Testing for Open Neural Tube Defects and Trisomy 18

Detection Rate (DR):
Also known as sensitivity, is the probability that a fetus affected with Down syndrome will be detected by the prenatal screening test.

False Positive Rate (FPR):
The proportion of women with unaffected pregnancies who have positive results.

Pregnancy Dating
Ultrasound (U/S) dating is more accurate than LMP; a dating U/S will lower the FPR.

All pregnancies have a 2-3% risk for any birth defect which may or may not be detected by prenatal screening.

Adapted from:
1. Wald NJ, et al. First and second trimester antenatal screening for Down’s syndrome: the results of the Serum, Urine and Ultrasound Screening Study (SURUSS). J Med Screen 2003; 10:56-104.

2. Malone FD, et al. First- and Second-Trimester Evaluation of Risk (FASTER)
Research Consortium. First-trimester or second-trimester screening, or both, for Down’s syndrome. N Engl J Med. 2005; 353:2001-11.
 
3. Wapner R, et al. First trimester screening for trisomies 21 and 18. N Engl J Med 2003; 349:1405 -1413.

4. Summers AS, et al. Maternal serum screening in Ontario using the triple marker test. J Med Screen 2003; 10:107-11.

5. American College of Obstetricians and Gynecologists. Clinical Management
Guidelines for obstetricians-gynecologists. ACOG Practice Bulletin No. 44, Obstet Gynecol 2003; 102:203-211.

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