Associations Between Maternal Thyroid Function and Birth Outcomes in Chinese Mother-Child Dyads: A Retrospective Cohort Study

Association between maternal and cord blood thyroid hormones, and urine iodine concentration with fetal growth

OBJECTIVES

We planned to evaluate the association of fetal and maternal thyroid hormones and maternal iodine status with neonates' anthropometric parameters.

METHODS

In this cross-sectional study, levels of thyrotropin were measured in maternal serum in the first trimester of pregnancy, and thyrotropin (TSH) and free thyroxin (fT4) were measured in cord blood serum samples at birth. Urinary iodine concentration (UIC) levels in random urine samples of mothers were measured in the third trimester of pregnancy. The relationship between UIC and thyroid hormone levels of mothers with neonates' anthropometric birth parameters of neonates was evaluated.

RESULTS

One hundred eighty-eight mother-newborn pairs completed the study. Mean (SD) of cord blood TSH (CB-TSH), cord blood-free thyroxin (CB-FT4) values, and maternal TSH (M-TSH) levels were 8.8 (7.3) mIU/L, 1.01 (0.2) ng/dL, and 2.2 (0.9) mIU/L, respectively. After adjusting for confounders, there was a positive significant association between female neonate length and maternal TSH and log log-transformed CB TSH (LN_CB-TSH) (p<0.05). Median UIC (Q1-Q3) was 157 (53-241) μg/L, and there was no association between birth weight, birth length, and head circumferences of neonates and mothers' UIC (p>0.05).

CONCLUSIONS

We found a positive correlation between maternal TSH in the first trimester of pregnancy and the birth length of newborns, and a negative correlation was observed between CB-TSH and birth length in girls, but it did not provide conclusive evidence for the relationship between maternal and neonatal thyroid hormone levels and birth weight. There was no association between maternal UIC levels in the third trimester and birth anthropometric parameters.

Effect of Iodine Nutrition Status on Thyroid Function and Pregnancy Outcomes

Iodine is essential for normal thyroid function, supporting healthy fetal and child development. The relevance between maternal iodine nutrition status and pregnancy outcomes remains controversial. The aim was to explore whether urinary iodine concentrations (UIC)/urinary creatinine (UCr) was associated with thyroid function and adverse pregnancy outcomes. This study was performed in the Department of Endocrinology and Metabolism of the First Affiliated Hospital of Nanjing Medical University. A total of 212 pregnant women were enrolled from May 2018 to November 2021, from the first visit until postpartum. Maternal serum samples were obtained in the second half of pregnancy, and then thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), UIC, and UCr were tested. The correlation of UIC/UCr, which represented maternal iodine nutrition status, with TSH, FT4, and FT3 was studied using linear regression. And we assessed associations between UIC/UCr and pregnancy outcomes. Notably, we explored consistency between UIC/UCr and the incidence of low birth weight (LBW) by application of logistic regression analysis. A total of 212 women were divided into 3 groups according to the upper and lower quartiles of UIC/UCr. There were 53 women in group 1 (UIC/UCr < 106.96 ug/g), 106 women in group 2 (UIC/UCr 106.96-259.08 ug/g), and 53 women in group 3 (UIC/UCr > 259.08 ug/g). The level of UIC/UCr had a negative correlation with FT4 (r =  - 0.139, p = 0.043) but a positive correlation with TSH (r = 0.096, p = 0.162 > 0.05). There was a significant difference in the incidence of LBW among the 3 groups (p = 0.007). Logistic regression analysis found that the level of UIC/UCr was an independent factor for LBW (p = 0.048, OR = 0.991, 95%CI (0.982, 0.999)). The receiver operating characteristic (ROC) curve showed that the area under the curve (AUC) for UIC/UCr predicting the incidence of low birth weight was 0.687 (p = 0.013, 95%CI 0.575, 0.799). Lower UIC/UCr during pregnancy was associated with higher FT4 and lower TSH. And iodine deficiency during pregnancy is a risk factor for low birth weight. Our findings indicated that more attention should be paid to the appropriate iodine nutrition status in pregnant women, which can help prevent suffering from adverse pregnancy outcomes.

Maternal Thyroid Function and Birth Weight in Twins

CONTEXT

Thyroid hormones are associated with birth weight in singleton pregnancy. Twin pregnancies need more thyroid hormones to maintain the normal growth and development of the fetuses compared with single pregnancy.

OBJECTIVE

We aimed to investigate the association of thyroid hormones and birth weight in twins.

METHODS

This was a retrospective cohort study in a Chinese population. Pregnant women who received regular antenatal health care and delivered live-born twins from 2014 to 2019 were included (n = 1626). Linear mixed model with restricted cubic splines and logistic regression models were used to estimate the association of thyroid hormones with birth weight and birth weight discordance in twins.

RESULTS

We observed that both thyrotropin (TSH) and free thyroxine (FT4) were not associated with birth weight in twins overall, while when stratifying on fetal sex or chorionicity, there were nonlinear association between FT4 levels and birth weight in boys (Pnonlinear < .001) and in dichorionic (DC) twins (Pnonlinear = 0.03). Women with levels of FT4 lower than the 10th percentile had a higher risk of birth weight discordance in their offspring than women with normal FT4 levels (range, 2.5 to 97.5 percentiles) (odds ratio = 1.58; 95% CI, 1.05-2.33).

CONCLUSION

Our study suggests there was an association of FT4, but not TSH, with birth weight and birth weight discordance varied by sex and chorionicity. These findings could have implications for obstetricians to be aware of the importance of FT4 levels in preventing birth weight discordance in twin pregnancy.

Preconception TSH and Adverse Pregnancy Outcomes in China: A Nationwide Prospective Cohort Study

BACKGROUND

The relationship between maternal thyroid function and pregnancy outcomes remains controversial and the safe range of TSH is still unclear in women planning pregnancy.

METHODS

This population-based cohort study enrolled Chinese women who became pregnant in 30 provinces from 2010 to 2012 from the National Free Preconception Checkups Project. The maternal TSH level within 6 months before pregnancy and different pregnancy outcomes were collected and analyzed using restricted cubic spline regression model for dose-response relationship and potential optimal cutoff values. Logistic regression was used to reveal the relationship between different TSH groups and the risk of adverse outcomes.

RESULTS

Among 175 112 women, a J-shaped association was revealed between TSH and large for gestational age (LGA; P < 0.001). When TSH was lower than 1.27 or 0.91 mIU/L, lower TSH was associated with higher odds ratio of low birth weight (LBW; P = 0.003) or preterm delivery (P < 0.001). There was no significant association of preconception TSH with SGA, macrosomia, fetal anomalies, stillbirth, natural or induced abortion, and cesarean delivery. The range of TSH for odds ratio lower than 1.0 was within 0.91 to 1.82 mIU/L in dose-response association. Compared with TSH 0.91 to 1.82 mIU/L, TSH low (< 0.40 mIU/L and 0.40-0.90 mIU/L) and high (1.83-2.49 mIU/L, 2.50-3.99 mIU/L, and >4.00 mIU/L) were associated with higher risk of preterm delivery and LGA. There was no significant association between TSH groups and the risk of LBW except for TSH < 0.40 mIU/L.

CONCLUSION

Preconception TSH was associated with preterm delivery, LGA, and LBW. Preconception TSH had a bidirectional effect on LGA, indicating a potential mechanism regarding influence of TSH on birth weight. TSH within 0.91 to 1.82 mIU/L was the potential safe range for preconception women.