The drug most commonly used to delay pre-term labor in pregnant women has more - and more serious - side effects than alternatives without being any more effective, Stanford University researchers reported yesterday. The drug might cause harm to infants, they concluded.
Although it is generally not possible to stop labor completely, physicians try to delay it for at least 48 hours to allow transfer of the mother to a specialized hospital and to maximize the effectiveness of steroids used to help the lungs of the fetus mature.
The drug most commonly used is magnesium sulfate, but nifedipine and some others are occasionally used.
"There is no free lunch with any of these drugs," collectively called tocolytic agents, said Dr. Deirdre Lyell of the Stanford School of Medicine. "But magnesium sulfate has some particularly unpleasant side effects, including vomiting, lethargy and blurry vision. The alternative, nifedipine, often leaves women feeling better."
Despite obstetric advances, pre-term birth - before 37 weeks of gestation - remains a major problem, affecting 12.3 percent of births in the United States for reasons that are largely unknown. It is the cause of 30 percent of infant deaths and a broad variety of developmental problems in those who survive.
Lyell, Dr. Yasser El-Sayed of Stanford and their colleagues studied 192 women in pre-term labor. Half were randomly assigned to receive infusions of magnesium sulfate, and half received oral nifedipine.
The team reported in the journal Obstetrics & Gynecology that, while magnesium sulfate quieted contractions more effectively than nifedipine, there was no difference in the treatments' ability to delay delivery, in the gestational age of the newborn or in the birth weight of the infants.
However, two-thirds of the women who received magnesium sulfate experienced mild to severe side effects, including shortness of breath and fluid buildup in the lungs. Only one-third of the women receiving nifedipine experienced side effects, such as headaches.
Infants born to the mothers who received magnesium sulfate, moreover, were more likely to be admitted to the neonatal intensive care unit and to stay there longer - a median of 8.8 days compared with 4.2 days for the nifedipine babies.
Dr. Victoria Camerini, a Los Angeles neonatologist who was not involved in the study, said that magnesium can cause respiratory depression and bowel dysfunction in infants and that the mother's body can transport it across the placenta.
"If an obstetrician asked me which drug I would prefer," she said, "I would say nifedipine."
The researchers said magnesium sulfate is still an appropriate treatment for pre-term labor, and many physicians continue to use it at the two hospitals where the study was done.
Thomas H. Maugh II writes for the Los Angeles Times.