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

• Published in: Acta clinica belgica (English ed. Online) 2016-05, Vol.71 (S3), p.18
• Main Authors: Maria, Furnica Raluca, Damien, Gruson, Lazarus, John H, Dominique, Maiter, Pierre, Bernard, Chantal, Daumerie
• Format: Article
• Language: English
• Subjects: Health risk assessment; Pregnancy; Thyroid gland
• ISSN: 1784-3286; 2295-3337

Isolated maternal hypothyroxinemia (IH) is defined as a free thyroxine concentration in the lower 5th percentile of the pregnancy-related reference range in conjunction with a normal TSH concentration. The etiology of IH remains unknown. The consequences of IH during early gestation are another source of controversy. Previous studies have shown conflicting results, but there is concern on its potential negative effects on the mother and offspring. The aims of our study were to evaluate the prevalence of first trimester hypothyroxinemia and to assess the consequences of hypothyroxinemia on the maternal and foetal outcomes. The study population of our tertiary centre consisted of 1300 consecutive pregnant women who elected to undergo the first trimester prenatal screen between June 2014 and June 2015. Thyroid function parameters (TSH, free thyroxine - FT4) were assessed during the first trimester (mean gestational age, 11.8 weeks) in 800 pregnant women. The maternal and neonatal outcomes in women identified with IH (n = 55) were compared with those from an euthyroid control group (n = 163). Among the 800 singleton pregnant women, 55 women (6.9%) were identified with severe first trimester hypothyroxinemia. When compared to the euthyroid controls, women with hypothyroxinemia had significantly increased BMI in preconception (25.1 kg/m2 versus 23.3 kg/m2) (p = 0,003) and in the first trimester (25.7 kg/m2 versus 23.6 kg/m2) (p = 0.004). The difference was also significant at the time of delivery (30.5 kg/m2 versus 27.8 kg/m2) (p = 0.001). When comparing the characteristics of deliveries, the proportion of caesarian section was significantly higher in the IH group (32.7% versus 17.8%; p = 0.026). At term, foetal breech presentation was significantly higher than in the euthyroid controls (p = 0.006). A significantly increase in macrosomia was also noted (p = 0.026). The prevalence of hypothyroxinemia in early pregnancy was of 6.9%. Early pregnancy hypothyroxinemia is associated with an increased maternal BMI and is related with a risk of breech presentation at birth, a significant increase in the occurrence of macrosomia and caesarian sections. Screening should consider overweight as a potential risk factor for thyroid dysfunction in pregnant women and specifically hypothyroxinaemia.