First trimester isolated maternal hypothyroxinemia: adverse maternal metabolic profile and impact on the obstetrical outcome

Abstract

Background

Isolated maternal hypothyroxinemia (IH) is defined as low maternal FT4 (<5^th percentile) and normal TSH. There is concern on its potential negative effects on the mother and offspring.

Objective

We aimed to evaluate the prevalence of IH and to assess the consequences of hypothyroxinemia on the maternal and foetal outcomes.

Subjects and methods

From a total of 1300 consecutive pregnant women recruited during the prenatal screen (mean gestational age, 11.8 weeks), thyroid function parameters were assessed in 879 women. After exclusion of women with T4 supplements, with twin pregnancies and with diabetes, data from 783 women were included. Maternal and neonatal outcomes in 55 selected women with IH and negative thyroid auto antibodies, without thyroid disorders or pregnancy achieved through assisted reproductive techniques were compared with a selected euthyroid control group (N=165).

Results

Among the 783 non - diabetic singleton pregnant women, 68 women (8.7%) were identified with IH. When compared to the selected euthyroid controls, selected women with hypothyroxinemia had significantly increased BMI in preconception (p=0.003), in the first trimester (p=0.004) and at the time of delivery (p=0.001). At term, foetal breech presentation and caesarian section rate were significantly higher (p=0.006 and p=0.026, respectively) than in the euthyroid controls. A significantly increase in macrosomia was also noted (p=0.026).

Conclusion

The prevalence of hypothyroxinemia in early pregnancy was of 8.7%. IH is associated with an increased maternal BMI and is related with a risk of breech presentation, a significant increase in macrosomia and caesarian sections. Screening should consider overweight as risk factor for hypothyroxinaemia.

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