Maternal thyroid hormone concentration during late gestation is associated with foetal position at birth

Abstract

Objective: To evaluate whether there is an association between maternal thyroid hormone and foetal cephalic head position at term gestation. Context: Rotation and flexion of the head enables the foetus to negotiate the birth canal. Low-normal range thyroid hormone concentrations in euthyroid pregnant women constitute a risk of infant motor abnormality. We hypothesized that low normal maternal thyroid hormone levels are associated with increased risk of abnormal foetal position at delivery. Design: In 960 healthy Dutch women with term gestation and cephalic foetal presentation, thyroid parameters [foetal T4 (FT4), TSH and thyroid peroxidase antibody] were assessed at 36 weeks of gestation, and related to foetal head position (anterior cephalic vs. abnormal cephalic) and delivery mode (spontaneous vs. assisted delivery). Results: Women presenting in anterior position (n = 891) had significantly higher FT4 levels at 36 weeks of gestation than those with abnormal cephalic presentation (n = 69). There were no between-group differences for TSH. Regression analyses indicated that the risk of abnormal head position decreased as a function of increasing FT4 [single odds ratio (OR) = 0·87, 95% confidence intervals (CI) 0·77–0·98; multivariate OR = 0·88, 95% CI 0·72–0·99)]. A similar inverse relationship between maternal FT4 and risk of assisted delivery was obtained (OR = 0·86, 95% CI 0·79–0·95; OR = 0·91, 95% CI 0·84–0·98). Conclusion: The lower the maternal FT4 concentration at 36 weeks of gestation, the higher the risk of abnormal cephalic foetal presentation and assisted delivery.