SAN FRANCISCO – Pregnancy is one of the few relatively clear reasons to screen and treat for subclinical hypothyroidism, according to Dr. Elizabeth J. Murphy.
There are reasons to consider treating subclinical hypothyroidism in women other than pregnancy, but there’s no clear right or wrong answer in most cases, she said at a conference on women’s health sponsored by the University of California, San Francisco.
Dr. Elizabeth J. Murphy
The Endocrine Society in 2012 recommended against universal thyroid screening of healthy women before pregnancy and said to screen those who are at high risk of thyroid disease, but they rated the evidence for those recommendations as poor (J. Clin. Endocrinol. Metab. 2012;97:2543-65).
For newly pregnant women, the guidelines offered a choice of two options, Dr. Murphy said: Screen all pregnant women by week 9 or at the first prenatal visit (with fair evidence to support this strategy), or screen only high-risk women unless that’s too burdensome, in which case, screen all pregnant women (with poor evidence behind this).
The American College of Obstetricians and Gynecologists (ACOG) Committee on Obstetric Practice issued Opinion No. 381 in 2007 (and reaffirmed it in 2012) saying that routine screening for subclinical hypothyroidism is not currently recommended because there’s no evidence that routinely identifying and treating pregnant women with subclinical hypothyroidism improves outcomes (Obstet. Gynecol. 2007;110:959-60).
"I don’t agree with any of those, and I’m not the only one who doesn’t agree," said Dr. Murphy, chief of the division of endocrinology at San Francisco General Hospital.
A study of serum samples from 25,216 pregnant women and follow-up on their children at ages 7-9 years found lower IQ scores in the offspring of women with undiagnosed hypothyroidism during pregnancy, compared with women whose hypothyroidism was treated prior to pregnancy or euthyroid women in a control group (N. Engl. J. Med. 1999;341:549-55).
A more recent multinational, randomized trial of 21,846 women who were screened at a median of 12 weeks and 3 days of gestation reported that identifying and treating hypothyroidism did not improve the cognitive function of offspring at age 3, compared with a control group whose serum was analyzed after delivery (N. Engl. J. Med. 2012;366:493-501). That study was flawed, however, and "doesn’t provide useful data for prepregnancy screening. It only provides data for screening at 12 weeks," Dr. Murphy said.
The fetal thyroid develops at week 12, and the mother’s thyroid function needs to be in good shape before then, she explained. In addition, the median thyroid-stimulating hormone (TSH) level in the study was low, and half of the women in the study were enrolled not because they had a high TSH level but because they had a low level of free T4, an assay that is "notoriously unreliable in pregnancy," she said. "Many people recommend getting a total T4." It’s unclear whether many of the women who were considered to be hypothyroid truly were. Lastly, 3 years of age might be too young to assess cognitive function in the offspring, she said.
A huge study on the same subject is underway in China with plans to screen 21,500 pregnant women and treat 4,800 for hypothyroidism before pregnancy, she said.
A separate study suggested that both universal thyroid screening in pregnancy and risk-based screening are cost effective, compared with no screening (J. Clin. Endocrinol. Metabol. 2012;97:1536-46).
Guidelines from the American Thyroid Association in 2011 recommended treating pregnant women if the TSH level is greater than 10 mIU/L or if the patient is positive for thyroid peroxidase antibody (Thyroid 2011;21:1081-125). Most clinicians, however, probably would want to treat a woman in early pregnancy whose TSH level is 9 mIU/L, "especially with the IQ data that we have out there," Dr. Murphy said. "Congenital hypothyroidism, remember, is cretinism. It’s really good to have thyroid when your brain’s developing. I would definitely treat a woman with subclinical hypothyroidism who is pregnant."
Dr. Murphy reported having no financial disclosures.
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