Searchable abstracts of presentations at key conferences in endocrinology
Endocrine Abstracts (2011) 26 OC1.1

1Department of Internal Medicine, Erasmus MC, Rotterdam, The Netherlands; 2The Generation R Study Group, Erasmus MC, Rotterdam, The Netherlands; 3Department of Obstetrics and Gynaecology, Erasmus MC, Rotterdam, The Netherlands; 4Department of Epidemiology, Erasmus MC, Rotterdam, The Netherlands; 5Department of Clinical Chemistry, Erasmus MC, Rotterdam, The Netherlands; 6Department of Child and Adolescent Psychiatry, Erasmus MC, Rotterdam, The Netherlands.


Introduction: Maternal hypo- and hyperthyroidism during pregnancy have been associated with high and low birth weights, which predispose for various diseases later in life, such as cardiovascular diseases and cancer. However, the effects of variation in maternal thyroid hormone levels within the normal range on fetal growth and birth weight are largely unknown.

Methods: First trimester serum TSH, FT4 and TPO-antibody (TPOab) levels were determined in 4950 pregnant Caucasian women from a population-based cohort study. Fetal weight was estimated in late pregnancy by ultrasound. In 4469 subjects with normal range TSH and FT4 levels, the effects of TSH, FT4 and TPOab levels on fetal and birth weight were studied.

Results: No associations of maternal TSH levels with either fetal or birth weight were detected. Higher maternal FT4 levels were associated with both lower weight in late pregnancy (Plin<0.001) and at birth (Plin<0.0001). In mothers with FT4 levels in the highest quintile (17.0–21.9 pmol/l), late pregnancy fetal weight was 22.8±8.7 (mean±S.E.M.) g (P=0.009) and birth weight 75.5±21.1 g (P<0.001) lower compared to the lowest quintile (10.3–12.9 pmol/l).

In mothers with TPOabs in the highest quartile of the detectable range (>8.9 IU/ml), birth weight was 55.8±20.7 g (P=0.007) higher compared to the group without TPOabs, which remained significant after adjusting for TSH and FT4 levels. No association with late pregnancy fetal weight was detected.

Conclusions: We show that high-normal FT4 levels in the first trimester are associated with a substantially lower birth weight. We additionally show that higher TPOab levels are associated with higher birth weights, even after adjusting for TSH and FT4 levels. These data demonstrate that even mild variation in thyroid function within the normal range can have important fetal consequences, and underline the importance of tight regulation of maternal thyroid hormone levels during pregnancy.

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