Effect of thyroid peroxidase antibody on pregnancy outcome among hypothyroid women

Introduction: Thyroid disorders are among the most common endocrine disorders affecting pregnant women. About 2 to 3% of pregnant women are affected by subclinical hypothyroidism and about 0.3%-0.5% by overt hypothyroidism. Thyroid autoantibodies are found in 5-15% of women in childbearing age and have been associated with adverse pregnancy outcomes. Aim: To compare the pregnancy outcomes in thyroid peroxidase antibody positive and thyroid peroxidase antibody negative hypothyroid women. Materials and Methods: This was a retrospective study done in Dr TMA Pai Hospital, Udupi, Karnataka, India from January 2015 to December 2016. All singleton pregnant women with hypothyroidism were included and multiple pregnancy, preexisting hypertensive or diabetic pregnancies were excluded. Serum Thyroid Stimulating Hormone (TSH) levels were estimated during booking visit for all pregnant women and if >2.5µIU/ml, free T3, T4, and Thyroid Peroxidase Antibody (TPO-Ab) levels were done. Data were retrieved from the hospital records and divided into TPO-Ab negative and TPO-Ab positive groups. The analysis was done using SAS v9.3. Chi-square test and Fisher-Exact test were used for testing equality of proportions. The p-value <0.05 was taken as significant. Results: 2385 antenatal women screened with TSH during the booking visit in study period, 169 (7.08%) were hypothyroid. 100 were TPO-Ab negative and 69 were TPO-Ab positive with 40.8% prevalence of TPO-Ab positivity among the hypothyroid pregnant women. The initial TSH and the average Levothyroxine requirement was 37% (p-value 0.206) and 16% (p-value 0.388) higher in the TPO-Ab positive group than in TPO-Ab negative group. Though the odds for having miscarriage was 2.36 (0.94,5.92), gestational hypertension was 2.71 (0.76, 9.69) and gestational diabetes was 2.88 (0.92,9.03) times higher in the TPO-Ab positive group as compared to TPO-Ab negative group, the p-value for miscarriage was 0.061, gestational hypertension was 0.125 and that for gestational diabetes was 0.062 and hence, statistically not significant. However, there was no difference in the preterm delivery rate in our study. Conclusion: Presence of thyroid peroxidase antibodies may slightly increase the risk of miscarriage, gestational hypertension and gestational diabetes mellitus in pregnancy in the Indian population.