Insecticide-Treated Nets for the Prevention of Malaria in Pregnancy: A Systematic Review of Randomised Controlled Trials

Abstract

Background

Protection from malaria with insecticide-treated bednets (ITNs) during pregnancy is widely advocated, but evidence of benefit has been inconsistent. We undertook a systematic review of randomised trials.

Methods and Findings

Three cluster-randomised and two individually randomised trials met the inclusion criteria; four from Africa ( n = 6,418) and one from Thailand ( n = 223). In Africa, ITNs compared to no nets increased mean birth weight by 55 g (95% confidence interval [CI] 21–88), reduced low birth weight by 23% (relative risk [RR] 0.77, 95% CI 0.61–0.98), and reduced miscarriages/stillbirths by 33% (RR 0.67, 0.47–0.97) in the first few pregnancies. Placental parasitaemia was reduced by 23% in all gravidae (RR 0.77, 0.66–0.90). The effects were apparent in the cluster-randomised trials and the one individually randomised trial in Africa. The trial in Thailand, which randomised individuals to ITNs or untreated nets, showed reductions in anaemia and fetal loss in all gravidae, but not reductions in clinical malaria or low birth weight.

Conclusions

ITNs used throughout pregnancy or from mid-pregnancy onwards have a beneficial impact on pregnancy outcome in malaria-endemic Africa in the first few pregnancies. The potential impact of ITNs in pregnant women and their newborns in malaria regions outside Africa requires further research.

Abstract

A systematic review of the evidence from trials shows that use of insecticide-treated mosquito nets has a beneficial impact on pregnancy outcome in malaria-endemic Africa in the first few pregnancies.

Editors' Summary

Background.

Malaria is one of the world's most important killer diseases. It is responsible for around a million deaths every year, most of them in Africa and most of them in children. Pregnant women and their unborn babies are also at high risk. Women who have malaria become extremely weak because of anemia, they are more likely to miscarry, and their babies have low birth weights. (Birth weights under 2.5 kilograms are considered to be low; low-birth-weight babies face higher risks of sickness and death than other babies.) It has been estimated that, every year, malaria during pregnancy is responsible for the deaths of about 100,000 to 200,000 babies within their first year of life.

The parasite that causes malaria is carried by certain species of mosquito. In the areas where these mosquitoes are found, taking steps to reduce the chance of being bitten can reduce one's chances of getting infected with malaria. In Africa, these mosquitoes bite mainly in the hours of darkness, so sleeping under a mosquito net helps. During the last 20 years it has been established that mosquito nets impregnated with an insecticide provide much better protection than ordinary nets. Research has shown that children who sleep under these insecticide-treated nets (ITNs) are much less likely to get malaria than other children living in the same area. The correct use of ITNs is now being heavily promoted in many national and international programs.

Why Was This Study Done?

It seems logical that pregnant women should be encouraged to sleep under ITNs, and this is recommended by the World Health Organization and other authorities. However, we cannot be sure that there are benefits, as there is a lack of clear evidence to show whether women who sleep under ITNs actually suffer less from malaria and anemia, and what the implications are for their babies.

What Did the Researchers Do and Find?

They did no new work in the field or in the laboratory. Instead, they conducted what is known as a systematic review. Working to a set of criteria carefully formulated in advance, they searched the medical literature for well-conducted “randomized controlled trials” (RCTs) involving the use of ITNs by pregnant women. RCTs are studies where one group of people receives the “treatment” under investigation and another group does not. It is decided at random who goes into which group. The authors found five trials in Africa, four of which fulfilled the entry criteria for their analysis. In three of the four studies conducted in Africa, whole villages had been “randomized” to determine which pregnant women received ITNs. In another African trial, individual women had been randomized. In total, over 6,000 women were involved in the African trials. One trial had been done outside Africa, in Thailand, where just over 400 individual women had been randomized.

In the research done in Africa, it had been found that women who slept under ITNs had lower numbers of parasites in their blood. Miscarriages were much reduced—by a third in those women who were in their first few pregnancies. The overall proportion of babies who were low birth weight went down by nearly a quarter. In the research done in Thailand, the women using ITNs were less anemic and the miscarriage rate was again lower, although there was no change in the low-birth-weight figures.

What Do These Findings Mean?

The evidence from the three trials done in Africa strongly suggests that it is a good idea for pregnant women to sleep under ITNs. With evidence available from only one trial conducted outside Africa, it is hard to be sure at this stage whether ITNs have the same beneficial effects for pregnant women in other parts of the tropics. More research is needed there.

Additional Information.

The following organizations all have useful information about malaria on their Web sites, and we have provided links to the appropriate pages below. Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040107.

• US Centers for Disease Control and Prevention has information specifically about malaria during pregnancy

• Roll Back Malaria has information specifically about malaria during pregnancy

• Wikipedia—a free online encyclopedia that anyone can edit

• The World Health Organization (WHO)

• The United Nations Children's Fund (UNICEF)

• MedlinePlus brings together authoritative information from the US National Library of Medicine, National Institutes of Health, and other government agencies and health-related organizations

• The Wellcome Trust