Malarial infection and birthweight in urban Zanzibar, Tanzania.

In urban Zanzibar, Tanzania, 389 women with full-term pregnancies were studied to see what effect their infection with malaria (at delivery) had on the birthweight (BW) of their infants. The overall prevalence of low birthweight (LBW) (i.e. < 2500 g) was 3.9% (15 out of 389). Overall, 21.3% (82/384) of the women only had peripheral parasitaemias at delivery, 17.6% (58/329) only had active placental infections and 47.9% (157/328) had both. The youngest women (< 20 years), the primiparae and those with Plasmodium infection gave birth to neonates with relatively low mean BW. The lowest mean BW (2967 g) was found among the offspring of women with active placental infection (N = 58). The women with past/chronic infection (N = 73) or no infection (N = 201) generally produced heavier infants, with mean BW of 3242 and 3338 g, respectively. The women with active placental infection were also far more likely to have babies of LBW (15.5%) than those with past/chronic infection (1.4%) or no infection (1.5%). Multivariate analysis indicated that the highest relative risk of LBW (10.1, with a 95% confidence interval of 2.9-35.4) was associated with active placental infection, with no significant difference between primiparae and multiparae. In the study population, therefore, with its low prevalence of LBW, malaria infection increased the risk of LBW in full-term neonates by about 10-fold, with a population-attributable proportion of 55.4%.