The study covered in this summary was published on Research Square as a preprint and has not yet been peer reviewed.
Among pregnant women with subclinical hypothyroidism (TSH > 3.74 mIU/L) who did not have thyroid peroxidase antibodies (TPOAb) and who did not receive levothyroxine (LT4) treatment, the prevalence of gestational diabetes and preeclampsia was higher than among pregnant women with normal thyroid (TSH ≤ 3.74 mIU/L) and no TPOAb (reference group) in a new study.
However, among pregnant women with subclinical hypothyroidism without TPOAb who did receive LT4 treatment, the prevalence of gestational diabetes and preeclampsia was similar to that among women in the reference group.
Starting LT4 treatment during the late first trimester to early second trimester was still beneficial with regard to maternal preeclampsia and gestational diabetes (which typically occur later in pregnancy).
The prevalence of iron-deficient anemia was lower in the LT4-treated group than in the reference group.
Why This Matters
There is little evidence on the effect of subclinical hypothyroidism (TSH > 4.0 mIU/L) on pregnancy outcomes, and the results are conflicting.
Few studies have been published regarding pregnant women with subclinical hypothyroidism without TPOAb, possibly because TPOAb is the most frequent cause of this thyroid disorder.
This is the first study involving pregnant women with subclinical hypothyroidism and no TPOAb that shows a beneficial effect of LT4 treatment on maternal pregnancy outcomes of preeclampsia, gestational diabetes, and iron deficiency anemia.
The results provide support for screening pregnant women to determine their serum TSH levels and for providing LT4 treatment to women with subclinical hypothyroidism (TSH from 4.0 – 10.0 mIU/L), regardless of their TPOAb status.
The researchers performed a cross-sectional analysis of data from 1460 pregnant women who had their first antenatal consultation at a single center in Brussels, Belgium, and were screened for thyroid function (TSH, free T4) and autoimmunity (TPOAb) at a median of 13 weeks' gestation from January 2013 to December 2014.
Women were excluded if they had type 1 or type 2 diabetes or thyroid disorders before their pregnancy of if they had twin or assisted pregnancy, TPO positivity, overt hypothyroidism, or treatment with LT4 before screening.
The 71 women who had subclinical hypothyroidism without TPOAb were divided into two groups: 53 women had started LT4 treatment at a median of 13 weeks (aiming to keep TSH levels <2.5 mIU/L), while the other 18 women did not receive this treatment.
The remaining 1389 women with normal thyroid and no TPOAb were the reference group.
The researchers compared rates of preeclampsia, gestational diabetes, iron deficiency anemia, blood loss at birth, emergency cesarean delivery, and preterm birth in the three groups.
The mean age of the women in the three groups was similar (roughly 29 years), as was the prevalence of obesity (roughly 20%).
Preeclampsia was more prevalent among women with subclinical hypothyroidism who did not receive LT4 compared to women in the reference group (16.7% vs 5.0%; P = .017), but the rate was comparable in the LT4-treated subclinical hypothyroidism group compared with the reference group (7.6% vs 5.0%; P = .918).
The prevalence of gestational diabetes was higher among the women with subclinical hypothyroidism who did not receive LT4 compared to women in the reference group (27.8% vs 18.9%; P = .016), but the rate was comparable in the LT4-treated subclinical hypothyroidism group compared with the reference group (22.6% vs 18.9%; P = .676).
The prevalence of iron deficiency anemia was lower among the LT4-treated women than in the reference group (17.0% vs 32.5%; P = .017), and it was similar among the women with subclinical hypothyroidism who did not receive LT4 in comparison with the reference group (50% vs 32.5%; P = .117).
The rate of preterm birth was higher in the LT4-treated group than in the reference group (13.2% vs 5%); the rate was too low (0%) among women with subclinical hypothyroidism who did not receive LT4 to perform a statistical analysis.
Rates of blood loss at birth and emergency cesarean delivery were comparable in the three groups of women.
This was a retrospective analysis.
There was no information about why women with subclinical hypothyroidism were not treated with LT4 (eg, treatment was refused or was not proposed by the physician).
Thyroglobulin antibody (TgAb) levels were not available, so some women may have been misclassified as not having thyroid autoimmunity. (In a study of infertile women in the same geographic area, 5% were found to be positive for TgAb and negative for TPOAb.)
There was no documentation of previous gestational diabetes.
Only women who underwent an oral glucose tolerance test were included in the gestational diabetes outcome, so some women with an increase in fasting glycemia during early pregnancy were excluded, which may have introduced bias.
The study did not receive commercial funding.
The authors have reported no relevant financial relationships.
This is a summary of a preprint research study, "Impact of Thyroid Hormone Treatment on Maternal Pregnancy Outcomes in Women With Subclinical Hypothyroidism Without TPOAb," written by researchers from the Centre Hospitalier Universitaire Saint-Pierre, Brussels, Belgium. Preprints from Research Square are provided to you by Medscape. This study has not yet been peer reviewed. The full text of the study can be found on Research Square.
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Lead image: Chernetskaya/Dreamstime
Cite this: Treat Subclinical Hypothyroidism in Pregnant Women, Study Suggests - Medscape - Jan 10, 2023.