Failure to obtain reliable retrospective determination of chorion type using parent information: confirmation with...

Following the Derom et al. paper recently published in Twin Research (2003, 6, 19-21), we investigated our French sample, studying the retrospective validity of information given by parents to determine the chorion type of their monozygotic twins. The sample included 44 MZ pairs of known chorion type. Chorion type was established by a pathologist specialising in the study of placenta and zygosity diagnosis using molecular genetic techniques. Results show that of the parents who had information, there was a high level of uncertainty of the chorion type. It therefore seems impossible to obtain valid retrospective determination from parents and the only solution is to have accurate information in the birth records.