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.
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.