Intergenerational exchange and perinatal risks: a note on interpretation of generational recurrence risks.

Population-based data that cover reproductive health outcomes across two complete generations have recently become available in the Nordic countries. Such data enable estimation of recurrence risks from one generation to the next of different conditions such as birth defects or pre-eclampsia. Risks related to a singleton pregnancy involve the contribution of three individuals: the mother, the father and the fetus. A paternal contribution is mainly through the father's contribution of half of the alleles of the fetus. A maternal contribution may occur in three fundamentally different ways. First, the mother provides half of the genomic alleles to the fetus, with contribution of paternal alleles completing the whole genome. Second, the mother provides the fetal environment and possible susceptibility to complications during pregnancy which she may have inherited from her mother. Finally, she provides the fetal mitochondria. Because of these different contributions, recurrence from mother to offspring is fundamentally different from recurrence from father to offspring. How recurrence risks reflect and shape the underlying contributions to overall perinatal risk is illustrated through a review of published data from Norway on gestational age, pre-eclampsia and birth defects.