The velocity of fetal growth is associated with the breadth of the placental surface, but not with the length.

Studies of the placenta in pregnancies complicated by pre-eclampsia have led to the suggestion that tissue along the length and breadth of its surface has different functions. A recent study in Saudi Arabia showed that the body size of newborn babies was related to the breadth of the surface at birth but not to its length. We have now examined whether the association between placental breadth and body size reflects large size of the baby from an early stage of gestation or rapid growth between early and late gestation. We studied 230 women who gave birth to singleton babies in King Khalid Hospital, Riyadh, Saudi Arabia. In total, 176 had ultrasound measurements both before 28 weeks and at 28 weeks or later, which we define as early and late gestation. We used these to calculate growth velocities between early and late gestation, which we expressed as the change in standard deviation scores over a 10-week period. The breadth of the placental surface was correlated with fetal growth velocity. The correlation coefficients were 0.24 (P = 0.002) for the head circumference, 0.24 (P = 0.001) for the biparietal diameter and 0.34 (P < 0.001) for the abdominal circumference. The length of the surface was not related to fetal growth velocity. Tissue along the breadth of the placental surface may be more important than tissue along the length in the transfer of nutrients from mother to baby. This may be part of a wider phenomenon of regional differences in function across the placental surface.