EP08.33: Placental volume relative to fetal volume at 27 weeks of gestation and subsequent fetal growth

Since placenta is fundamental for fetal growth, it is conceivable that placenta relative to fetal size (ratio) in mid-pregnancy is an indicator of the growth potential of the fetus. Thus, we aimed to study the association of ratio at gestational week (GW) 27 with fetal growth until GW 37. We also studied whether the ratio affects fetal growth differently according to the size of the fetus at GW 27. In a convenience sample of 86 singleton pregnancies, we measured placental and fetal volume by magnetic resonance imaging (MRI) at GW 27, and fetal volume at GW 37. The association of ratio (placental volume/fetal volume) at GW 27 with fetal growth (fetal volume GW 37-fetal volume GW 27) was estimated by linear regression, and adjustment was made for time interval (in days) between the MRI measurements. To explore whether an association of ratio with fetal growth was independent of fetal size, we studied average fetal growth per day among the one third smallest fetuses (n = 28) and the one third largest fetuses (n = 28) with the one third lowest and one third highest ratio. There was a strong positive association of ratio at GW 27 with fetal growth until GW 37 (p = 0.002). Among the one third smallest fetuses, average fetal volume increase per day was 21.39 (standard deviation (SD) 2.8) cm3 if the ratio was low, and 24.46 (SD 3.6) cm3 if the ratio was high. Among the large fetuses, the average increase in volume per day was 26.86 (SD 1.7) cm3 if the ratio was low, and 28.63 (SD 4.5) cm3 if the ratio was high. The small fetuses grew relatively more if the ratio was high as compared to if ratio was low (206% vs 181%). For the large fetuses, the relative growth was independent of the ratio at GW 27 (166% vs 162%). Placental volume relative to fetal volume at GW 27 were positively associated with subsequent fetal growth. Possibly, ratio is an indicator of fetal growth potential, particularly among small fetuses.