Perinatal Risk Factors for Childhood Leukemia
Abstract: The aim of the studies described in this thesis was to assess the association between certain perinatal factors and the risk of childhood lymphatic and myeloid leukemia and infant leukemia. The five studies presented were all conducted in Sweden as population-based case-control studies. All cases were born and diagnosed between 1973-89 with leukemia up to the age of 16 years. A control was individually matched to each case. As Down’s syndrome entails a major risk for childhood leukemia, children with Down’s syndrome were excluded. The studies comprised a total of 652 cases, 47 of whom were diagnosed before the age of one year. Exposure data were extracted blindly from antenatal, obstetric, pediatric and other standardized medical records.No association was found between prenatal exposure to ultrasound or diagnostic x-ray and childhood lymphatic or myeloid leukemia. Infant leukemia was associated with prenatal exposure to x-ray. A history of maternal lower genital tract infection significantly increased the risk of childhood leukemia, especially among children diagnosed at four years or older or in infancy. Factors such as young maternal age, and mothers working with children or in the health sector were associated with infant leukemia. Resuscitation with 100% oxygen with a face-mask and bag directly postpartum was associated with an increased risk of childhood lymphatic leukemia. The oxygen-related risk further increased if the manual ventilation lasted for three minutes or more. There was no association between lymphatic or infant leukemia and supplementary oxygen later in the neonatal period or other birth-related factors. Low Apgar scores at one and five minutes were associated with a non-significantly increased risk of lymphatic leukemia, and were significantly associated with infant leukemia.Previously reported relations between childhood leukemia and exposures such as maternal diagnostic x-ray and birth related factors could not be confirmed by these studies. However, the present studies indicate that events during pregnancy or during the neonatal period are associated with increased risks of childhood and infant leukemia. These events can either be non-specific, such as exposure to maternal lower genital tract infection, or specific, such as the use of supplementary oxygen directly postpartum.
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