Placental volume at gestational week 27 and subsequent fetal growth: An observational study

Objectives

To study if placental volume and placental to fetal ratio at gestational week (GW) 27 correlate with subsequent fetal growth. We also investigated whether the 1/3 smallest and 1/3 largest fetuses have different growth potential depending on placental volume.

Methods

Placental and fetal volume was measured by magnetic resonance imaging (MRI) at GW 27 and 37 in 86 singleton pregnancies. Placental to fetal ratio was calculated as placental volume/fetal volume. Growth was calculated as [(fetal volume at GW 37 – fetal volume at GW 27)/number of days between the MRI examinations]. To explore whether a higher placental volume affected growth of small and large fetuses differently, we performed separate analyses of the 1/3 smallest and 1/3 largest fetuses with placental volume under and above the median at GW 27.

Results

We found a positive correlation of both placental volume and placental to fetal ratio at GW 27 with average growth velocity, r = 0.51 (p < 0.001) and r = 0.33 (p = 0.002) respectively. The correlation between fetal volume at GW 27 and average growth velocity was r = 0.48 (p < 0.001). The small fetuses had significantly lower average growth velocity if the placental volume was low compared to if the placental volume was high, 22 (SD 3) cm³/day versus 25 (SD 3) cm³/day, p = 0.02. Among the large fetuses, placental volume did not significantly affect growth.

Conclusions

Placental volume and placental to fetal ratio at GW 27 were positively correlated with subsequent fetal growth. Possibly, placental size is an indicator of fetal growth potential, especially among small fetuses.