VANCOUVER — Subclinical thyroid disease constitutes a novel risk factor for very early preterm delivery, Alex Stagnaro-Green, M.D., said at the annual meeting of the American Thyroid Association.
Based upon new findings from the prospective case-control Camden Study, all women with a history of very early preterm delivery (PTD)—that is, delivery before completing 32 weeks' gestation—should be screened for thyroid disease, according to Dr. Stagnaro-Green, professor of medicine at the New Jersey Medical School, Newark.
The Camden Study is an ongoing investigation looking primarily at the relationship between nutritional factors and pregnancy outcome in a cohort of low-income New Jersey women free of preexisting disease.
Given the growing evidence during the last 15 years demonstrating increased risk of spontaneous abortion in women who have an underactive thyroid or thyroid antibodies, Dr. Stagnaro-Green and his coinvestigators sought to determine whether the incidence of these thyroid abnormalities was also increased in Camden Study participants with PTD.
Of the 953 women in the study who have given birth to date, 124 had PTD, including 28 with very early PTD. These 124 cases were matched to 124 randomly selected controls drawn from the pool of Camden Study participants with term delivery.
Thyroid function testing was performed in all study participants at the first prenatal visit at a mean of 15.5 weeks' gestation. The prevalence of subclinical hypothyroidism as defined by a TSH level of at least 3 mU/L was 14% among women who subsequently had a very early PTD, compared with 6% in women with term delivery or PTD delivery at 32–37 weeks.
Eighteen percent of women who would go on to very early PTD had detectable thyroglobulin antibody levels at the first prenatal visit, a prevalence nearly threefold greater than in all other women. The prevalence of thyroperoxidase antibody was 14% in the very early PTD group and 10% in all others, a difference that did not reach statistical significance.
Dr. Stagnaro-Green said he is aware of a new Texas study that has confirmed the Camden Study findings. These findings are of clinical import because until now, physicians have notably been unsuccessful in predicting or preventing PTD, despite a large research campaign funded by the National Institutes of Health and the March of Dimes.
Indeed, the best predictor found to date of which women will have PTD is a history of PTD. And the only effective treatment identified thus far is weekly intramuscular injections of 17-hydroxy progesterone, which has been shown to modestly reduce recurrences.
PTD imposes an enormous burden on the health care system. It is the number-one cause of perinatal mortality and neurologic disability, with the majority of these outcomes occurring in the subgroup of women who experience very early PTD. PTD accounts for roughly 5,000 perinatal deaths annually. And the incidence of PTD has been on the rise, climbing from 10% in 1987 to 12% in 1998.
“The impact of preterm delivery in the United States and worldwide can't be overstated,” Dr. Stagnaro-Green emphasized.
He added that he personally views the association between thyroid disease and very early PTD as an argument in favor of screening all pregnant women for thyroid disease, a highly controversial proposition that has yet to be incorporated into broad-based practice guidelines.