This study describes the clinical and epidemiological characteristics of pregnant women with malaria in Venezuela. Infection by P. vivax was the most frequent in this study in agreement with the malaria species distribution in the country [26] as well as with other studies in pregnant women in Venezuela [9, 27, 28] and Latin American [17, 29, 30]. Mixed infections were also frequent, similar to reported by Morao et al. [31]. As reported previously [10, 29, 31, 32], most of the women were young, with several of them being adolescents, reflecting the fertility rate reported for Venezuela, the highest in Latin America, with 85 births per 1,000 adolescents aged between 15-19 years old in 2018 [33]. Similar to reported in Bolívar state [9], most of the women are from Angostura del Orinoco and Sifontes municipality, which perhaps be related to the continuous migration of individuals from the community to gold mining areas, contributing to the malaria transmission [19, 21, 31].
The clinical manifestations were similar to those reported by other authors [29]. In contrast to findings in Colombia by Tobón et al. [29], in this study headache was more frequent in women with P. vivax compared to P. falciparum. This, together with the high frequency of fever, supports the practice of performing malaria diagnostic tests at prenatal check-ups, favouring timely diagnosis in highly endemic areas as has been suggested before [16, 34]. Indeed, early malaria diagnosis and treatment reduce maternal mortality [35]. Severe anaemia is responsible for around 50% of the complications of MiP in endemic areas with intense and stable transmission [31]. In this study, 84.6% of women presented Hb alterations that ranged from mild to severe, with severe anaemia as the most frequent malaria complication among all women (23%), in agreement with several studies [32, 36], but in contrast with results from Colombia, where mild-to-moderate anaemia and severe anaemia were observed in 68% and 2.9%, respectively [10].
The most important finding of this study is the high prevalence of maternal and foetal complications (44%), with preterm delivery, oligohydramnios, abortion, and foetal death as the most frequent complications. Almost all of them in women with malaria by P. vivax, an infection usually considered less severe as compared to P. falciparum malaria. This is assumed to be related to the lack of placental sequestration in P. vivax infections and the parasite tropism for reticulocytes accounting for a milder form of anaemia [37]. Similar to a previous study carried out in Bolívar state [9], a higher proportion of abortions was registered in pregnant women infected with P. vivax. In this study, the prevalence of preterm delivery regardless other complications was higher than reported by other studies (18.6% vs. 7.5%- 8.5%) [38, 39]; another study in Colombia reported a higher rate of preterm delivery (70.8%), however, only included hospitalized pregnant women [29]. Anaemia has been associated with a higher proportion of preterm delivery [40], which could explain the high frequency of this complication in the studied population.
On the other hand, the number of women with oligohydramnios and intrauterine growth restriction was lower than documented by another study (40 and 80%, respectively) in Peru [41]. Herein, four spontaneous abortion and three foetal deaths were recorded in 55 studied women. This contrast with the mortality rate of 21.1 deaths per 1,000 live births reported in the country for 2016 [42]Although pregnant women have parasitaemia ten times higher than non-pregnant women, due to inadequate immune response [43], in areas of stable malaria transmission, women of childbearing age have acquired partial immunity, that protects them to some extent against acute clinical disease [44]. Whether the studied pregnant women have acquired humoral immunity or not, were beyond the scope of this study, but should be further explored.
Due mainly to logistical and financial constraints, this study has some limitations. First, the clinical and epidemiological characteristics of MiP are described only in a single diagnostic centre. Thus, additional studies are needed to investigate the impact of malaria on maternal-foetal health in different sentinel centres in the country. Second, complete paraclinical examinations were carried out only in a subset of the women. Finally, the presence of maternal-foetal complications is unknown for several women.