Kristie McNealy, MD

Last year, a study came out which compared to common preterm labor drugs – magnesium sulfate (mag) and nifedipine. The study showed that while mag was better at stop uterine contractions in women in preterm labor, it was not significantly more effective at preventing delivery within 48 hours or preventing recurrent preterm labor than nifedipine. In addition, the study showed that there were significantly more mild and severe adverse reactions in moms given magnesium sulfate, and their preemie babies spent significantly longer in the neonatal intensive care unit.

As a result of this study, many practitioners turned to nifedipine as their first line treatment of preterm labor. In fact, during my last pregnancy, I was overjoyed when my midwife told me they rarely used mag for preterm labor any more. You see, mag has some nasty side effects, including vomiting and double vision, and some serious potential consequences like cardiac or respiratory failure if blood concentrations get too high. A mom on mag can’t eat solid foods or get out of bed. In some hospitals, they can’t even have visitors. While women in preterm labor are commonly given 48 hours of mag, some women end up having to stay on it for weeks. I’d have to say that the 48 hours I spent on a mag during my second pregnancy were easily the most physically miserable days of my life.

With my third child, I was treated with nifedipine after I went into preterm labor at 32 weeks. Although there were some side effects, like dizziness and a racing heart when I stood up, I felt pretty good, and I was able to take the medicine at home.

However, two new studies out of Australia and the University of Alabama now show that using magnesium sulfate may cut the rate of moderate to severe cerebral palsy at the age of two by almost half. Now, researchers and leading obstetricians are encouraging physicians to use magnesium sulfate once again. It’s a confusing issue, because the women in the study who were not treated with mag got a placebo infusion instead. So, this was not a head to head comparison of mag and nifedipine, but rather mag and regular IV fluids.

In my mind, this study really needs to be followed up by a study comparing the outcomes at 2 years of age in babies whose moms were treated with nifedipine versus magnesium. Anyone know of a study like this out there?