Counseling problems when twins are discovered at genetic amniocentesis.

With the increased use of routine ultrasonography at the time of genetic amniocentesis, twins are increasingly likely to be discovered at the time when the procedure is to be carried out. In the presence of twins the likelihood of finding an abnormality may be significantly increased, but at the same time problems such as discordance between the twins for the abnormality, or the inability to test both twins may occur. This altered situation may affect the parents' decision as to whether or not to undertake amniocentesis, and the need for additional counseling prior to proceeding with the amniocentesis is stressed.