Arch Dis Child Fetal Neonatal Ed 2001;84:F79-F84 ( March )

Evidence of selection bias in preterm survival studies: a systematic review

D J Evans, M I Levene

Centre for Reproduction, Growth and Development, University of Leeds, D Floor Clarendon Wing, The General Infirmary at Leeds, Leeds LS2 9NS, UK

Correspondence to: Dr Evans, Neonatal Intensive Care Unit, Southmead Hospital, Bristol BS10 5NB, UK evans_d{at}southmead.swest.nhs.uk

Accepted 26 October 2000

OBJECTIVETo determine by how much selection bias in preterm infant cohort studies results in an overestimate of survival.
DESIGNSystematic review of studies reporting survival in infants less than 28 weeks of gestation published 1978-1998. Studies were graded according to cohort definition: A, stillbirths and live births; B, live births; C, neonatal unit admissions. Proportions of infants surviving to discharge were calculated for each week of gestation.
RESULTSSixty seven studies report data on 55 cohorts (16 grade A, 23 grade B, 16 grade C). Studies that are more selective report significantly higher survival between 23 and 26 weeks of gestation (grade C > grade B > grade A, p < 0.01), exaggerating survival by 100% and 56% at 23 and 24 weeks respectively.
CONCLUSIONTo minimise the potential for overestimating survival around the limits of viability, future studies should endeavour to report the outcome of all pregnancies for each week of gestation (terminations, miscarriages, stillbirths, and all live births).


Keywords: preterm; survival; selection bias

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© 2001 by Archives of Disease in Childhood
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