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Correspondence |
Department of Obstetrics and Gynaecology, University of Fukui, Japan
Department of Obstetrics and Gynaecology,University of Fukui, Matsuoka-cho, Yoshida-gun, Fukui 910-1193, Japan. E-mail: kojigyne{at}fmsrsa.fukui-med.ac.jp
We read with great interest the article by Isohanni et al (2005), which investigated subtle motor, emotional, cognitive and behavioural abnormalities as predictors of schizophrenia. The authors concluded that these are not useful predictors of illness. However, Isohanni et al did not investigate gestational age as a predictor of psychological abnormalities in later life. This has recently been used as a predictor in some cohort studies (Thompson et al, 2001; Gale & Martyn, 2004; Wiles et al, 2005), and is obstetrically one of the most important predictors of childhood outcomes that are also related to psychological abnormalities in later life (Thompson, 2001; Gale & Martyn, 2004; Cunningham et al, 2005). We feel strongly that birth cohort studies of psychological abnormalities in later life should include gestational week at birth. The study of Isohanni et al would have benefited from inclusion of this variable.
EDITED BY KIRIAKOS XENITIDIS and COLIN CAMPBELL
REFERENCES
Cunningham, E. G., Leveno, K. J., Bloom, S. L., et al (2005) Williams Obstetrics (22nd edn). New York: McGraw-Hill.
Gale, C. R. & Martyn C. N. (2004) Birth
weight and later risk of depression in a national birth cohort.
British Journal of Psychiatry,
184, 28-33.
Isohanni, M., Lauronen, E., Moilanen, K., et al
(2005) Predictors of schizophrenia. Evidence from the
Northern Finland 1966 Birth Cohort and other sources. British
Journal of Psychiatry, 187 (suppl.
48), s4-s7.
Thompson, C., Syddall, H., Rodin, I., et al
(2001) Birth weight and the risk of depressive disorder in
late life. British Journal of Psychiatry,
179, 450
-455.
Wiles, N. J., Peters, T. J., Leon, D. A., et al
(2005) Birth weight and psychological distress at age 45-51
years. Results from the Aberdeen Children of the 1950s cohort study.
British Journal of Psychiatry,
187, 21-28.
Department of Psychiatry, University of Oulu, PO Box 5000, Finland. E-mail: matti.isohanni{at}oulu.fi
Department of Psychiatry, University of Oulu, Finland
We welcome the comments of Shukinami et al but it is important to realise the basic theoretical and practical difference between a risk factor and prediction of illness in the premorbid phase. When exposures are common (as are many obstetric complications) but incidence ratios of the illness are not high and outcomes fairly rare (as is schizophrenia), prediction of future disease is difficult.
Abnormal gestational age may or may not be a subtle risk factor for schizophrenia. This has been analysed in a recent meta-analysis (Cannon et al, 2002) of eight prospective population-based studies of the association between obstetric complications and schizophrenia. Gestational age under 37 weeks was weakly associated with schizophrenia (odds ratio = 1.22, 95% CI 0.90-11.65). The results within the Northern Finland 1966 Birth Cohort were similar (Jones et al, 1998).
Our review mentioned abnormal foetal growth and development as a potential risk factor for schizophrenia, as did Cannon et al, but the predictive power of abnormal foetal growth is weak as it is a rather common phenomenon. Prediction in this situation is not easy at the population level. Our aim was to describe the best known risk factors for schizophrenia, which is why we did not conduct a detailed analysis of gestational age.
The references included in the letter of Shukinami et al suggest that the association of gestational age with other mental disorders may be stronger than for schizophrenia.
REFERENCES
Cannon, M., Jones, P. B. & Murray, R. M.
(2002) Obstetric complications and schizophrenia: historical
and meta-analytic review. American Journal of
Psychiatry, 159, 1080
-1092.
Jones, P. B., Rantakallio, P., Hartikainen, A.-L., et
al (1998) Schizophrenia as long-term outcome of
pregnancy, delivery, and perinatal complications: a 28-year follow-up of the
1966 North Finland general population birth cohort. American
Journal of Psychiatry, 155, 355
-364.
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