[Intrauterine selection and human ABO incompatibility. II. Analysis of blood group distribution among 3652 families]

Significant deviations in distribution of compatible and incompatible offspring comparing with expected were discovered in incompatible matings 0XA, 0XB, AXB, BXA. These deviations were not significant in control group of matings AX0, BX0, AXA, BXB. The following phenomenon was observed in rhesus-positive mother with normal pregnancies in incompatible matings: primigravidae in the age group of 25 years and younger had the excess of incompatible children by 24.5% (p < 0.01), multigravidae of the same age group had the excess of compatible children by 59.1% (p < 0.001), multigravidae in the age group of 26 years and older had the excess of imcompatible children by 24.1% (p < 0.01). Thus, the contrary vectors of selection act in the population, and on the whole the effects of selection may be masked because of different directions of these vectors.