Association between indoor residual spraying and pregnancy outcomes: a quasi-experimental study from Uganda

Abstract

Background: Malaria is a risk factor for adverse pregnancy outcomes. Indoor residual spraying with insecticide (IRS) reduces malaria infections, yet the effects of IRS on pregnancy outcomes are not well established. We evaluated the impact of a large-scale IRS campaign on pregnancy outcomes in Eastern Uganda.

Methods: Birth records (n = 59 992) were obtained from routine surveillance data at 25 health facilities from five districts that were part of the IRS campaign and six neighbouring control districts ∼27 months before and ∼24 months after the start of the campaign (January 2013-May 2017). Campaign effects on low birthweight (LBW) and stillbirth incidence were estimated using the matrix completion method (MC-NNM), a machine-learning approach to estimating potential outcomes, and compared with the difference-in-differences (DiD) estimator. Subgroup analyses were conducted by HIV and gravidity.

Results: MC-NNM estimates indicated that the campaign was associated with a 33% reduction in LBW incidence: incidence rate ratio (IRR) = 0.67 [95% confidence interval (CI): 0.49-0.93)]. DiD estimates were similar to MC-NNM [IRR = 0.69 (0.47-1.01)], despite a parallel trends violation during the pre-IRS period. The campaign was not associated with substantial reductions in stillbirth incidence [IRRMC-NNM = 0.94 (0.50-1.77)]. HIV status modified the effects of the IRS campaign on LBW [βIRSxHIV = 0.42 (0.05-0.78)], whereby HIV-negative women appeared to benefit from the campaign [IRR = 0.70 (0.61-0.81)], but not HIV-positive women [IRR = 1.12 (0.59-2.12)].

Conclusions: Our results support the effectiveness of the campaign in Eastern Uganda based on its benefit to LBW prevention, though HIV-positive women may require additional interventions. The IRS campaign was not associated with a substantively lower stillbirth incidence, warranting further research.

Keywords: Plasmodium falciparum; Malaria in pregnancy; adverse pregnancy outcomes; difference-in-differences; indoor residual spraying; low birthweight; matrix completion method; stillbirth.

Figure 1

Location of study districts and health facilities

Figure 2

Flow diagram of the selection of health facilities

Figure 3

Overall, first- and second-year impact of the Uganda IRS Project on low birthweight incidence (A) and stillbirth incidence (B), estimated by the matrix completion method and difference-in-differences models. Average treatment effects on the treated are reported as incidence rate ratios

Figure 4

Month-by-month estimates of the average treatment effect of the treated (ATT) on low birthweight (A) and stillbirth incidence (B). Results are reported as incidence rate ratios estimated using the matrix completion method. The vertical solid lines indicate time points (in months) 0, 12 and 24 after the start of the Uganda IRS campaign. Thick horizontal dashed lines represent the average treatment effect estimated during Years 1 and 2 post-IRS initiation. The horizontal dotted line denotes a reference line when incidence rate ratio = 0

Figure 5

Results of subgroup analyses by HIV. Average treatment effects on the treated were estimated using difference-in-differences models using individual-level data. Results are provided as the overall-, first- and second-year impact of the Uganda IRS Project on low birthweight (A) and stillbirth incidence (B)

Figure 6

Results of subgroup analyses by gravidity. Average treatment effects on the treated group were estimated using difference-in-differences models based on individual-level data. Results are provided as the overall-, first, and second-year impact of the Uganda IRS Project on low birthweight (A) and stillbirth incidence (B)