Endocrine Abstracts

Context: In the background population, maternal TSH levels >2.5 mUI/l in late pregnancy have been reported to be associated with breech presentation. This has not been addressed in women treated with levothyroxine.

Aim: Our aim was to study the relationship of 3rd trimester maternal TSH with caesarean section (CS) due to foetal malposition in pregnant women treated with levothyroxine since before pregnancy.

Methods: We have studied 222 women with primary pregestational hypothyroidism or differentiated thyroid carcinoma treated with levothyroxine since before pregnancy and delivering at a gestational age of 22 weeks or more. Women with pregestational diabetes mellitus and multiple pregnancies were excluded. As potential predictors of CS due to malposition we have considered 3rd maternal TSH, maternal age, BMI classification, nulliparity, gestational age at delivery, foetal sex, birth weight, small/adequate/large weight for gestational age, and major malformations. Statistical analyses: data are expressed as percentage or median (P25, P75), analyses include a logistic regression analysis with CS due to foetal malposition as the dependent variable and using all the previously mentioned potential predictors.

Results: Maternal characteristics were: age 33 (30–36) years, prepregnancy BMI 23.33 (21.4–23.8) kg/m², mean 3rd trimester TSH 1.5 (0.3–2.6). The most frequent underlying diseases were hypothyroidism (50%), hypothyroidism after treatment for Graves’ disease (27.6%) and post-surgery differentiated thyroid carcinoma (15.3%). The rate of CS due to foetal malposition was 2.7%. Logistic regression analysis to predict CS due to foetal malposition identified 3rd trimester maternal TSH and maternal underweight as potential predictors, with odds ratios of 1.29 (1.1–1.5) and 13.9 (1.17–165.5) respectively.

Conclusions: In women receiving pregestational treatment with levothyroxine, maternal 3rd trimester TSH and underweight are predictors of CS due to foetal malposition. This extends the findings in the general obstetric population.