Assessing maternal thyroid function and its relationship to duration of the first stage of labor

INTRODUCTION: Maternal thyroid function plays a critical role in the normal labor process. Whether maternal thyroid function affects the duration of the first stage of labor is still unknown. METHODS: Maternal serum levels of free thyroxine (FT4), thyroid-stimulating hormone (TSH) and thyroid peroxidase antibody (TPOAb) were detected in 31,382 pregnant women. A multiple linear regression model was applied to investigate the effect of maternal thyroid function on the duration of the first stage of labor. RESULTS: FT4 level in the second trimester and in the third trimester was found to be negatively associated with duration of the first stage of labor (β = −1.30 h, 95% CI: −2.28, −0.32, P < 0.01; β = −0.35 h, 95% CI: −0.61, −0.10, P < 0.01). TSH level in the third trimester was found to be positively associated with the duration of the first stage of labor (β = 0.12 h, 95% CI: 0.06, 0.18, P < 0.001). Per unit increase in TPOAb (IU/mL) in the second trimester and in the third trimester was significantly associated with prolonged first stage of labor (β = 0.08 h, 95% CI: 0.01, 0.14, P = 0.02; β = 0.09 h, 95% CI: 0.02, 0.15, P = 0.01). For pregnant women suffering from subclinical hypothyroidism combined without TPOAb, TSH level in the third trimester exhibited a significant positive association with the length of the first stage of labor (β = 2.44 h, 95% CI: 0.03, 4.84, P = 0.04). CONCLUSIONS: These findings suggest that maternal FT4, TSH and TPOAb might be important predictors of the first stage of labor.