Weights of Fetal Membranes and Umbilical Cords: Correlation With Placental Pathology.

Introduction: Proper placental gross examination requires weighing the placental disc trimmed of fetal membranes and the umbilical cord. However, untrimmed placental weights are often reported, both in cases submitted for consultation and in publications. Thus, determining the contribution of membranes and cords to untrimmed placental weights would be helpful in estimating the true trimmed weight of placentas. We sought to report the average weights of membranes and cord in term placentas and to correlate these weights with common placental pathologies.
Methods: A total of 500 consecutive placentas delivered between 36 and 42 weeks gestational age were subjected to a modified grossing protocol, in which the weight of the trimmed and untrimmed placentas, fetal membranes, and umbilical cords were recorded. Acute chorioamnionitis, meconium, maternal vascular malperfusion, and fetal vascular malperfusion were included as pathologic correlates. Clinical data such as the presence of fetal hydrops, intrauterine growth restriction, intrauterine fetal demise, and maternal diabetes were also recorded.
Results: The mean weights of the trimmed placenta, fetal membranes, and umbilical cords were 442 g (180-805 g), 47.2 g (16-108 g), and 37.9 g (9-126 g), respectively. The fetal membranes and umbilical cord weights contributed a mean of 16% to the total untrimmed placental weight. Meconium was associated with heavier fetal membranes. Fetal vascular malperfusion was associated with longer umbilical cord and thus also with heavier umbilical cords. Maternal vascular malperfusion and intrauterine growth restriction were associated with lighter placentas.
Discussion: The trimmed placental disc weight may be estimated by subtracting 16% (ie, weight of the fetal membranes and umbilical cord) from the untrimmed placental weight, or alternatively by subtracting the mean weight of the membranes and umbilical cord. It is important to consider the effects of meconium, fetal and maternal vascular malperfusion, and intrauterine growth restriction on membrane and cord weights when estimating the trimmed placental disc weight.