SCREENING FOR MATERNAL CARRIER STATUS
FETAL CHROMOSOMAL/STRUCTURAL ABNORMALITIES
AND
RISK ASSESSMENT
Maternal carrier status of 12 of the most common inherited diseases is now available
to all patients through blood testing, performed either prior to conception or during
pregnancy. This test is done once per lifetime (rather than per pregnancy), because it
reflects the mother’s genetic makeup. Please inform your provider of any KNOWN
family history of genetic illnesses to ensure completeness. Fathers will be offered
testing in the setting of positive maternal screens to determine risk to current and
future pregnancies. The current standard panel screens for: Bloom syndrome,
Canavan disease, Cystic Fibrosis, Familial Dysautonomia, Fanconi Anemia (group C),
Fragile X syndrome, Gaucher disease, Glycogen Storage disease (type 1a),
Mucolipidosis (type IV), Niemann-Pick disease (types A&B), Spinal Muscular Atrophy
(also known as Muscular Dystrophy) and Tay-Sachs disease. An expanded panel is
available for patients with Ashkenazi Jewish heritage.
Non-invasive maternal blood screening for chromosomal (trisomy 13, 18 and 21) and
structural abnormalities (spina bifida) can detect approximately 81-87% of affected
pregnancies. Results are reported as a “risk ratio” that can be compared to your agerelated risk. Currently, two screens are available to ALL patients:
Nuchal translucency/first trimester screen (NTL): this screen can be performed
during a narrow time window (11-14 weeks of gestation) and usually must be
scheduled with the Maternal Fetal Medicine (MFM) specialists in Medford. This screen
measures the back of the fetal neck via ultrasound and uses blood obtained from the
mother’s fingertip to detect up to 87% of Down’s syndrome. This screen has a 5%
positive screen rate, meaning, 5% of pregnant patients will have a result suggesting an
increased risk of Down’s syndrome, even in the setting of a normal baby. An elevated
risk of Down’s (trisomy 21), Patau (trisomy 13) or Edwards (trisomy 18) syndrome will
result in a referral to an MFM for additional testing (see below).
Quad screen marker: this screen, performed using maternal blood drawn between 15
and 20 weeks, provides information about the risk of your baby being affected by
Down’s syndrome, trisomy 18 and open neural tube defect (spina bifida). By itself, the
screen detects approximately 81% of Down’s syndrome in low-risk mothers. This
screen also has a small risk of suggesting an abnormality in the setting of a normal
baby.
Alpha-fetoprotein by itself is used as a marker of open neural tube defect (also called
Spina Bifida, a congenital disorder caused by the incomplete closing of the embryonic
neural tube, allowing a portion of the spinal cord to protrude through the back bones).
AFP is obtained from maternal blood and can be used as an adjunct to NTL/first
trimester screening or on its own in the second trimester. It does NOT screen for
Down’s syndrome or other chromosomal abnormalities although it is used as an
independent predictor of pregnancy complications (see below).
Recently, a non-invasive (cannot be a cause of miscarriage) prenatal test was
developed to identify fetal aneuploidy (chromosomal abnormality) beginning at 10
weeks. This test uses cell free fetal DNA, collected from the maternal blood, to
identify abnormal amounts of fetal chromosomal material. This test can be used as a
follow-up for women with an abnormal first or second trimester screen prior to
invasive, confirmatory testing. It detects approximately 99% of trisomies. The test fails
to provide an “answer” in up to 5% of cases, usually because not enough fetal DNA is
recovered from the sample. All abnormal results are currently confirmed with invasive
testing, either chorionic villus sampling (CVS) or amniocentesis.
A small population of pregnant patients is currently eligible to “skip” non-invasive
screens and undergo cell free fetal DNA testing (depending on your insurance):
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Maternal age 35 years or older at delivery
Fetal ultrasonographic findings indicating an increased risk of aneuploidy
History of a prior pregnancy with a trisomy
Parental balanced robertsonian translocation (patient or father with
chromosomal abnormality)
The NTL/first trimester screen, Quad screen and AFP also have additional predictive
value beyond detecting chromosomal/structural abnormalities. They can also suggest
an increased risk of adverse pregnancy outcomes, including premature labor,
miscarriage, fetal death, pre-eclampsia and other related complications.
Depending on when you initiate care, you may be offered one or more of the
above-mentioned screens. Patients who are 35 or older at the time of delivery
OR who are at increased risk for genetic abnormalities due to history may be
offered early, invasive, definitive testing in the form of chorionic villus sampling
(CVS) or amniocentesis. Please be certain to discuss your preferences with your
provider.
CONSENT FOR
SCREENING FOR MATERNAL CARRIER STATUS
FETAL CHROMOSOMAL/STRUCTURAL ABNORMALITIES
AND
RISK ASSESSMENT
By my signature below I acknowledge that I have been provided all the information I
desire concerning screening for maternal genetic carrier status and fetal abnormalities
and that all of my questions have been answered to my satisfaction.
CHECK THE APPROPRIATE BOX BELOW. PLEASE DO NOT SIGN UNTIL YOU HAVE
READ AND UNDERSTOOD THIS INFORMATION:
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I consent to the performance of maternal carrier status screening for the 12
diseases listed above. I am aware that a negative result does not ensure an
unaffected fetus (due to the possibility of rare genetic variants). I also am aware
that a positive result will be managed with partner screening and possibly
invasive fetal testing.
I DECLINE maternal carrier status screening.
I have already had maternal carrier screening and have informed my provider of
the results.
I consent to the performance of NTL/first trimester screen (trisomy 13, 18, 21
and adverse pregnancy outcome). I am aware that this screen may require me
to travel out of town (Medford, Eugene) during a specific timeframe. I am also
aware that separate AFP will be offered between 15 and 20 weeks.
I consent to the performance of blood testing for the Quad marker (trisomy 18,
21, open neural tube defect and adverse pregnancy outcome).
I consent to the performance of blood testing for AFP only (open neural tube
defect and adverse pregnancy outcome).
I DECLINE ALL screening options.
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Signature
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Date