PRENATALDIAGNOSIS, VOL. 14: 947-951 (1994) SECOND-TRIMESTER DIURNAL VARIATION OF MATERNAL SERUM ALPHA-FETOPROTEIN, HUMAN CHORIONIC GONADOTROPIN, AND UNCONJUGATED OESTRIOL: IS IT PRESENT AND DOES IT AFFECT THE PREDICTION OF A PATIENT’S RISK FOR FETAL DOWN SYNDROME? NANCY C. ROSE*, JACOB A. CANICKt, GEORGE J. KNIGHTS, ANDREA PULKKINEN$, M. B. TUMBERT, MICHAEL T. MENNUTI* AND GLENN E. PALOMAKIS *Division of Reproductive Genetics, Department of Obstetrics and Gynecology, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania, U. S.A.; ?Department of Pathology and Laboratory Medicine, Women and Infants Hospital, Brown University, Providence, Rhode Island, U. S. A,; SFoundationfor Blood Research, Scarborough, Maine, U. S.A. Received March 1994 Revised May I994 Accepted May I994 SUMMARY Both a cross-sectional and a longitudinal study were performed to investigate whether or not the collection time should be taken into consideration when generating a patient’s risk for fetal Down syndrome with multiple marker screening. Diurnal variations of third-trimester alpha-fetoprotein (AFP) levels and first-trimester human chorionic gonadotropin (hCG) levels have been previously reported. In addition, large episodic fluctuations of conjugated and unconjugated oestrioi (uE3) as well as a diurnal variation have also been reported in the third trimester. If the levels of these analytes routinely fluctuate during the day, they could affect a patient’s risk calculation for fetal Down syndrome. The longitudinal study evaluated ten non-diabetic women who underwent sequential sampling for AFP, hCG, and uE3. The cross-sectional study evaluated 1953 patients for these three markers whose time of sampling was recorded between 8-00 a.m. and 5.59 p.m. Using either study design, no significant effect was seen in the median MOM levels of the screening analytes as a function of the time of day. KEY w o m s D i u r n a 1 variation, alpha-fetoprotein, human chorionic gonadotropin, unconjugated oestriol. INTRODUCTION The measurement of maternal serum alpha- fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated oestriol (uE3), in com- bination with maternal age, is currently used as a Addressee for correspondence: Nancy C. Rose, MD, Div- ision of Reproductive Genetics, Department of Obstetrics and Gynecology, University of Pennsylvania Medical Center, 3400 Spruce Street, 2000 Courtyard Building, Philadelphia, PA 19104, U.S.A. 01994 by John Wiley & Sons, Ltd. CCC 01 97-3851/94/100947-05 second-trimester screening test for fetal Down syndrome. Screening protocols need to include the date at which the sample was drawn in order to calculate the gestational age and, subsequently, the patient’s risk, but the time of sampling is not generally taken into consideration. If the levels of any of the markers fluctuated significantly in a predictable pattern during the day, then the timing of the serum sampling would also need to be taken into account for risk calculation. Diurnal variation of third-trimester AFP levels (Houghton er al.,