Research article

Does the risk of cerebral palsy increase or decrease with increasing gestational age?

K S Joseph¹ , Alexander C Allen^1,2 , Samawal Lutfi² , Lynn Murphy-Kaulbeck³ , Michael J Vincer² and Ellen Wood⁴

¹Perinatal Epidemiology Research Unit, Departments of Obstetrics & Gynecology and of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada

²Division of Neonatal-Perinatal Medicine, Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada

³Division of Maternal-Fetal Medicine, Department of Obstetrics & Gynecology, Dalhousie University, Halifax, Nova Scotia, Canada

⁴Division of Neurology, Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada

author email corresponding author email

BMC Pregnancy and Childbirth 2003, 3:8doi:10.1186/1471-2393-3-8

Published:	23 December 2003

Abstract

Background

It is generally accepted that the risk of cerebral palsy decreases with increasing gestational age of live born infants. However, recent studies have shown that cerebral palsy often has prenatal antecedents including congenital malformations, vascular insults and maternal infection. Cerebral palsy is therefore better viewed as occurring among fetuses, rather than among infants. We explored the epidemiologic implications of this change in perspective.

Methods

We used recently published data from Shiga Prefecture, Japan and from North-East England to examine the pattern of gestational age-specific rates of cerebral palsy under these alternative perspectives. We first calculated gestational age-specific rates of cerebral palsy as per convention, by dividing the number of cases of cerebral palsy identified among live births within any gestational age category by the number of live births in that gestational age category. Under the alternative formulation, we calculated gestational age-specific rates of cerebral palsy by dividing the number of cases of cerebral palsy identified among live births within any gestational age category by the number of fetuses who were at risk of being born at that gestation and being afflicted with cerebral palsy.

Results

Under the conventional formulation, cerebral palsy rates decreased with increasing gestational age from 63.9 per 1,000 live births at <28 weeks gestation to 0.9 per 1,000 live births at 37 or more weeks gestation. When fetuses were viewed as potential candidates for cerebral palsy, cerebral palsy rates increased with increasing gestational age from 0.08 per 1,000 fetuses at risk at <28 weeks gestation to 0.9 per 1,000 fetuses at risk at 37 or more weeks gestation.

Conclusions

The fetuses-at-risk approach is the appropriate epidemiologic formulation for calculating the gestational age-specific rate of cerebral palsy from a causal perspective. It shows that the risk of cerebral palsy increases as gestational duration increases. This compelling view of cerebral palsy risk may help refocus research aimed at understanding and preventing cerebral palsy.