Women with high levels of thyroid-stimulating hormone during pregnancy may experience greater early pregnancy weight gain and total gestational weight gain compared with women with lower levels of the hormone, according to study data.
Romy Gaillard, MD, PhD, of the Generation R Study Group, Erasmus University Medical Center, the Netherlands, and colleagues evaluated data from the Generation R Study on 5,726 pregnant women (mean age, 29.7 years) to determine the associations between maternal thyroid function in early pregnancy and maternal BMI and weight gain during pregnancy.
Maternal TSH and free thyroxine levels were measured at 13.5 weeks’ gestation, and maternal weight was assessed before pregnancy and in each trimester.
Median values were 1.4 mIU/L for TSH and 14.8 pmol/L for free T4, and the reference ranges were 0.03 mIU/L to 4.04 mIU/L for TSH and 10.4 pmol/L to 22 pmol/L for free T4. Mean prepregnancy BMI was 24.5 kg/m2; mean total weight gain during pregnancy was 15.2 kg.
In early pregnancy, higher maternal TSH was associated with lower risk for maternal pregnancy underweight (P < .05) and higher risk for excessive gestational weight gain (OR = 1.28; 95% CI, 1.13-1.45 per standard deviation [SD] increase in maternal TSH level) compared with lower maternal TSH. Higher maternal free T4 was associated with higher risk for pregnancy underweight, lower risk for prepregnancy overweight (OR = 1.3; 95% CI, 1.15-1.46) or obesity (OR = 0.83; 95% CI, 0.75-0.92) and lower risk for excessive gestational weight gain (OR = 0.83; 95% CI, 0.73-0.94 per SD increase in maternal free T4 level) compared with lower maternal free T4.
After adjustment for sociodemographic and lifestyle-related characteristics, higher maternal TSH was associated with higher maternal prepregnancy BMI (difference, 0.18 kg/m2 per SD increase in TSH level), higher total gestational weight gain (difference, 0.02 kg per week per SD increase in TSH level) and higher early pregnancy weight gain (difference, 0.03 kg per week per SD increase in TSH level) compared with lower maternal TSH. No relationship was found between maternal TSH level and late pregnancy weight gain.
In the basic model, adjusted for gestational age at thyroid measurement, higher maternal free T4 was associated with lower prepregnancy BMI (difference, –0.54 kg/m2 per SD increase in free T4 level), lower total gestational weight gain (difference, –0.02 kg per week per SD increase in free T4 level) and lower early pregnancy weight gain (difference, –0.04 kg per week per SD increase in free T4 level) compared with lower maternal free T4 levels.
Maternal hypothyroidism was associated with higher prepregnancy BMI, and hyperthyroidism was associated with a lower prepregnancy BMI compared with normal thyroid function, according to the findings. Early pregnancy weight gain was higher with maternal hypothyroidism and lower with maternal hyperthyroidism compared with normal thyroid function. – by Amber Cox
Disclosures: The researchers report no relevant financial disclosures.