Effect of normal MSAFP screening on maternal age for genetic amniocentesis.
Routine maternal serum alpha-fetoprotein (MSAFP) screening for neural tube defects is considered by many to be standard obstetrical care, and recently many have encouraged this test to screen for Trisomy-21 (Down's syndrome). We questioned whether, after a normal MSAFP screen, the risk of Trisomy-21 decreases enough to warrant modifying the recommended age for genetic amniocentesis for Down's syndrome. A logistic regression was developed which, using reported values for sensitivity and specificity for MSAFP detection of Trisomy-21 and assuming a constant threshold risk in opting for amniocentesis, indicates that genetic amniocentesis for Trisomy-21 may be deferred in some women who have a normal MSAFP screening. Sensitivity analysis of varying thresholds for a normal MSAFP demonstrates that a 37 year old woman with a median MSAFP level has the same risk for Trisomy-21 as an unscreened women who is 4.5 years younger. An abnormal MSAFP is useful in screening for neural tube defects and possibly for Trisomy-21. A normal MSAFP may allow for delaying the potentially risky amniocentesis in otherwise low-risk pregnancies.
Ganiats
T G
TG
Department of Community and Family Medicine, UC San Diego School of Medicine, La Jolla 92093.
Berry
C C
CC
Fullerton
J T
JT
D000328:Adult; D000367:Age Factors; D000649:Amniocentesis; D004314:Down Syndrome / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008423:Maternal Age; D009436:Neural Tube Defects / Q000175:diagnosis; D011247:Pregnancy; D011296:Prenatal Diagnosis; D011336:Probability; D012044:Regression Analysis; D012307:Risk Factors; D000509:alpha-Fetoproteins / Q000032:analysis*
D000509:alpha-Fetoproteins