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Maternal obesity affects thyroid hormones in offspring
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Maternal alterations in thyroid hormone as well as neonatal changes are associated with maternal obesity, according to findings published in Clinical Endocrinology.
Fetal overgrowth and childhood obesity may be mediated by changes in free triiodothyronine levels in the offspring of obese mothers, according to the findings.
Melissa A. Suter, PhD, and colleagues from the department of obstetrics and gynecology at Baylor College of Medicine in Houston evaluated five groups of women based on weight as well as their offspring to determine the effect of maternal obesity on alterations in maternal and neonatal thyroid hormone levels. Women were divided into the following groups: normal weight (BMI, 18.5-24.9 kg/m2; n = 46), overweight (BMI, 25-29.9 kg/m2; n = 48), Obese 1 (BMI, 30-34.9 kg/m2; n = 49), Obese 2 (BMI, 35-39.9 kg/m2; n = 36) and Obese 3 (BMI, 40 kg/m2; n = 20).
Free T3, free thyroxine and thyroid-stimulating hormone levels were measured using matched maternal and neonatal serum samples.
Maternal and neonatal free T3 increased with increasing maternal obesity compared with normal weight. The Obese 2 and 3 groups experienced decreased maternal free T4 compared with normal weight. Neonatal free T4 increased in the overweight, Obese 1 and Obese 2 groups compared with normal weight. The Obese 2 and 3 groups had slightly increased TSH levels compared with normal weight; maternal TSH levels were unchanged. A significant positive correlation was found between maternal and neonatal free T3 levels (P < .001).
Compared with the normal weight group, maternal free T3 and free T4 ratio increased with increasing maternal obesity and neonatal free T3 and free T4 ratio only differed in Obese 1 and 3.
Compared with women with insufficient weight gain, excessive weight gain revealed significantly lower maternal free T4 levels (P = .013).
The infant’s birthweight was linked to maternal and neonatal free T3 and free T3 and free T4 ratios; no significant relationship was found between maternal and neonatal free T4 or TSH levels and birthweight.
“What is of notable interest in the current study is the lack of correlation between neonatal [free T4] and TSH, while [free T3] is tightly and significantly correlated between maternal and fetal serum levels,” the researchers wrote. “While [thyroid hormones] are essential for fetal development throughout gestation, the fetus has fully functioning thyroid gland by the midpoint of gestation. By term, it is believed that fetal [thyroid hormone] levels are being maintained by the fetus’ own hypothalamic-pituitary-thyroid axis. Therefore, the extent to which maternal [thyroid hormone] levels influence fetal levels remains to be determined.” – by Amber Cox
Disclosure: The researchers report no relevant financial disclosures.
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