- Full (HTML) - Full (PDF) - Related EHP Articles - Purchase This Issue

Milena Maria Maule,¹ Loredana Vizzini,¹ Kamila Czene,² Olof Akre,^1,3 and Lorenzo Richiardi¹

¹Cancer Epidemiology Unit, Center for Experimental Research and Medical Studies and Center for Oncologic Prevention in Piedmont, University of Turin, Turin, Italy; ²Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; ³Clinical Epidemiology Unit, Department of Medicine, Karolinska University Hospital, Karolinska Institutet, Stockholm, Sweden

Abstract
Background: Previous studies on the association between maternal age and risk of childhood leukemia found inconsistent results.

Objectives: 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 ≤ 24 years to 0.23 (–0.93 to 1.40) for mothers ≥ 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.

Key words: childhood leukemia, epidemiology, maternal age, rate ratios, time trends. Environ Health Perspect 117:299–302 (2009) . doi:10.1289/ehp.11938 available via http://dx.doi.org/ [Online 7 November 2008]

Address correspondence to M.M. Maule, Cancer Epidemiology Unit, University of Turin, Via Santena 7, 10126, Turin, Italy. Telephone: 390116334628. Fax: 390116334664. E-mail: milena.maule@cpo.it

We are grateful to F. Merletti for useful discussions and suggestions.

This project was supported by the Piedmont Region, the Oncology Special Project, Compagnia di San Paolo/FIRMS, and the Italian Association for Cancer Research (AIRC) . O.A. is supported by the Stockholm County Council and Karolinska Institutet and by a UICC Yamagiwa-Yoshida Memorial International Cancer Study Grant.

The authors declare they have no competing financial interests.

Received 15 July 2008 ; accepted 7 November 2008.