The effect of parity on placental weight and birth weight: interaction with placental alkaline phosphatase polymorphism.
The effect of parity on placental weight and birth weight is examined through a series of birth records from an Indian population in Calcutta. Placental weight and birth weight increase with parity, the maximum increment occurring between parities 1 and 2. This is compatible with a hypothesis of sensitization of the mother to foetal, paternally derived, antigens. The three common placental alkaline phosphatase enzymic genotypes have no effect on determining foetal development.