Fetal and infant death in mono- and dizygotic twins in England and Wales 1982-91
Foundation
for the Study of Infant Deaths, Unit of Perinatal and Paediatric
Epidemiology, Department of Public Health,
University of Liverpool,
Liverpool L69 3GB
Correspondence to: Emeritus Professor POD Pharoah.
Accepted 26 November
1998
AIM
To quantify
the level of risk for stillbirth and infant death in singleton
compared with twin pregnancies, using national data; to determine the
independent effects of zygosity, sex, and birthweight on these
risks in twin pregnancies.
METHODSA
retrospective national study was carried out of all singleton and twin
birth and death registrations in England and Wales 1982-91, according
to sex and birthweight group. Weinberg's rule was applied to the twin
pairs to differentiate mono- from dizygotic twins. Relative risks for
mono- compared with dizygous twins for both twins being stillbirths and
for one of the pair being a stillbirth were determined. For twins where
one was stillborn and the other live born, the relative risk of
neonatal and infant mortality in the surviving co-twin was determined.
RESULTSThere
were 6 563 834 registered singletons and 70772 registered twin pairs
for the period under study. Monozygotic twins had a relative risk of:
18.91 (95% CI 12.48-28.64) for both twins being stillborn; 1.63 (95%
CI 1.48-1.79) for one twin being a stillbirth; and 2.26 (95% CI
1.45-3.52) for the live born co-twin dying as a neonate. When both
twins were live born and among singletons, the odds ratio for neonatal
mortality of being male was 1.41 (95% CI 1.37-1.45) and there was a
highly significant negative association with birthweight. After
adjusting for birthweight group and sex, twins had a reduced neonatal
mortality compared with singletons: odds ratio 0.91 (95% CI
0.85-0.96).
CONCLUSIONSFetal
death in one of monozygotic twins has serious implications for survival
of the co-twin. Monochorionicity is probably the essential feature of
the increased risk to the co-twin. It is imperative that all fetal
deaths in multiple pregnancies are recorded and chorionicity determined
if parents are to be adequately counselled.
Keywords: zygosity; twins; stillbirths; monochorionicity
© 1999 by Archives of Disease in Childhood
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