascular resistance by bioreactance at 11+0-13+6, 19+0-24+0, 30+0-34+0 and 35+0-37+0 weeks' gestation, sonographic estimated fetal weight in the last three visits and the ratio of the middle cerebral artery by the umbilical artery pulsatility indices or cerebroplacental ratio in the last two visits. Women were divided into five groups according to birthweight percentile: Group 1 <10th percentile (n=261); group 2, 10-19.9 percentile (n=180), group 3, 20-29.9 percentile (n=189); group 4, 30-69.9 percentile (n=651) and group 5, >70th centile (n=508). Multilevel linear mixed-effects model was performed to compare the repeated measures of hemodynamic variables and z-scores of estimated fetal weight and cerebroplacental ratio.

RESULTS: In visit 2, compared to visit 1, in all groups cardiac output increased and peripheral vascular resistance decreased. At visit 3, groups 1, 2 and 3, compared to 4 and 5, demonstrated an abrupt decrease in cardiac output and increase in peripheral vascular resistance. From visit 2, group 1 had a constant decline in estimated fetal weight, coinciding with the steepest decline in maternal cardiac output and rise in peripheral vascular resistance. In contrast, in groups 4 and 5 the estimated fetal weight had a stable or accelerative pattern, coinciding with the greatest increase in cardiac output and lowest peripheral vascular resistance. Groups 2 and 3 showed a stable growth pattern with intermediate cardiac output and peripheral vascular resistance. Increasing birthweight was associated with higher cerebroplacental ratio. Groups 3,4 and 5 had stable cerebroplacental ratio across visits 3 and 4, whilst groups 1 and 2 demonstrated a significant decline.

CONCLUSION: in a general obstetric population, maternal cardiac adaptation from 32 weeks' gestation parallels the pattern of fetal growth and oxygenation; babies with birthweight <20th percentile have progressive decline in fetal cerebroplacental ratio, decline in maternal cardiac output and increase in peripheral vascular resistance.