title: Childbearing and the risk of leukemia in Sweden.
abstract: OBJECTIVE
  The possible influence of childbearing on the development of leukemias in females has received little attention, in spite of consistent findings of lower incidence rates in females than in males. A nested case-control study was undertaken to explore if parity and age at first birth affect the risk of developing these malignancies.
  
  
  METHODS
  In a nationwide cohort defined by a population-based Fertility Register, we identified 356 women with chronic myeloid leukemia (CML), 819 with acute nonlymphocytic leukemia (ANLL), and 179 with acute lymphocytic leukemia (ALL). For each case, five age-matched controls were selected. Odds ratios were estimated by conditional logistic regression analyses.
  
  
  RESULTS
  There was some evidence of weak negative associations between parity and age at first birth for CML. Compared to nulliparous women there was a tendency of a temporal risk reduction of CML for the first 10 years following a delivery. The risk of ANLL was slightly lower in parous compared to nulliparous women. Neither parity nor age at first birth was related to the risk of ALL.
  
  
  CONCLUSIONS
  We conclude that if pregnancy-related hormonal or immunological factors have an effect on the development of leukemia, it is minor and confined to the myeloid types, chiefly CML. Our study gives some support for treating the leukemias as separate entities based on both cell lineage and form in future etiologic studies.
authors.affiliation: Department of Medical Epidemiology, Karolinska Institutet, Stockholm, Sweden. karin.ekstrom@mep.ki.se
authors.forename: Karin
authors.initials: K
authors.lastname: Ekström
authors.forename: Joanne
authors.initials: J
authors.lastname: Wuu
authors.forename: Chung-Cheng
authors.initials: CC
authors.lastname: Hsieh
authors.forename: Bengt
authors.initials: B
authors.lastname: Glimelius
authors.forename: Mats
authors.initials: M
authors.lastname: Lambe
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D016022:Case-Control Studies; D015331:Cohort Studies; D016001:Confidence Intervals; D004198:Disease Susceptibility; D005260:Female; D006801:Humans; D015994:Incidence; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000453:epidemiology* / Q000209:etiology; D015470:Leukemia, Myeloid, Acute / Q000453:epidemiology* / Q000209:etiology; D008423:Maternal Age; D008875:Middle Aged; D016017:Odds Ratio; D010298:Parity; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000453:epidemiology* / Q000209:etiology; D011247:Pregnancy; D012016:Reference Values; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology