Trimester-Specific Thyroid Function in Pregnant Women with Different Iodine Statuses

Abstract

Objectives: To explore trimester-specific thyroid function changes under different iodine statuses throughout pregnancy. Methods: A cross-sectional study was conducted to assess the pregnancy iodine status, and 2,378 healthy pregnant women covering all 3 trimesters were recruited. Urinary iodine concentration (UIC) was measured by collecting spot urine samples. Blood samples were collected to evaluate thyroid function. Thyroid B-ultrasonography was conducted to measure the thyroid volume (Tvol). Results: The median UIC was 168 μg/L (111-263 μg/L). The UIC, free triiodothyronine (FT3), and free thyroxine (FT4) were significantly decreased as the pregnancy progressed (p < 0.001, p for trend <0.001), while Tvol increased (p < 0.001, p for trend <0.001). Thyrotropin (TSH) was significantly different between the 3 trimesters and showed an upward trend (p < 0.001), but the p for trend was not significant (p for trend = 0.88). After stratification by UIC, there were no significant differences in serum TSH, FT4, or FT3 level between UIC groups. Tvol was significantly higher in the UIC ≥500 μg/L group in the first trimester (β: 2.41, 95% CI: 1.09-3.72, p <0.001), as well as in the 250 ≤ UIC < 500 μg/L group (β: 1.65, 95% CI: 0.61-2.70, p < 0.001) and UIC ≥500 μg/L group (β: 3.35, 95% CI: 1.96-4.74, p < 0.001) in the third trimester. Conclusions: No difference was observed in TSH, FT3, or FT4 among the different iodine status groups throughout pregnancy. Tvol increased as the pregnancy progressed, and it was especially higher in the UIC ≥500 μg/L group in the first and third trimesters.

The Effect of Iodine Nutrition during Pregnancy on Their Neonatal Physical Growth and Thyroid Function in Iodine Deficient Area

“…Another study have reported a decreasing trend UIC over the pregnancy [23] . We found maternal TSH levels increased across pregnancy, consistent with the results of a previous study in an iodine su cient area [24] . While another study in an iodine-de cient area [25] reported that no signi cant differences were found regarding the maternal TSH among trimesters.…”

Overview of thyroid gland characteristics in pregnancy using ultrasonography as an assessment tool

“…6 In few studies there was no correlation of thyroid volume in pregnant females with age. 16,17 We also found a positive correlation of age and thyroid volume though it was insignificant.…”

“…BMI had shown a positive correlation with thyroid volume during pregnancy. 6,[16][17][18] Also, Elbrashy et al in his study showed BMI as an independent factor affecting thyroid gland volume. 6 Similarly, in our study, on applying linear regression analysis BMI was found to the sole independent predictor of thyroid volume as seen.…”

Systematic review and meta-analysis on the influence of thyroid dysfunction in early pregnancy on pregnancy outcomes under ultrasound guidance

“…The specific mechanism of placental abruption induced by thyroid dysfunction remains unclear. Postpartum hemorrhage is defined as blood loss with related signs or hypovolemic symptoms that occur within 24 hours of delivery, with a blood loss of 1,000 mL or more at 24 hours postpartum (45). The results in this study showed that thyroid dysfunction could increase the incidence of postpartum hemorrhage.…”