Prenatal Testing Summary

    SCREENING   DIAGNOSTIC
First Trimester Combined Screening(FTS)1 Maternal Serum Screening(MSS) Routine 2nd trimester Ultrasound Chorionic Villus Sampling (CVS) Amniocentesis
How it is Done Blood Test +Ultrasound Blood test Ultrasound Transvaginal or transabdominal procedure. Transabdominal procedure
Preferred Timing 11-13 6/7 weeks 15-19 6/7 weeks 18-20 weeks 11-13 weeks

> 15 weeks (commonly 15-16 wks)

Results Immediate (2) ~1 week Immediate (2 ) ~2-3 weeks ~2-3 weeks
Type of Conditions Detected in the Baby Risk Assessment for:
Down syndrome, Trisomy 13
Trisomy 18. Some birth defects detectable at this gestation.
Risk Assessment for:
Down syndrome, Trisomy 18
ONTDs (3)
Serious birth defects
Soft markers for chromosome conditions.
Major chromosome conditions.
Genetic molecular testing if indicated.
Major chromosome conditions.
ONTDs (screen)
Detection Rate 85-90%

70% for Down syndrome,Trisomy 18

80% for ONTD

Majority of Major birth defects

90% for ONTDs 

> 99% for
chromosome conditions: (low risk for maternal cell contamination, confined placental mosacisim)
> 99% for chromosome
conditions
Further Testing Available

CVS or amniocentesis available for women identified at increased risk
(> 1:300 for Down syndrome; > 1: 150 for Trisomy 13 or 18).

18-20 week ultrasound to screen for birth defects.

Amniocentesis to detect chromosome conditions. Ultrasound to screen for ONTD and other serious birth defects. Amniocentesis to detect chromosome conditions.
or
Specific testing as indicated
18-20 week ultrasound to screen for birth defects 18-20 week ultrasound to screen for birth defects
Miscarriage Risk No added risk No added risk No added risk 1/100 (1% or less) 1/200 (0.5% or less)
Eligibility All pregnant women of any age All pregnant women of any age.
Not recommended if FTS has been performed.
All pregnant women of any age

Currently within the Calgary Health Region, CVS is limited and eligibility is determined on a case-by-case basis in consultation with MFM and/or Prenatal Genetics

Positive FTS or NT screen

Optional for women 35 years or older


1 Available through the Southern Alberta Centre for Maternal Fetal Medicine
(appointments: 289-9269 ).
Nuchal translucency screening is also a first trimester screen performed at 11-13 6/7 weeks. Detection rate for chromosome conditions is ~70-75%
2 When performed at the Southern Alberta Centre for Maternal Fetal Medicine.
3 ONTDs = Open Neural Tube Defects (eg. spina bifida).