Subclinical Changes in Maternal Thyroid Function Parameters in Pregnancy and Fetal Growth.

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Subclinical Changes in Maternal Thyroid Function Parameters in Pregnancy and Fetal Growth.

J Clin Endocrinol Metab. 2017 Dec 26;:

Authors: Johns LE, Ferguson KK, Cantonwine DE, Mukherjee B, Meeker JD, McElrath TF

Abstract
Context: Overt thyroid disease in pregnancy is a known risk factor for abnormal fetal growth and development. Data on the effects of milder forms of variation in maternal thyroid function on intrauterine growth are less well examined.
Objective: We aimed to explore these associations using repeated thyroid hormone and ultrasound measurements.
Design, Setting, and Participants: Data were obtained from 439 pregnant women without diagnosed thyroid disease who were participants in a case-control study of preterm birth nested within an ongoing prospective birth cohort in Boston, MA.
Main Outcome Measures: Ultrasound and delivery indices of fetal growth were standardized to those measured in a larger population.
Results: At median 10, 18, and 26 weeks of gestation, we observed significant inverse associations between FT4 and birth weight z-scores, with the strongest association detected at median 10 weeks. At this time point, a 10 percent increase in FT4 was associated with a 0.02 z-score decrease (approximately 8.5 grams) in birth weight (β = -0.41 for ln-transformed FT4; 95% confidence interval [CI] = -0.64, -0.18). FT4 was also inversely associated with repeated measurements of estimated fetal weight, head circumference, and abdominal circumference. Birth weight did not statistically significantly differ between women with subclinical hypothyroidism (N=10) and those without (N=426). We observed weaker inverse associations for total T4 and a positive relationship between total T3 and birth weight z-scores. We did not observe any associations for TSH.
Conclusion: In pregnant women without overt thyroid disease, subclinical changes in thyroid function parameters may influence fetal growth.

PMID: 29293986 [PubMed - as supplied by publisher]

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