Does foetal gender influence maternal thyroid parameters in pregnancy?

Abstract

Objective It 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. Methods A 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. Results Eight 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. Conclusions Women 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.

Impact of thyroid hormone treatment on maternal pregnancy outcomes in women with subclinical hypothyroidism without TPOAb

“…In one study in euthyroid women, TPOAb positivity was strongly associated with PTB, but only in case of pregnancies with female foetuses [33]. Furthermore, in a recent study by Sitoris et al, it was observed that serum TSH levels in women pregnant with a female foetus were higher compared with those in women pregnant with a male one, probably due to differences in hCG levels and/or other placental factors [34].…”

Gestation-suppressed serum TSH levels during early pregnancy are not associated with altered maternal and neonatal outcomes

“…Another parameter for which in more recent studies an adjustment is made is the fetal gender. Previous studies have shown that maternal TSH levels were lower in women pregnant with a female fetus, probably due to higher hCG levels and/or other placental substances like the vascular endothelial growth factor with an impact on thyroid vascularisation ( 24 ). Moreover, in one study, thyroid disorders were associated with PTB only in case of pregnancies with a female fetus ( 25 ).…”

Longitudinal trajectories of maternal TSH in healthy pregnant women in Catalonia

“…Recent data have also shown that the fetal gender might lead to changes in thyroid function ( 23 ). In our study, no differences were observed in TSH values between pregnant women who gave birth to MF and those who gave birth to FF in each trimester.…”