Abstract
ObjectiveIt is unknown if foetal gender influences maternal thyroid function during pregnancy. We therefore investigated the prevalence of thyroid disorders and determined first-trimester TSH reference ranges according to gender.MethodsA cross-sectional study involving 1663 women with an ongoing pregnancy was conducted. Twin and assisted pregnancies and l-thyroxine or antithyroid treatment before pregnancy were exclusion criteria. Serum TSH, free T4 (FT4) and thyroid peroxidase antibodies (TPOAb) were measured at median (interquartile range; IQR) 13 (11–17) weeks of gestation. Subclinical hypothyroidism (SCH) was present when serum TSH levels were >3.74 mIU/L with normal FT4 levels (10.29–18.02 pmol/L), and thyroid autoimmunity (TAI) was present when TPOAb were ≥60 kIU/L.ResultsEight hundred and forty-seven women were pregnant with a female foetus (FF) and 816 with a male foetus (MF). In women without TAI and during the gestational age period between 9 and 13 weeks (with presumed high-serum hCG levels), median (IQR range) serum TSH in the FF group was lower than that in the MF group: 1.13 (0.72–1.74) vs 1.24 (0.71–1.98) mIU/L; P = 0.021. First-trimester gender-specific TSH reference range was 0.03–3.53 mIU/L in the FF group and 0.03–3.89 mIU/L in the MF group. The prevalence of SCH and TAI was comparable between the FF and MF group: 4.4% vs 5.4%; P = 0.345 and 4.9% vs 7.5%; P = 0.079, respectively.ConclusionsWomen pregnant with an MF have slightly but significantly higher TSH levels and a higher upper limit of the first-trimester TSH reference range, compared with pregnancies with a FF. We hypothesise that this difference may be related to higher hCG levels in women pregnant with a FF, although we were unable to measure hCG in this study. Further studies are required to investigate if this difference has any clinical relevance.
Highlights
Thyroid dysfunction in pregnant women is mainly caused by the presence of thyroid autoimmunity (TAI), reflected by increased thyroperoxidase (TPO) and/or thyroglobulin (Tg) antibody levels [1, 2]
We report here a cross-sectional analysis of women with ongoing pregnancies that was nested within the ongoing prospective collection of women’s obstetrical parameters and biological data
After the exclusion of pregnancies resulting from assisted reproduction (n = 32), multiple pregnancies (n = 48) and women treated with l-thyroxine or antithyroid drugs before screening (n = 39), 1663 women were included for comparison of the prevalence of thyroid disorders and baseline/obstetric characteristics between women pregnant with an female foetus (FF) (n = 847) or a male foetus (MF) (n = 816)
Summary
Thyroid dysfunction in pregnant women is mainly caused by the presence of thyroid autoimmunity (TAI), reflected by increased thyroperoxidase (TPO) and/or thyroglobulin (Tg) antibody levels [1, 2]. In a number of studies, the impact of some thyroid parameters on pregnancy outcomes was different according to the foetal gender [7, 8, 9]. Among euthyroid women with TAI, after adjustment for confounders, only women pregnant with a female foetus (FF) had an increased risk of preterm births [9]. Differences in these pregnancy outcomes according to the foetal gender could be explained in part by a sexspecific maternal–placental–foetal interaction such as higher serum hCG levels in women expecting a FF [10, 11]
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