The study, published in The New England Journal of Medicine, included 1,877 healthy pregnant women who took vitamins C and E or empty pills (placebo) during their pregnancy.
The vitamin group showed no advantages in the risk of preeclampsia, death, or serious outcomes in the infants, or low-birth-weight babies. The results "do not support routine supplementation" with vitamins C and E to reduce those risks, write the researchers. They included Alice Rumbold, PhD, of the obstetrics and gynecology department of Australia's University of Adelaide.
Preeclampsia only occurs during pregnancy. It affects 5% of 8% of all pregnancies.
Preeclampsia occurs when a pregnant woman develops high blood pressure along with protein in her urine. Swelling, sudden weight gain, and headaches may also occur. This condition is dangerous for mother and baby alike. It can lead to low-birth-weight babies, preterm birth, and problems with the mother's kidneys, liver, and ability to avoid uncontrolled bleeding. Eclampsia, a life-threatening situation for mother and baby, is preeclampsia with seizures.
Any pregnant woman can get preeclampsia, but a woman is at increased risk of developing the condition if:
- This is her first pregnancy.
- Her mother or sister had preeclampsia or eclampsia during pregnancy.
- She is carrying twins.
- She is black.
- She is younger than 20 or older than 40 at the time of pregnancy.
- She already has high blood pressure, kidney disease, or diabetes.
- Her body mass index (BMI)is greater than 30 before pregnancy.
The women in Rumbold's study hadn't given birth before. Each was only carrying one baby. The women had similar backgrounds. Their dietary intake of vitamins C and E was also similar, according to surveys the women completed at the study's start.
Rumbold's team randomly assigned roughly half of the women to the vitamin group. The researchers gave those women daily supplements totaling 1,000 milligrams of vitamin C and 400 international units (IU) of vitamin E (as d-alpha-tocopherol succinate).
No one knew who got the vitamins and who got the placebo. Either way, the women were told to swallow two of the pills in the morning and two in the evening.
Other antioxidant supplements were off limits during the study. But the women were allowed to take daily multivitamins containing up to 200 milligrams of vitamin C or 50 international units of vitamin E.
Most women didn't develop preeclampsiaor other problems covered in the study.
Preeclampsia developed in 6% of the women in the vitamin group and 5% of the placebo group. Infants died or had serious complications in 9.5% of the vitamin group, compared with about 12% of the placebo group. Babies were at low weight for their gestational age for about 9% of the vitamin group and nearly 10% of the placebo group.
Those differences were small enough that they could have been due to chance, the study shows.
Fewer babies in the vitamin group had respiratory distress syndrome or needed surfactant, which helps in breathing. That finding didn't appear to be due to chance.
After giving birth, women in the vitamin group had an increased risk of being hospitalized for high blood pressureor being prescribed drugs to tame high blood pressure. However, those findings may have been due to chance, the researchers note.
Diet May Have Mattered
Before the study, most participants got more vitamin C and vitamin E from their diets than the recommended daily amount of those vitamins.
"Thus, the results cannot be generalized to women with low dietary intakes of antioxidants," write Rumbold and colleagues.
An earlier study showed that supplementation with vitamins C and E "was beneficial for women at high risk of preeclampsia," Rumbold's team writes. But Rumbold's study didn't focus on high-risk women.
Other studies on the topic are under way in the U.S. and overseas, the researchers note.
Some current studies on antioxidant supplements and preeclampsia are being conducted in developing nations.
In those countries, "the intake of antioxidants may be less and the benefit of supplementation may be greater than in developed nations," write editorialists Arun Jeyabalan, MD, and Steve Caritis, MD. Jeyabalan and Caritis work in Pittsburgh at the maternal-fetal medicine division of Magee-Womens Hospital and the University of Pittsburgh.
Until more data are available, "supplemental antioxidant therapy for the prevention of preeclampsia should be limited to women enrolled in randomized trials and should not be prescribed as part of routine practice," the editorial states.