Fertility in women with type 1 diabetes - A population-based cohort study in Sweden

OBJECTIVE - The purpose of this study was to assess fertility in women with type 1 diabetes and the risk of congenital malformations in their offspring. RESEARCH DESIGN AND METHODS - This was a register-based cohort study in Sweden. All 5,978 women hospitalized for type -1 diabetes at age :516 years identified in the Swedish Inpatient Register during 1965-2004 were followed until the end of 2004 through linkage to nationwide registers. A standardized fertility ratio (SFR), the ratio of observed to expected number of live births, with 95% Cls, was used to express the relative fertility rate. The proportion of newborns with congenital malformations was compared with that of the general population. RESULTS - We observed 4,013 live births (SFR 0.80 [95% CI 0.77-0.82]). The SFRs for those who had retinopathy, nephropathy, neuropathy, or cardiovascular complications were 0.63, 0.54, 0.50, and 0.34, respectively. Stratified analyses by year of first hospitalization showed that the reduced fertility was confined to women first hospitalized before 1985, but the presence of complications was associated with subfertility in all calendar-year strata. The proportions of newborns with congenital malformations decreased from 11.7% during 1973-1984 to 6.9% during 1995-2004 but were consistently higher than the corresponding figures for the general population. CONCLUSIONS - Women with type 1 diabetes have reduced fertility, but it appears that normalization has occurred among women with uncomplicated disease and an onset in the past 20 years. Our results suggest that the stricter metabolic control exercised in the past 20 years may have helped prevent subfertility. However, although the risk of congenital malformations has decreased, it is still higher than that for the general population.