How the effect of maternal age on the risk of childhood leukemia changed over time in Sweden, 1960-2004.
BACKGROUND
Previous studies on the association between maternal age and risk of childhood leukemia found inconsistent results.


OBJECTIVE
We aimed to assess whether there is an association between maternal age and risk of childhood leukemia and whether such an association is modified by maternal year of birth.


METHODS
By linking nationwide Swedish registers, we analyzed leukemia incidence among all children between 1 and 5 years of age born between 1960 and 1999. We estimated incidence time trends by child year of birth (overall and stratified by maternal age) and incidence rate ratios (RRs) for maternal age groups stratified by maternal birth cohort. We tested the interaction between maternal age and child year of birth through the likelihood ratio test between nested Poisson regression models.


RESULTS
We observed 1,562 leukemia cases. The overall annual percent change (APC) was 1.00 [95% confidence interval (CI), 0.51 to 1.49]. Stratifying by maternal age classes, APCs decreased from 1.66 (0.68 to 2.65) for mothers <or= 24 years to 0.23 (-0.93 to 1.40) for mothers >or= 35 years at delivery. RRs for children born to the oldest with respect to the youngest mothers were 2.42 (1.31 to 4.67), 1.68 (1.00 to 2.72), 1.34 (0.87 to 2.01), and 0.87 (0.46-1.54) for mothers born in 1930-1934, 1940-1944, 1950-1954, and 1960-1964, respectively.


CONCLUSIONS
Childhood leukemia risk increased with maternal age for mothers born in the past, whereas maternal age had no effect on this risk for mothers born more recently. This finding may explain the inconsistency of previous studies and suggests that leukemia risk may be related to an environmental factor to which women's exposure has changed over time.
Maule
Milena Maria
MM
Cancer Epidemiology Unit, Center for Experimental Research and Medical Studies and Center for Oncologic Prevention in Piedmont, University of Turin, Turin, Italy. milena.maule@cpo.it
Vizzini
Loredana
L
Czene
Kamila
K
Akre
Olof
O
Richiardi
Lorenzo
L
D000328:Adult; D005260:Female; D049673:History, 20th Century; D049674:History, 21st Century; D006801:Humans; D007938:Leukemia / Q000453:epidemiology* / Q000266:history; D008423:Maternal Age; D011247:Pregnancy; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult