The implications of a false positive second-trimester serum screen for Down syndrome.
OBJECTIVE
To investigate the genetic and obstetric implications of false positive Down syndrome serum screening results.


METHODS
The study population comprised 162774 women underwent triple marker screening in the Ontario Maternal Serum Screening program between October 1995 and September 1998, with outcomes obtained from the Canadian Institute of Health Information. The study compares the incidence of chromosomal abnormalities other than Down syndrome in screen positive women with background incidence from the literature. It also compares the risks of having a fetus with congenital abnormalities or of developing obstetric complications in 11549 screen positive women with their matched controls.


RESULTS
A higher incidence of trisomy 13 (12.4 per 10000) was seen in screen positive women; the incidence of other chromosomal abnormalities in screen positive women was not increased relative to the general population. The higher incidence of trisomy 13 may have been biased by the selective uptake of amniocentesis in women who had high risks for Down syndrome or abnormal ultrasound findings. Incidences of fetal congenital abnormality in screen positive and negative women were similar. Women who screened positive for Down syndrome had increased risk of spontaneous fetal loss (odds ratio 1.80; 95% confidence interval 1.54, 2.07) but no other obstetric complications.


CONCLUSIONS
Among women who screened positive for Down syndrome, we found a higher number of spontaneous fetal losses and a possibly higher risk of having a fetus with trisomy 13. We did not find an increased risk for other chromosomal abnormalities, congenital abnormalities, or other adverse obstetric outcomes.
Summers
Anne M
AM
Department of Genetics, North York General Hospital, Toronto, Ontario, Canada. asummers@nygh.on.ca
Huang
Tianhua
T
Meier
Chris
C
Wyatt
Philip R
PR
D000022:Abortion, Spontaneous; D000328:Adult; D000649:Amniocentesis; D015415:Biomarkers / Q000097:blood; D016022:Case-Control Studies; D006063:Chorionic Gonadotropin / Q000097:blood*; D025063:Chromosome Disorders / Q000175:diagnosis; D002882:Chromosomes, Human, Pair 13; D003937:Diagnosis, Differential; D004314:Down Syndrome / Q000175:diagnosis*; D004964:Estriol / Q000097:blood*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D011247:Pregnancy; D011262:Pregnancy Trimester, Second / Q000097:blood; D011296:Prenatal Diagnosis; D014314:Trisomy / Q000175:diagnosis; D000509:alpha-Fetoproteins / Q000032:analysis*
D015415:Biomarkers; D006063:Chorionic Gonadotropin; D000509:alpha-Fetoproteins; D004964:Estriol