Is routine fetal karyotyping necessary for patients undergoing amniocentesis for elevated maternal serum α-fetoprotein?

OBJECTIVE: The object of the study was to determine the necessity of routine fetal karyotyping in patients undergoing amniocentesis for elevated maternal serum alpha-fetoprotein (AFP). METHODS: Data were collected retrospectively on patients under age 35 who underwent amniocentesis for elevated maternal serum AFP at the University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey, between 1 January 1986 and 31 March 1995. A total of 537 patients with maternal serum AFP values greater than 2.5 multiples of the median were included in the study. RESULTS: Of 509 patients in the group with normal amniotic fluid AFP, 505 had a normal karyotype (specificity 94.9%, negative predictive value 99.2%). One of 28 patients in the group with an elevated amniotic fluid AFP demonstrated an abnormal karyotype (sensitivity 20%, positive predictive value 3.6%). CONCLUSIONS: Routine fetal chromosomal analysis of amniotic fluid amniocytes may not be necessary in patients with a normal level of amniotic fluid AFP. A fetal karyotype is recommended in those patients with an elevated amniotic fluid AFP.