[Effects of birth order, maternal abortion and mode of delivery on childhood acute leukemia risk: a meta-analysis]

To evaluate the associations between birth order, maternal abortion and mode of delivery and childhood acute leukemia risk.Multiple electronic databases were searched to identify relevant studies up to March 2013 using the search terms "childhood leukemia", "acute lymphoblastic leukemia", "acute myeloid leukemia","birth order", "abortion", "miscarriage", "cesarean", "birth characteristics" and "prenatal risk factor". Data from cohort and case-control studies were analyzed using the Stata software.Twenty-three studies were included in this meta-analysis according to the selection criteria. No significant associations were identified for birth order and mode of delivery (birth order = 2: OR = 0.97, 95%CI: 0.89-1.05; birth order = 3: OR = 1.00, 95%CI: 0.91-1.11; birth order ≥ 4: OR = 1.02, 95%CI: 0.87-1.20; mode of delivery: OR = 1.05, 95%CI: 0.96-1.15). However, there was a significant association between maternal abortion and childhood acute leukemia risk (spontaneous abortion: OR = 1.21, 95%CI: 1.05-1.41; induced abortion: OR = 1.23, 95%CI: 1.07-1.43). Furthermore, the stratified analysis by disease subtypes showed that spontaneous and induced abortions were significantly associated with the risks of childhood acute myeloid leukemia (OR = 1.71, 95%CI: 1.09-2.70) and acute lymphoblastic leukemia (OR = 1.23, 95%CI: 1.05-1.42), respectively.This meta-analysis revealed that maternal abortion might contribute to the childhood acute leukemia risk.