Systematic review to evaluate the potential association of maternal and/or child intestinal parasitic protozoal infection with birth outcomes and linear growth faltering.

Intestinal protozoan infections remain highly prevalent among children and women of reproductive age, particularly across low- and middle-income countries. However, their impact on maternal-child outcomes-including birth weight, prematurity, intrauterine growth restriction (IUGR), and/or childhood stunting remains largely undetermined. Here, we conducted a systematic literature search across six databases for studies published between 1976 and 2024 that examined potential associations between gastrointestinal (GI) protozoan infections, and childbirth and growth outcomes. A total of 99 cross-sectional and longitudinal studies were included. Cross-sectional studies reporting odds ratios (ORs) or adjusted odds ratios (AORs) for stunting, unadjusted and adjusted mean differences (MD) in height-for-age z-score (HAZ), and those reporting regression coefficients for HAZ differences were included in meta-analysis. Meta-analyses of cross-sectional data revealed significant associations between child protozoan infections and stunting, with the strongest evidence for Cryptosporidium spp. (AOR = 2.38, 95 % CI: 1.55 to 3.64). Giardia spp. infections were also associated with higher odds of stunting (AOR = 1.70, 95 % CI: 1.12 to 2.58) and reduced HAZ (MD: -0.42, 95 % CI: -0.53 to -0.30). Narrative synthesis of longitudinal studies supported these associations, providing robust evidence that asymptomatic infections are significantly associated with reduced growth. Five studies examined maternal protozoan infections and birth/stunting outcomes, revealing mixed evidence. Findings underscore the need for improved detection, treatment strategies, and targeted public health interventions, including better access to water, sanitation and hygiene (WASH), to address both symptomatic and asymptomatic protozoan infections. Further research is needed in particular to disentangle the relationship between maternal GI protozoan infections and child health outcomes, and to encompass a broader range of protozoan species to elucidate their impact on childhood stunting.