Thyroid Disease in Pregnancy Ups Odds of Complications

Marlene Busko

June 06, 2013

Pregnant women with diagnosed thyroid disease are at greater risk for complications such as preeclampsia or preterm birth, the findings of a new retrospective study confirm. The results were published online June 6 in Journal of Clinical Endocrinology & Metabolism.

"Although we know from previous studies that thyroid diseases are associated with pregnancy complications, ours is the largest so far — more than 220,000 pregnancies," lead author Tuija Männistö, MD, from the National Institutes for Health (NIH) Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), in Rockville, Maryland, told Medscape Medical News.

The size of the trial enabled the researchers to examine infrequent conditions, she explained. "We were able to look at rare pregnancy complications…and rare thyroid diseases. We found that hypothyroidism — due to autoimmune disease or to some surgery — and hyperthyroidism were associated with pregnancy complications, hypertensive diseases, and preterm birth and labor induction, and hypothyroidism was also associated with gestational diabetes and cesarean section."

The most novel finding was that both hypothyroidism and hyperthyroidism were associated with much greater likelihood of ICU admission, she added.

Doctors need to appreciate that it is important to carefully monitor expectant mothers who have thyroid disease, she and her colleagues say, as women need appropriate thyroid hormone levels to support a healthy pregnancy.

However, they note that they did not have access to treatment data, so they could not determine whether adequate thyroid treatment might have mitigated these outcomes. "Future research is still needed to distinguish whether women with adequately treated thyroid disease have higher risk of pregnancy complications due to the disease itself or if treatment can truly prevent adverse outcomes," they write.

Eighty Thousand Pregnant Moms a Year Have Thyroid Disease

In the United States, about 4% of pregnant women, or about 80,000 women each year, have thyroid disease, according to Dr. Männistö. However, previous studies that examined pregnancy complications in such women were small or produced inconsistent results.

To look at this more closely, the researchers analyzed data from the Consortium on Safe Labor cohort, a representative sample of women across the United States who gave birth from 2002 to 2008.

They identified 223,512 pregnancies where women gave birth to a single child, including 216,901 women who had no diagnosed thyroid disease. The remaining 3.1% had been diagnosed with:

  • Primary hypothyroidism: 3,183 (1.5%).

  • Hyperthyroidism: 417 (0.2%).

  • Iatrogenic hypothyroidism (due to thyroid surgery or ablation): 178 (0.1%).

  • Goiter, thyroiditis, thyroid nodules, or other disease: 263 (0.1%).

  • Unspecified thyroid disease: 2570 (1.2%).

Compared with women who had no thyroid disease, those with primary hypothyroidism were more likely to have preeclampsia (odds ratio [OR], 1.47), preeclampsia superimposed on hypertension (OR, 2.3), gestational diabetes (OR, 1.57), preterm birth (OR, 1.34), induced labor (OR, 1.15), or a cesarean section (prelabor OR, 1.31; after spontaneous labor OR, 1.38). They were also twice as likely to be admitted to the ICU (OR, 2.08).

Women with hyperthyroidism were more likely to have preeclampsia (OR, 1.78), preeclampsia superimposed on hypertension (OR, 3.64), preterm birth (OR, 1.81), and/or induced labor (OR, 1.40). They were also almost 4 times as likely to be admitted to the ICU (OR, 3.70).

Women with iatrogenic hypothyroidism were more likely to have placental abruption (OR, 2.89), breech presentation (OR, 2.09), and/or a cesarean section after spontaneous labor (OR, 2.05).

Women with goiter, thyroiditis, or nodules had a 2-fold greater risk of having premature rupture of membranes.

Unspecified thyroid disease was associated with similar, though smaller, risks to those borne by women with hypothyroidism.

Physicians need to be aware of these many potential complications from thyroid disease during pregnancy, Dr. Männistö stressed.

The Endocrine Society's clinical practice guidelines for managing thyroid dysfunction during pregnancy and postpartum are available online.

The research was supported by the Intramural Research Program of the NIH Eunice Kennedy Shriver NICHD. The data included in the paper were obtained from the Consortium on Safe Labor, which was supported by the Intramural Research Program of the Eunice Kennedy Shriver NICHD, NIH. The authors have reported no relevant financial relationships.

J Clin Endocrinol Metab. 2013. Abstract

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