Effects of interventions for helminthic infections in pregnancy [protocol]
Background
Helminthiasis is infestation of the human body with parasitic worms. There are about 20 major helminth infections of humans, and all have some public health significance, but among the commonest of all human infections are the geohelminthiasis (Warren 1993). Global estimates indicate that more than a quarter of the world's population are infected with one or more of the most common of these parasites: the roundworms, Ascaris lumbricoides; the hookworms, Necator americanus and Ancylostoma duodenale; and the whipworm, Trichuris trichura (Chan 1994). Infection with Trichuris trichura and Ascaris lumbricoides typically reaches maximum intensity at 5 to 10 years of age, after which it declines to a lower level that then persists throughout adulthood. A different profile is apparent for hookworm infections, with maximum intensity usually not attained until 20 to 25 years (Stephenson 1987).
Intestinal helminths contribute to anaemia as they feed on blood and cause further haemorrhage by releasing anticoagulant compounds, thereby leading to iron deficiency anaemia. They also contribute by affecting the supply of nutrients necessary for erythropoiesis (Hotez 1983; Torlesse 2000). Although iron deficiency anaemia is multifactorial, hookworm infection is an important contributory cause in endemic areas, especially among the women of reproductive age group. It is the leading cause of pathological blood loss in tropical and subtropical regions (Pawlowski 1991). Globally, an estimated 44 million pregnancies are complicated by maternal hookworm infection alone, posing a serious threat to the health of mothers and fetuses (Bundy 1995). Women in low- and middle-income countries may be pregnant or lactating for as much as half of their reproductive lives (WHO 1994) and estimates indicate that over 50% of the pregnant women have iron deficiency anaemia (ACC/SCN 2000; WHO 1997). Trichuris trichura also causes intestinal blood loss, although much less so than hookworms on a per-worm basis (Bundy 1989). Ascaris lumbricoides interferes with the utilization of vitamin A, which is required for haematopoiesis. All three intestinal helminths may reduce the intake and absorption of iron and other haematopoietic nutrients by causing anorexia, vomiting and diarrhoea (WHO 2003). A study on pregnant women in Liberia found the intensity of hookworm infection, as estimated by faecal egg counts, to be negatively associated with haemoglobin concentration (Jackson 1987).
Anaemia during pregnancy is associated with premature delivery, low birthweight, maternal ill health, and maternal death (Seshadri 1997). Favourable pregnancy outcomes occur 30% to 45% less often in anaemic mothers, and their infants have less then one half of normal iron reserves. Iron deficiency also affects adversely the cognitive performance and development and physical growth of these infants (WHO 2001).
Antihelminthic treatment is regarded as the most effective means of controlling mortality and morbidity due to intestinal helminth infections (WHO 1994). Antihelminthics such as levamisole, mebendazole, albendazole and pyrantel are highly efficacious and have minimal side-effects but data about their use in pregnancy are extremely limited. Few endemic countries have included control of hookworm infections into routine antenatal care. The major obstacles to routine antihelminthic treatment in pregnancy include the concern that the drugs may have teratogenic effects on the fetus, as well as the lack of information to support the health benefits of treatment on pregnancy outcome. In 1994, the World Health Organization convened an informal consultation on hookworm infection and anaemia in girls and women which promoted the use of antihelminthics in pregnancy after the first trimester, but it also recommended evaluation of the long-term safety, particularly in terms of birth outcomes of antihelminthic therapy in pregnancy (WHO 2003). A cross-sectional retrospective study in Sri Lanka in 1995, assessing the effect of mebendazole during pregnancy on birth outcome, found beneficial effects of the therapy on birth outcome, with significantly lower rates of still births, perinatal deaths and very low birthweight babies in the mebendazole group than in the control group. A slightly higher rate of congenital defects was found in women who had taken the drug in the first trimester of pregnancy but the difference was non-significant (de Silva 1999).
The aim of this review is to identify all randomised controlled trials investigating the effects of prophylactic administration of antihelminthics during pregnancy and to evaluate its effects on maternal and pregnancy outcome.
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