In this study, we found that 21% of mothers had peripheral (maternal) and/or placental parasitaemia at parturition. Previous studies from Nigeria reported parasitaemia rates among pregnant women or at parturition ranging from 24.8–80% [15
]. Studies from other malaria endemic parts of Africa have also reported large variations in the occurrence of malaria parasitaemia among the pregnant women. For instance, in Cameroon; Walker-Abbey et al. [26
] reported a prevalence of 82.4% while Tako et al. [27
] reported a total malaria positivity rate of 21.5%. The wide ranges in reported prevalence of malaria may be due to multiple factors. One factor is the method of diagnosis. The studies that reported very high rates, that is, >70%, were those that involved the use of PCR for parasite detection. In one of such studies with 82% prevalence, only 27.5% were detectable by microscopy while parasitaemia was sub-microscopic in over 50% [26
]. Other factors that may explain this variation include intensity of transmission, study population characteristics (age, parity, HIV status), use of preventive measures (e.g., IPT, ITNs), and study design. Many studies had small sample sizes and were restricted to just a single site. This was a multicentre study across the major geographic and ecological zones of Nigeria and would therefore be expected to be more representative of the true situation of malaria at parturition in the country. To the best of the authors' knowledge this is the largest study of a multicentre dimension to be conducted on peripartum malaria in Nigeria.
In this study, parasitaemia at the time of delivery was found to be associated with low parity and maternal age. Several other studies have reported similar associations [27
]. A multivariate analysis however revealed that only the age of the women less than 20 years was significantly associated with parasitaemia in the women. This finding was also described by Tako et al. [27
] and Saute et al. [29
]. In both of these studies multivariate analysis found that younger maternal age, (teens to less than 25 years), was significantly associated with placental parasitaemia after adjusting for confounding variables like parity. The authors observed that younger but not older first time mothers were more likely to have placental malaria [27
] or peripheral blood malaria [29
]. In the light of this finding Tako et al. [27
] suggested that pregnancy-associated immunity and naturally acquired immunity may differ among women in Yaoundé, Cameroon. The hypothesis was that the development of pregnancy associated immunity, for example, production of antibodies that inhibit adherence of placental parasites to chondroitin sulphate A, may be very important in women <25 years of age who have lower levels of acquired immunity. While older women living in such endemic areas may have obtained adequate immunity following repeated exposures to eliminate any infecting malaria parasite and are thus less dependent on anticytoadherent antibodies [27
]. Whereas this hypothesis is plausible, it is not certain whether it will also explain the fact that the observed relationship is not limited to only placental parasitaemia since the same was true for parasitaemia in the maternal peripheral blood.
Parasitaemia in the mothers was found to be significantly associated with lower maternal hematocrit. This finding is not unexpected as the association of malaria in pregnancy and low hematocrit has been recognized and reported by previous workers [14
]. The drop in hematocrit occurs as a result of the fact that parasitized and unparasitized erythrocytes are destroyed by the spleen during malaria infection. It is however known that using drugs that are normally effective against malaria within a locality significantly reduces the occurrence of this anaemia [31
The main effect of maternal parasitaemia on the babies is the reduction in the birth weight. This is consistent with the observations from other malaria endemic countries [32
]. Considering that a needle aspiration technique was applied for placenta parasite detection, it was not possible, in this study, to distinguish between acute and chronic stages of the placental infection. The impact of malaria during pregnancy on LBW in sub-Sahara Africa has been extensively reviewed [36
]. It has been estimated that in areas where malaria is endemic, about 19% of LBW infants are due to malaria and 6% of infant deaths are due to LBW caused by malaria. These estimates imply that around 100 000 infant deaths each year could be due to LBW caused by malaria during pregnancy in areas of malaria endemicity in Africa [37
The observed impact of malaria on the mother and their newborns add justification for promoting use of malaria preventive measure in pregnancy. The tools for achieving effective malaria control are now available; these include use of ITNs, IPT, and effective treatment. The use of these tools is also being facilitated with the recent production of a number of treatment guidelines and policy documents [17
]. In the present study the level of use of malaria preventive measures was generally low. It is essential that all stakeholders combine efforts to ensure successful implementation in the deployment of these various tools in order to achieve a reduction in the burden of malaria in pregnancy in Nigeria.