Hookworm-related anaemia among pregnant women: a systematic review

Abstract

Background and objectives: Hookworm infection is among the major causes of anaemia in poor communities, but its importance in causing maternal anaemia is poorly understood, and this has hampered effective lobbying for the inclusion of anthelmintic treatment in maternal health packages. We sought to review existing evidence on the role of hookworm as a risk factor for anaemia among pregnant women. We also estimate the number of hookworm infections in pregnant women in sub-Saharan Africa (SSA).

Methods: Structured searches using MEDLINE and EMBASE as well as manual searches of reference lists were conducted, and unpublished data were obtained by contacting authors. Papers were independently reviewed by two authors, and relevant data were extracted. We compared haemoglobin concentration (Hb) according to intensity of hookworm infection and calculated standardised mean differences and 95% confidence intervals. To estimate the number of pregnant women, we used population surfaces and a spatial model of hookworm prevalence.

Findings: One hundred and five reports were screened and 19 were eligible for inclusion: 13 cross-sectional studies, 2 randomised controlled trials, 2 non-randomised treatment trials and 2 observational studies. Comparing uninfected women and women lightly (1-1,999 eggs/gram [epg]) infected with hookworm, the standardised mean difference (SMD) was -0.24 (95% CI: -0.36 to -0.13). The SMD between women heavily (4000+ epg) infected and those lightly infected was -0.57 (95% CI: -0.87 to -0.26). All identified intervention studies showed a benefit of deworming for maternal or child health, but since a variety of outcomes measures were employed, quantitative evaluation was not possible. We estimate that 37.7 million women of reproductive age in SSA are infected with hookworm in 2005 and that approximately 6.9 million pregnant women are infected.

Conclusions: Evidence indicates that increasing hookworm infection intensity is associated with lower haemoglobin levels in pregnant women in poor countries. There are insufficient data to quantify the benefits of deworming, and further studies are warranted. Given that between a quarter and a third of pregnant women in SSA are infected with hookworm and at risk of preventable hookworm-related anaemia, efforts should be made to increase the coverage of anthelmintic treatment among pregnant women.

Figure 1. Forest plot of the difference in haemoglobin (Hb) concentration among pregnant women uninfected with hookworm and women harbouring a light (1–1,999 eggs/gram) hookworm infection.

Standardised mean difference less than zero indicate lower Hb levels in lightly infected women compared to uninfected women. The diamond represents the overall pooled estimates of the effect of light hookworm infection on Hb.

Figure 2. Forest plot of the difference in haemoglobin (Hb) concentration among pregnant women women harbouring a light (1–1,999 eggs/gram) hookworm infection and women harbouring a heavy (4,000+ eggs/gram) infection.

Standardised mean difference less than zero indicate lower Hb levels in heavily infected women compared to lightly infected women. The diamond represents the overall pooled estimates of the effect of heavy hookworm infection on Hb.