Minimal Impact by Antenatal Subpatent Plasmodium falciparum Infections on Delivery Outcomes in Malawian Women: A Cohort Study

Abstract

Antenatal malaria screening with a rapid diagnostic test (RDT) and treatment only of women with positive RDT findings may potentially prevent low birth weight resulting from malaria. The consequences of subpatent antenatal infections below the detection limit of RDTs are incompletely understood. In Malawi, pregnant women of any gravidity status were tested at each antenatal visit for Plasmodium falciparum, using an RDT and polymerase chain reaction analysis, and were followed until delivery. Associations between antenatal infections and delivery outcomes were assessed with Poisson regression or analysis of variance. Compared with women with no detected antenatal P. falciparum infection, women with positive RDT findings delivered babies with a lower mean birth weight (2960 vs 2867 g; mean difference, -93 g [95% confidence interval {CI}, -27 to -159]; P = .006); this was not observed among women with only subpatent infections (mean birth weight, 3013 g; mean difference, 54 [95% CI, -33-140]; P = .2268). These differences were apparent early in pregnancy, during the second trimester: compared with uninfected women, women with positive RDT findings delivered babies with a lower mean birth weight (mean difference, -94 g [95% CI, -31 to -156]; P = .003), but women with subpatent infections did not (mean difference, 36 g [95% CI, -49-122]; P = .409). Subpatent antenatal P. falciparum infections were not associated with adverse delivery outcomes. The association of patent infections at enrollment with low birth weight suggests the importance of preventing P. falciparum infection early in pregnancy.

Keywords: Malaria in pregnancy; low birth weight; malaria parasite detection; rapid diagnostic test.

© The Author 2017. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.

Figures

Figure 1.

Prevalence of antenatal Plasmodium falciparum infections. A, Prevalence of uninfected women (white), women with positive results of rapid diagnostic tests (RDTs; black), and women with subpatent infections (gray) at enrollment, scheduled visits 1 (1st), 2 (2nd), and 3 (3rd), and unscheduled visits 1 (U1), 2 (U2), and 3 (U3). Widths of columns are proportional to the number of women tested. B, Distributions of the numbers of antenatal RDT-positive and subpatent infections.

Figure 2.

Impacts of rapid diagnostic test (RDT)–positive and subpatent infections at enrollment and cumulatively during pregnancy on continuous birth outcomes. Data are mean differences (95% confidence intervals) from values for uninfected women and were computed from pair-wise comparisons of means, using analysis of variance. Details for the number of women contributing and the mean values are reported in Supplementary Tables 1 and 3.

Figure 3.

Impacts of rapid diagnostic test (RDT)–positive and subpatent infections at enrollment and cumulatively during pregnancy on dichotomous birth outcomes. Risk ratios (RRs) were computed with Poisson regression and adjusted for gravidity in the aggregated analysis. Subpatent infections were defined as infections in women with negative results of RDT and positive results of polymerase chain reaction. Maternal anemia was defined as a hemoglobin concentration of