Intrauterine growth restriction in like-sex twins discordant for structural defects.
BACKGROUND
An increased risk for intrauterine growth restriction in the affected member of like-sex twin pairs discordant for hypospadias has been reported. The purpose of this study was to document patterns of birth weight disparities in like-sex twins discordant for a variety of structural defects in order to determine if this is a general phenomenon seen in twins who are discordant for any malformation, is seen only in pairs discordant for certain specific malformations, or is unique to hypospadias.


METHODS
Data were extracted from the Latin American Collaborative Study of Congenital Malformations (ECLAMC). Between 1967 and 1999, all like-sex twin pairs discordant for hypospadias or any other isolated defect that met the criteria of at least 5 discordant pairs for which birth weight was available on both twins were selected. All nonmalformed like-sex twin pairs in the ECLAMC data base collected over the same study years were selected as controls.


RESULTS
A total of 216 discordant malformed like-sex twin pairs in 13 defect categories and 328 nonmalformed like-sex twin pairs met the criteria for inclusion. The proportion of affected infants who were > or =20% smaller than their co-twin was statistically significantly different from controls for hypospadias, heart defects, anencephaly, and esophageal atresia.


CONCLUSIONS
Intrauterine growth restriction seen in the affected member of like-sex twin pairs discordant for hypospadias is not unique, but occurs as well in at least 3 additional structural malformations.
Department of Pediatrics, Division of Dysmorphology and Teratology, University of California San Diego School of Medicine, La Jolla, 92103, USA. chchambers@ucsd.edu
Christina D
CD
Chambers
Eduardo E
EE
Castilla
Ieda
I
Orioli
Kenneth L
KL
Jones
D001724:Birth Weight; D016022:Case-Control Studies; D000013:Congenital Abnormalities / Q000453:epidemiology; D005260:Female; D005317:Fetal Growth Retardation; D006130:Growth Disorders / Q000235:genetics; D006801:Humans; D007231:Infant, Newborn; D007621:Karyotyping; D007843:Latin America / Q000453:epidemiology; D011247:Pregnancy; D012727:Sex Characteristics; D014427:Twins