European Thyroid Journal (Jan 2023)
Does foetal gender influence maternal thyroid parameters in pregnancy?
Abstract
Objective: It is unknown if foetal gender influences maternal thyroid func tion during pregnancy. We therefore investigated the prevalence of thyroid disorders and determined first-trimester TSH reference ranges according to gen der. Methods: A cross-sectional study involving 1663 women with an ongoing p regnancy was conducted. Twin and assisted pregnancies and l-thyroxine or antithyroid treatment before pregnancy were exclusion criteria. Serum TSH, free T4 (F T4) and thyroid peroxidase antibodies (TPOAb) were measured at median (interqua rtile range; IQR) 13 (11–17) weeks of gestation. Subclinical hypothyroidism (SCH) wa s 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. Results: Eight hundred and forty-seven women were pregnant with a femal e foetus (FF) and 816 with a male foetus (MF). In women without TAI and durin g the gestational age period between 9 and 13 weeks (with presumed high-serum hCG lev els), 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 i n 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. Conclusions: Women pregnant with an MF have slightly but significantly highe r TSH levels and a higher upper limit of the first-trimester TSH reference ra nge, compared with pregnancies with a FF. We hypothesise that this difference may b e 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 diffe rence has any clinical relevance.
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