Women Successfully Treated to Prevent Preterm Labor at Low Risk for Recurrent Episode

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ROCHESTER, Minn. — Mayo Clinic and Medical University of South Carolina researchers have found that the large majority of expectant mothers treated to prevent preterm labor will deliver at or near term.

"We found that if you stopped labor once, only one out of nine women would come back with a repeat episode, which is about a baseline risk for preterm delivery," says Brian Brost, M.D., Mayo Clinic high-risk pregnancy specialist and study co-author. "Most babies will do just fine — they are delivered near term or at term."

While expectant mothers treated with magnesium for preterm labor commonly feel queasy or flushed, serious side effects are rare, according to Dr. Brost, and they usually result from improper dosage or monitoring of the patient following treatment.

The investigators also studied whether the expectant mothers whose preterm labor did recur would be candidates for a steroid treatment in addition to the magnesium. The goal of steroid treatment is to promote accelerated development of the baby's lungs and other body systems. In order for the steroid to be delivered and absorbed into the baby's system, the repeat magnesium treatment to inhibit uterine contractions would need to delay labor for at least 24 to 48 hours. In this study, the researchers found that the magnesium could delay labor long enough for the steroid to work in about half the cases.

This study was conducted retrospectively by analyzing delivery records for consecutive preterm labor patients at Mayo Clinic. In 154 expectant mothers treated for preterm labor who were still undelivered one week later, 87.7 percent (135 women) delivered their babies at greater than 34 weeks. After 34 weeks, standard procedure is to deliver the baby rather than treat the mother again if she went into labor, according to the study's researchers.

In 19 women, or 12.3 percent, preterm labor recurred. Repeat magnesium treatment to inhibit uterine contractions delayed labor for at least 24 to 48 hours in 11 women, offering the possibility for steroid therapy. The other eight women with repeat preterm labor delivered within 24 hours of readmission to the hospital, which did not allow enough time for the physicians to consider giving the steroid treatment.

No measures have been shown to definitively prevent preterm labor, according to Dr. Brost. At the same time, he says, rates of preterm labor have been slowly but steadily rising in the last several decades in the United States.

Newborns are considered to be full-term when delivered about 40 weeks after the first day of their mother's last menstrual period.

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