Management of pregnancy - VA/DoD Clinical Practice Guidelines ...

VA/DoD Clinical Practice Guideline
For Pregnancy Management
at least two values of MSAFP exceeding 2.5 MOM, when corrected for gestational age, should be referred to
advanced prenatal care follow-up.
Down syndrome (trisomy 21) occurs in 1/800 births, increasing in risk with advancing maternal age. Eighty percent
of babies with Down syndrome are born to women under 35 with no risk factors. Low MSAFP is associated with
increased risk for Down syndrome (Haddow et al., 1992). If risk for Down syndrome is calculated solely on age
versus AFP, detection increases from 25 to 37 percent. Pregnant women with fetuses affected by trisomy 21 tend to
have lower than average levels of MSAFP and unconjugated estriol with elevated levels of serum HCG, when
compared to women carrying euploid fetuses. Adding serum HCG and uncongugated estriol (“triple screen”)
increases detection to 56 to 75 percent without increasing false positivity (Smith-Bindman et al., 2001). Triple
screen also increases the antenatal detection rate for a variety of chromosome disorders, particularly sex
chromosome abnormalities (Kellner et al., 1995). Ultrasound to assess fetal age is indicated for all women with low
MSAFP or abnormal triple screen. It should be followed by amniocentesis for gestational age-adjusted persistent
abnormal values. The benefit of increased detection of chromosome abnormalities should be weighed against the
risk of fetal loss from amniocentesis.
Edward’s Syndrome (trisomy 18) occurs in approximately one in 5,000 live births and is associated with a high rate
of fetal death or early neonatal demise. Affected individuals surviving the neonatal period typically have profound
neurodevelopmental delay and are unlikely to survive beyond five years of age. Pregnant women with fetuses
affected by trisomy 18 tend to have lower than average levels of MSAFP, HCG, and unconjugated estriol.
Approximately 50 percent of fetuses with trisomy 18 can be detected with maternal serum analyte screening and
follow-up fetal karyotype analysis of screen-positive women.
Customary practice is to offer amniocentesis or chorionic villus sampling to all women age 35 or older at the time of
birth, and to women whose risk of Down syndrome by maternal serum analyte screening is equivalent to that of a
35-year-old woman. Data from randomized trials suggest the attributable risk of pregnancy loss due to
amniocentesis is less than 1:1500 when performed by experienced clinicians. Accordingly, ACOG has
recommended amniocentesis be available to women of all ages regardless of their a priori risk for carrying a fetus
with aneuploidy (ACOG, 2007).
For gravidas over 35, maternal serum analyte screening with subsequent confirmatory fetal karyotype analysis of
screen-positive women identify up to 89 percent of fetuses with Down syndrome, with a false positive rate of 25
percent. For pregnant women over 35 who are willing to accept a potentially false-negative screen, the quad screen
is a cost effective alternative to routine amniocentesis. This alternative practice could make more than 75 percent of
amniocenteses unnecessary, thereby also reducing amniocentesis-associated fetal losses (Haddow et al., 1994). The
complexity of the pre-screening and pre-testing counseling requires referral of high-risk women to a qualified
healthcare provider for counseling. Any pregnant women determined to have a fetus with a serious structural
abnormality or fetal aneuploidy should receive advanced prenatal care.
EVIDENCE TABLE
Recommendations Sources of Evidence LE QE SR
1 Offer multiple marker maternal serum
analyte screening to all pregnant
women at gestational ages between 15
and 20 weeks
ACOG, 2007
Haddow et al., 1992
Malone et al., 2005
II-1 Good B
2
Provide pre-test patient education and
counseling
Nadel et al., 1990
Dahl et al., 2006
Davey et al., 2005
II-2 Good B
3 Women at high-risk for fetal
aneuploidy (age =35 at delivery or
prior first child or fetus with
aneuploidy) require genetic counseling
Haddow et al.,1994 II-1 Good B
4 Screen-positive women require
targeted ultrasound examination for
Smith-Bindman et al., 2001
ACOG, 2007
II-1 Good B
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