Recurrence risk in hyperemesis gravidarum

Objectives To compare the risk of hyperemesis gravidarum in second pregnancies in women with and without hyperemesis in their first pregnancy, and to determine if this risk changes with changes in paternity or with the interval between deliveries. Design Cohort study. Setting Data from the population-based Medical Birth Registry of Norway, 1967-4998. Sample All women in the registry with records of their first and second singleton delivery, a total of 547,238 women. Methods The relative risk of hyperemesis in the second delivery was estimated as odds ratios (ORs) in logistic regression models, controlling for potential confounding factors. Main outcome measures The main outcome measure was the risk of hyperemesis in the second pregnancy according to hyperemesis in the first pregnancy, interval between deliveries and change in paternity. Results The risk of hyperemesis was 15.2% in the second pregnancy in women with and 0.7% in women without previous hyperemesis [OR = 26.4, 95% confidence interval (CI) 24.2, 28.7]. The OR did not change after adjustment for maternal age, change in paternity, period of the first delivery and time interval between deliveries. After a change in paternity, the risk of recurrent hyperemesis was 10.9% compared with 16.0% in women without a change in paternity [adjusted OR (aOR) = 0.60, 95% CI 0.39, 0.92]. The risk of hyperemesis in the second pregnancy increased with increasing time interval between deliveries, but only in women with no previous hyperemesis. Conclusions The primary finding was the high risk of recurrence observed in women with hyperemesis in the first pregnancy. The risk was reduced by a change in paternity. For women with no previous hyperemesis, a long interval between births slightly increased the risk of hyperemesis in the second pregnancy. Further studies are needed to explore the relative impact of genetic and environmental factors and their possible interactions in hyperemesis gravidarum.