Recurrence of hyperemesis gravidarum across generations: population based cohort study

OBJECTIVE To estimate the risk of hyperemesis gravidarum (hyperemesis) according to whether the daughters and sons under study were born after pregnancies complicated by hyperemesis. DESIGN Population based cohort study. SETTING Registry data from Norway. PARTICIPANTS Linked generational data from the medical birth registry of Norway (1967-2006): 544 087 units of mother and childbearing daughter and 399 777 units of mother and child producing son. MAIN OUTCOME MEASURE Hyperemesis in daughters in mother and childbearing daughter units and hyperemesis in female partners of sons in mother and child producing son units. RESULTS Daughters who were born after a pregnancy complicated by hyperemesis had a 3% risk of having hyperemesis in their own pregnancy, while women who were born after an unaffected pregnancy had a risk of 1.1% (unadjusted odds ratio 2.9, 95% confidence interval 2.4 to 3.6). Female partners of sons who were born after pregnancies complicated by hyperemesis had a risk of 1.2% (1.0, 0.7 to 1.6). Daughters born after a pregnancy not complicated by hyperemesis had an increased risk of the condition if the mother had hyperemesis in a previous or subsequent pregnancy (3.2 (1.6 to 6.4) if hyperemesis had occurred in one of the mother's previous pregnancies and 3.7 (1.5 to 9.1) if it had occurred in a later pregnancy). Adjustment for maternal age at childbirth, period of birth, and parity did not change the estimates. Restrictions to firstborns did not influence the results. CONCLUSIONS Hyperemesis gravidarum is more strongly influenced by the maternal genotype than the fetal genotype, though environmental influences along the maternal line cannot be excluded as contributing factors.