Background Investigating whether the multiplicity of Plasmodium falciparum infection (MOI) is related to pregnancy outcomes, is of interest in sub-Saharan area where malaria is highly endemic. The present study aimed to characterize the genetic diversity of P. falciparum in women at delivery from Southern Brazzaville, and investigate whether the MOI is associated with maternal anaemia, preterm delivery, or low birth weight. Methods This was a cross sectional study carried out with samples collected between March 2014 and April 2015 from 371 women recruited at delivery at a Health Centre in southern Brazzaville, Republic of Congo. Matched peripheral, placental, and cord blood collected from each of the women at delivery were used for the detection of P. falciparum microscopic and submicroscopic parasitaemia, and parasite DNA genotyping by nested PCR. Results From 371 recruited women, 27 were positive to microscopic malaria parasitaemia while 223 women harboured submicroscopic parasitaemia. All msp-1 block 2 family allelic types (K1, MAD20 and RO33) were observed in all the three compartments of blood, with K1 being most abundant. K1 (with 12, 10, and 08 alleles in the peripheral, placental, and cord blood respectively) and MAD20 (with 10, 09, and 06 alleles in the respective blood compartments) were more diverse compared to RO33 (with 06, 06, and 05 alleles in the respective blood compartments). From the 250 women with microscopic and/or submicroscopic parasitaemia, 38.5%, 30.5%, and 18.4% of peripheral, placental and cord blood sample, respectively, harboured more than one parasite clone, and polyclonal infection was more prevalent in the peripheral blood of women with microscopic parasitaemia (54.5%) compared to those with submicroscopic parasitaemia (36.7%) (p = 0.02). The mean multiplicity of genotypes per microscopic and submicroscopic infection in peripheral blood was higher in anemic women (2.00 ± 0.23 and 1.66 ± 0.11, respectively) than in non-anaemic women (1.36 ± 0.15 and 1.45 ± 0.06, respectively) (p = 0.03 and 0.06). In logistic regression, women infected with four or more clones of the parasite were 9.4 times more likely to be anaemic than women harbouring one clone. This association, however, was only observed with the peripheral blood infection. No significant association was found between the MOI and low birth weight or preterm delivery. Conclusions These results indicate that the genetic diversity of P. falciparum is high in pregnant women from southern Brazzaville in the Republic of Congo, and the multiplicity of the infection might represent a risk for maternal anaemia.

Suphodoxine-Pyrimethamine (SP) acts by inhibiting P. falciparum replication, therefore, long term use of SP in malarial endemic sittings as intermittent preventive treatment (IPT) during pregnancy might lead to increased risk of submicroscopic parasitaemia. The present study aimed to determine the prevalence of submicroscopic P. falciparum infection in women at delivery from southern Brazzaville, where IPT-SP has been implemented since 2004, and investigate the relationship between the submicroscopic parasitaemia and pregnancy outcomes. This descriptive cross-sectional study was carried out from March 2014 to April 2015 with 281 women randomly recruited at delivery at a Health Centre in southern Brazzaville, Republic of Congo. Matched peripheral, placental, and cord blood collected from each women with malaria negative thick smears, were used for the diagnostic of P.falciparum submicroscopic infection by nested-polymerase chain reaction (nPCR) targeting the multi-copy 18 S ribosomal ARN gene. The prevalence of P.falciparum submicroscopic infection was 31.7%, 36.37%, and 12.9%, when using the peripheral, placental, and cord blood respectively. The submicroscopic P. falciparum was slightly associated with increased risk of maternal anaemia (adjusted odds ratio [OR] 1.33, 95% CI 0.82-2.17). No significant association was found between the submicroscopic parasitaemia and low birth weight, or preterm delivery. The data suggest that the prevalence of submicroscopic P. falciparum infection is high in women at delivery in Brazzaville; and might increase the risk for maternal anaemia. The infection had no impact on the prevalence of low birth weight and preterm delivery in this study sitting.