Decreased birth weight, length, and head circumference in children born by women years after treatment for hyperthyroidism.

CONTEXT: Whether hyperthyroidism influences the birth characteristics of children born several years after treatment is unknown.

OBJECTIVE

The objective of the study was to compare birth characteristics in singleton newborns delivered by women previously treated for Graves' disease (GD), toxic nodular goiter (TNG), or nontoxic goiter (NTG).

DESIGN

This was a nested case-control design within a national cohort registry study from 1950 through 2006.

SETTING

The study was conducted at a university and a hospital center in collaboration.

PATIENTS: The birth characteristics of newborns (n = 3421) delivered in a cohort of 43 633 women treated for GD or toxic nodular goiter by radioiodine or surgery (exposed group) at least 1 year prior to pregnancy were compared with newborns (n = 2914) of 45 655 mothers, previously operated for NTG (unexposed group).

MAIN OUTCOME: The primary outcome was birth weight, length, and head circumference. The secondary outcome was malformations, gestational age, and type of hyperthyroidism.

RESULTS

The birth weight of exposed children was 3431 ± 607 g (mean ± SD) compared with the unexposed, 3520 ± 641 g (P < .001). The cumulative odds ratio (OR) for lower birth weight was 1.29 [95% confidence interval (CI) 1.16-1.43]. The average birth length for the exposed children was 50.0 ± 2.7 cm compared with the unexposed of 50.4 cm ± 2.6 cm (P < .01) [cumulative OR 1.25 (95% CI 1.13-1.37)]. The head circumference was 34.5 ± 1.9 cm among exposed and 34.7 ± 1.8 cm, respectively (P < .001), with an OR of 1.24 (95% CI 1.13-1.35). No differences in birth characteristics were observed between children born after maternal GD or toxic nodular goiter.

CONCLUSIONS

Previous GD or TNG may influence the birth characteristics several years after radioiodine or surgical treatment.