An Investigation into Thyroid Function and Ethnicity in Women with a History of Recurrent Miscarriages

Background:Thyroid disturbances are common in women of reproductive age and it is widely recognised that thyroid dysfunction is associated with both miscarriage and subfertility. Identifying thyroid abnormalities in early pregnancy can predict a spontaneous miscarriage in the current pregnancy;however, the link between subclinical thyroid dysfunction and a history of recurrent miscarriage(RM) is unclear.

Whilst it is accepted that ethnicity affects thyroid function, particularly in pregnant women, it has not been established whether ethnic variation in thyroid function exists in RM women.

Methods:Retrospective thyroid blood results(TPO/TSH/T4) from 229 women with a history of RM(≥2 miscarriages) were collected. Ethnic group(White/Black/Asian) variations in these TFTs were examined by ANOVA(TSH/T4) and logistic regression(TPO). Using the normal ranges TSH[0.44-3.63 µU/ml], TPO[<100 IU/ml] and T4[10-21 pmol/L], participants with thyroid abnormalities were identified(N=27) and compared to a random sample without thyroid abnormalities(N=54). The number of miscarriages and live births(scaled by number of pregnancies) was compared between the two groups by ANOVA. All analyses controlled for age and BMI.

Results:11.8% of RM women had thyroid abnormalities. 10.04% were TPO positive and 4.37% had abnormal TSH(3.93% high/0.44% low). TPO and TSH did not significantly differ between Whites,Blacks and Asians(p=0.577/p=0.226 respectively);however, T4 was significantly mediated by ethnicity(p=0.047); post-hoc t-tests suggested that Asians had lower T4 than Whites(p<0.1). Miscarriages/live births did not differ between patients with and without thyroid abnormalities(p=0.82/p=0.97 respectively).

Conclusions:T4 was significantly mediated by ethnicity with post-hoc tests suggesting Asians had lower T4 than Whites. Further research is needed to assess the potential need for ethnicity-specific thyroid ranges. Abnormal thyroid function did not affect numbers of miscarriages or live births in RM women, suggesting that the absence of routine antenatal thyroid screening is appropriate. However; future research should examine the proportion of women able to have live births after a diagnosis of thyroid abnormalities.