Thrombocytopaenia in pregnant women with malaria on the Thai-Burmese border

Background Haematological changes associated with malaria in pregnancy are not well documented, and have focused predominantly on anaemia. Examined here is thrombocytopaenia in pregnant women infected with Plasmodium falciparum or Plasmodium vivax in a low transmission area on the north-western border of Thailand. Methods In this observational study we reviewed the platelet counts from routine complete blood count (CBC) in a cohort of healthy and malaria infected Karen pregnant women attending weekly antenatal clinics. A platelet count of 75,000/μL was the threshold at 2 standard deviations below the mean for healthy pregnant women used to indicate thrombocytopenia. Differences in platelet counts in non-pregnant and pregnant women were compared after matching for age, symptoms, malaria species and parasitaemia. Results In total 974 pregnant women had 1,558 CBC measurements between February 2004 and September 2006. The median platelet counts (/μL) were significantly lower in patients with an episode of falciparum 134,000 [11,000–690,000] (N = 694) or vivax malaria 184,000 [23,000–891,000] (N = 523) compared to healthy pregnant women 256,000 [64,000–781,000] (N = 255), P < 0.05 for both comparisons. Plasmodium falciparum and P. vivax caused a 34% (95% CI 24–47) and 22% (95% CI 8–36) reduction in platelet count, respectively. Pregnant compared to non pregnant women were at higher risk OR = 2.27 (95%CI 1.16–4.4) P = 0.017, for thrombocytopaenia. Platelets counts were higher in first compared with subsequent malaria infections within the same pregnancy. Malaria associated thrombocytopaenia had a median [range] time for recovery of 7 [2–14] days which did not differ by antimalarial treatment (P = 0.86), or species (P = 0.63) and was not associated with active bleeding. Conclusion Pregnant women become more thrombocytopenic than non-pregnant women with acute uncomplicated malaria. Uncomplicated malaria associated thrombocytopaenia is seldom severe. Prompt antimalarial treatment resulted in normalization of platelet counts within a week.