Antioxidants for preventing pre-eclampsia

Pre-eclampsia can occur during pregnancy when women have high blood pressure and protein in their urine. In some cases, it can lead to poor growth for the baby and premature birth. There can also be serious complications for the woman, sometimes affecting the liver, kidneys, brain or blood clotting system. Both mother and baby are at risk of mortality. A possible contributing factor to the development of pre-eclampsia may be the presence of excessive amounts of chemicals called 'free radicals'. Antioxidants, such as vitamin C, vitamin E, selenium and lycopene, can neutralize free radicals. The review covered 10 trials, involving 6533 women, and looked at several antioxidants. Overall the review found no reduction in pre-eclampsia, high blood pressure or preterm birth with the use of antioxidant supplements. When antioxidants were assessed separately, there were insufficient data to be clear about whether there was any benefit or not, except for vitamin C and E. The current evidence does not support the use of antioxidants to reduce the risk of pre-eclampsia or other complications in pregnancy, but there are trials still in progress.

Authors' conclusions: 

Evidence from this review does not support routine antioxidant supplementation during pregnancy to reduce the risk of pre-eclampsia and other serious complications in pregnancy.

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Background: 

Oxidative stress has been proposed as a key factor involved in the development of pre-eclampsia. Supplementing women with antioxidants during pregnancy may help to counteract oxidative stress and thereby prevent or delay the onset of pre-eclampsia.

Objectives: 

To determine the effectiveness and safety of any antioxidant supplementation during pregnancy and the risk of developing pre-eclampsia and its related complications.

Search strategy: 

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (May 2007), the Cochrane Central Register of Controlled Trials (The Cochrane Library 2006, Issue 3), MEDLINE (1950 to October 2007) and Current Contents (1998 to August 2004).

Selection criteria: 

All randomised trials comparing one or more antioxidants with either placebo or no antioxidants during pregnancy for the prevention of pre-eclampsia, and trials comparing one or more antioxidants with another, or with other interventions.

Data collection and analysis: 

Two review authors independently assessed trials for inclusion and trial quality and extracted data.

Main results: 

Ten trials, involving 6533 women, were included in this review, five trials were rated high quality. For the majority of trials, the antioxidant assessed was combined vitamin C and E therapy. There was no significant difference between antioxidant and control groups for the relative risk (RR) of pre-eclampsia (RR 0.73, 95% confidence intervals (CI) 0.51 to 1.06; nine trials, 5446 women) or any other primary outcome: severe pre-eclampsia (RR 1.25, 95% CI 0.89 to 1.76; two trials, 2495 women), preterm birth (before 37 weeks) (RR 1.10, 95% CI 0.99 to 1.22; five trials, 5198 women), small-for-gestational-age infants (RR 0.83, 95% CI 0.62 to 1.11; five trials, 5271 babies) or any baby death (RR 1.12, 95% CI 0.81 to 1.53; four trials, 5144 babies). Women allocated antioxidants were more likely to self-report abdominal pain late in pregnancy (RR 1.61, 95% CI 1.11 to 2.34; one trial, 1745 women), require antihypertensive therapy (RR 1.77, 95% CI 1.22 to 2.57; two trials, 4272 women) and require an antenatal hospital admission for hypertension (RR 1.54, 95% CI 1.00 to 2.39; one trial, 1877 women). However, for the latter two outcomes, this was not clearly reflected in an increase in any other hypertensive complications.

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