Counselling implications of chromosomal abnormalities other than trisomy 21 detected through a maternal serum screening programme

Objective To identify counselling requirements, we reviewed the frequency and type of non-trisomy 21 chromosome abnormalities found at amniocentesis after maternal serum screening for Down's syndrome.

Design The study involved a review of the cytogenetic results of amniocenteses performed because of a raised maternal serum screening risk.

Setting The maternal serum screening and amniocenteses were performed at hospitals in the Yorkshire region.

Sample 1715 amniocenteses were performed as a result of a raised maternal serum screening risk for the period 1990 to 1993.

Methods The cytogenetic results were classified into the main categories of numerical and structural chromosomal abnormalities.

Main outcome measures The nature and frequency of abnormal cytogenetic results were identified in which parental samples were required in order to determine if the abnormal finding was de novo or familial and/or for which specialist genetic counselling was required.

Results Sixty-nine pregnancies of 1715 amniocenteses were identified with a chromosomal abnormality (4.0%): 35 (2.0%) with trisomy 21 and 34 (2.0%) with another chromosomal abnormality. For 20 of these 34 abnormalities, parental karyotypes were required and in 29 of the 34 specialist genetic counselling was required.

Conclusions Women undergoing maternal serum screening and, in particular, those proceeding to amniocentesis, should be informed that there is an equal chance that a chromosomal abnormality other than trisomy 21 will be found at amniocentesis, the nature of which usually requires parental samples and specialist counselling.