LAUSR

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.