REFERENCE VALUES FOR SINGLETON AND TWIN PLACENTAL WEIGHTS

The largest series of normal singleton placental weights was collected in the Collaborative Perinatal Study between the years 1959 and 1966 but values for normal twin placental weights were not published. In ou r study we examined 787 singleton and 514 twin normal placentas. Place ntas with associated conditions known to affect the weights of placent as were excluded. After establishing the normal values for singleton a nd twin placental weights, we concluded that weight gain of twin place ntas appears to accelerate between 24 and 36 weeks but reaches a plate au after 37 weeks, whereas singleton placentas appear to gain weight m ore uniformly throughout gestation. The mean values of twin placental weights for each gestational age are less than double those of singlet on placental weights for the same duration of gestation. Our singleton and twin placentas are heavier than those from previously published d ata and may reflect a generational or nutritional change over the 30 y ears since the original numbers were compiled.