ABSTRACT
Screening for and detecting fetal abnormality when there is a multiple gestation is both difficult and complicated. Simple tests like serum screening cannot be used, because no laboratory would be able to predict the combination of one affected and one non-affected infant. Nevertheless, with dichorionic twins (twins from two separate eggs), any age related risk of, for example, Down’s syndrome would be the risk for either one of the children being affected. This would mean that the risk of a woman having one or more abnormal fetuses would be doubled for twins, trebled for triplets and so on. Whilst it is recognised that twin amniocentesis does carry additional risk over the procedure carried out for a singleton, this may be what the woman requests and should be carried out for her. Nuchal fold thickness would seem to be appropriate as a non-invasive alternative.
