Fetal-Placental Weight Relationships in the Rhesus (Macaca mulatta)

Abstract

Several hundred timed Macaca mulatta pregnancies, delivered by caesarean section near term, provided data to derive statistical parameters of fetal-placental weight relationships. About 25% of placentas were of the single disc type while the remainder were bidiscoid. Placentas of male infants, regardless of type, were heavier than those of female infants and double disc placentas were heavier than single disc placentas. Birth weights of male infants with double disc placentas were greater than those of female infants, while birth weights of males and females with single disc placentas were the same. However, these differences were not statistically significant. Fetal and placental weights were highly correlated (r = 0.64). The fetal-placental ratio increased as gestation increased and at term was 3.5. These findings are similar to observations made in the human and provide a basis for use of the rhesus as an experimental model.