OBJECTIVES: To evaluate the effect of preeclampsia (PE) and gestational hypertension (GH) on subsequent hypothyroidism. Recent studies suggest that women with PE have increased risk for reduced thyroid function, but the association between PE and GH with overt hypothyroidism has not been examined. STUDY DESIGN: Two prospective population-based cohort studies, the Northern Finland Birth Cohorts 1966 and 1986, followed women who had PE (N=955), GH (N=1449) or were normotensive (N=13531) during pregnancy. Finnish national registers were used to confirm subsequent hypothyroidism. Adjusted hazard ratios (aHRs) with 95% confidence intervals (CIs) estimated hypothyroidism risk when comparing women with PE or GH with normotensive women. MAIN OUTCOME MEASURES: Primary hypothyroidism during follow-up of 20-40 years. RESULTS: The subsequent prevalence of hypothyroidism was higher among women with PE (4.0%) and GH (4.5%) compared with normotensive women (3.5%), but the risk increase was not significant (aHR for PE 1.13, 95%CI 0.80-1.59 and aHR for GH 1.11, 95%CI 0.85-1.45). Subgroup analysis among nulliparous women revealed a significant association between late PE and subsequent hypothyroidism (aHR 1.82, 95%CI 1.04-3.19). Early or recurrent PE were not associated with hypothyroidism (aHR 0.93, 95%CI 0.46-1.81 and aHR 1.35, 95%CI 0.63-2.88, respectively). CONCLUSIONS: Overall, PE or GH during pregnancy was not significantly associated with subsequent hypothyroidism in Finnish women after 20-40 years of follow-up. However, late PE in nulliparous women was associated with a 1.8-fold increased risk of subsequent hypothyroidism, a finding that merits further study in other populations.
Keywords: gestational hypertension; hypothyroidism; preeclampsia; thyroid.