Previous hyperthyroidism confers residual risk for prenatal, perinatal complications
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Pregnant women with hyperthyroidism or a history of hyperthyroid disease are at increased risk for gestational hypertension, preterm birth, an infant born small for gestational age and neonatal ICU admission, study data show.
“Hyperthyroid mothers are assumed to be at high risk of developing pregnancy and/or perinatal complications due to active disease, and this was confirmed in the present study,” Suvi Turunen, MD, of the department of obstetrics and gynecology at the University of Oulu and Oulu University Hospital, Finland, and colleagues wrote. “In contrast, the majority of our study population (73%) did not use antithyroid drugs during pregnancy, and 23% used levothyroxine; both of these results suggest that these mothers had histories of hyperthyroidism rather than active disease that required treatment during pregnancy. Interestingly, we observed increased odds of adverse outcomes among these mothers as well, suggesting that a previous diagnosis of hyperthyroidism itself may pose a residual risk of developing pregnancy and/or perinatal complications.”
Turunen and colleagues analyzed data from 357,293 women with 571,785 singleton pregnancies in Finland between 2004 and 2013, using data from the Medical Birth Register. Mothers with hyperthyroidism were identified via registry data; data on antithyroid medication use before and/or during pregnancy were collected via prescription registry. Researchers used logistic regression analysis to assess ORs for adverse outcomes among mother with hyperthyroidism vs. mothers without thyroid disease.
Within the cohort, 2,144 women (0.37%) had diagnoses of hyperthyroidism, of whom 580 (27%) had used antithyroid medications before and/or during pregnancy.
Researchers found that maternal hyperthyroidism was associated with a higher risk for gestational hypertensive disorders among women who used antithyroid medications (OR = 1.67; 95% CI, 1.18-2.36), but not for women without a history of antithyroid medication use.
Maternal hyperthyroidism was associated with preterm birth (OR = 1.34; 95% CI, 1.09-1.64), early preterm birth (OR = 1.87; 95% CI, 1.39-2.53), newborns born small for gestational age (OR = 1.3; 95% CI, 1.04-1.63) and neonatal ICU admission (OR = 1.65; 95% CI, 1.46-1.86).
Maternal hyperthyroidism was also associated with a higher risk for respiratory treatment for the newborn among women who used antithyroid medications (OR = 1.95; 95% CI, 1.07-3.56), but not for women who did not use thyroid medication.
Maternal hyperthyroidism was not associated with gestational diabetes, instrumental delivery or placenta previa. The overall prevalence of stillbirth and early neonatal death was low and did not differ between groups.
The researchers wrote that the findings support the hypotheses that thyroid disorders can be considered expressions of autoimmunity in general and that adverse pregnancy and perinatal outcomes may be associated with other underlying autoimmune diseases.
Perspective
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Caroline Nguyen, MD
The results of this large national study by Turunen and colleagues reaffirm findings of prior studies: Hyperthyroidism in pregnancy is associated with increased risks for several maternal and fetal complications. Interestingly, patients with a history of hyperthyroidism also had increased risk for complications compared with those with no history of thyroid disease, suggesting that close monitoring of women with hyperthyroidism as well as women with a history of hyperthyroidism and their fetuses is essential throughout pregnancy. Furthermore, the risks for complications were higher among women who were taking antithyroid drugs — active disease — compared with those who were not taking antithyroid drugs. This finding emphasizes the importance of preconception counseling for all women of childbearing age with hyperthyroidism at the time of diagnosis.
A woman's plans for pregnancy and her timeline should be taken into consideration when discussing hyperthyroid treatment options. Equally important is contraception and avoiding pregnancy until hyperthyroidism is adequately controlled. The physician’s goal should be to effectively treat hyperthyroidism prior to pregnancy to decrease the risks for complications and the need for antithyroid medication during pregnancy.
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