The association between fetal development and neonatal survival and preceding pregnancies of the mother would be compatible with the action of male and female specific antigens capable of affecting selective implantation of blastocysts, which commands subsequent fetal development as well as early neonatal survival.

7,773 placentae of newborns were analyzed in order to test a hypothesis of specific immunological concepto-maternal interactions due to maleness and occurring during normal pregnancy. An association between placental weight of newborn male and the sex of conceptuses of previous pregnancies was found which supports the hypothesis. No such an association was found for female newborn. The confirmation of these results could open new avenues in the study of sex-differential survival of the conceptus throughout gestation.

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26Introduction: Following the investigation of the mother's preceding pregnancies on fetal 27

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