VP34.03: Is there an association between the size of the decline in maternal cardiac output in the third trimester and offspring birthweight?

Abstract

Maternal cardiac output (CO) typically declines in late pregnancy, which seems paradoxical given the fetus' steadily increasing oxygen and nutrient demands in this period. Higher maternal CO in the second half of pregnancy has previously been associated with higher birthweight, but whether changes in CO in the last months of pregnancy are associated with birthweight is unknown. We assessed associations between overall CO level in the third trimester, changes in CO, and offspring birthweight. Using the USCOM-1A device, we measured CO in gestational weeks 27-30, 34-36, and biweekly thereafter until delivery in 365 healthy pregnant women without hypertensive disorders of pregnancy or diabetes. Using a joint model, we modelled log(CO) as a function of gestational age (linear mixed model) and offspring birthweight as a function of a woman's personal third trimester level of CO taken from the mixed model (multiple linear regression). Birthweight was expressed as 1) a z-score and 2) the deviation of birthweight z-score from the fetal weight z-score estimated mid-pregnancy (a proxy for fetal genetic growth potential). We also assessed the association between the percentage change in CO across the third trimester and offspring birthweight. Higher maternal CO levels were associated with higher birthweight z-scores after adjustment for maternal factors (β 1.27, 95% CI 0.49-2.05), corresponding to an increase of 0.23 in z-score for a CO increase from 5 to 6 L/min. The association was similar when using the deviation at birth from estimated fetal weight z-score mid-pregnancy as the outcome (adjusted β 1.39, 95% CI 0.58-2.20). The degree of decline in third-trimester CO was not significantly associated with birthweight z-score. A woman's personal overall CO level is a better determinant of birthweight than changes in CO during the third trimester.