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Second-trimester maternal serum screening. Counseling for all patients. Information about the screening tests offered – Detection rate – False-positive rate – Advantages – Disadvantages – Limitations. Risks and benefits associated with diagnostic procedures. Goal for screening tests:.

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Second-trimester maternal serum screening

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Counseling for all patients

Information about the screening tests offered

– Detection rate

– False-positive rate

– Advantages

– Disadvantages

– Limitations

Risks and benefits associated with diagnostic procedures


Goal for screening tests:

  • High detection rates
  • Low false-positive rates
  • Provide patients with the diagnostic options
  • they might want to consider
  • Screening and invasive diagnostic testing should
  • be available to all women who present for prenatal care before 20 weeks of gestation regardless of maternal age.

First trimester screening with both NT and biochemical markers is an effective screening test for the general population, and is comparable to the 2nd trimester quadruple screen with the additional advantage of earlier

  • pregnancy terminations if desired.
  • Neural tube defect screening should be offered in the second trimester to women who elect only first trimester screening for aneuploidy
second trimester
Second Trimester

Quad Screen

  • 15-22 weeks gestation
  • AFP, hCG, uE3, inhibin A
  • 81% DR at a 5% positive screen rate
  • Good for women who don’t want 1st
  • trimester screening or who register for
  • care after first trimester

Used for detection of: n of:

  • ONTD
  • Down syndrome
  • trisomy 18
  • Smith-Lemli-Opitz syndrome


  • in maternal urine has been tested as a marker for Down syndrome
  • With the addition of extra markers, the potential benefit must be balanced against the cost.
screening tests that combine first and second trimester markers
Screening tests that combine first andsecond-trimester markers
  • Integrated
  • Sequential

– Stepwise sequential

– Contingent sequential


Integrated Screen(9O-96%)

Measurements during both trimesters are combined with maternal age to provide a

single estimate of a woman’s risk of

having a pregnancy affected by Down syndrome

1st trimester: PAPP-A and NT

2nd trimester: AFP, uE3, hCG, and inhibin-A

Offer when CVS is not available .


Sequential Screening Tests

  • Patient is informed of the first-trimester screening result
  • Allows patients the option to have CVS
  • – Stepwise Sequential Screening
  • – Contingent Sequential Screening
  • 88-94% DR at a 5% positive screen rate
stepwise sequential screen
Stepwise Sequential Screen

1st trimester: NT, PAPP-A + maternal age(90%-95%)

Risk Assessment



Quad screen


Risk based on maternal

age, 1st trimester + quad


contingent sequential screen 88 94
Contingent Sequential Screen(88-94%)

1st trimester: NT, PAPP-A + maternal age

  • screen positive → offer CVS(1%)
  • intermediate → offer quad screen(15%)
  • screen negative → no further testing(84%)


Unexplained Elevated Maternal Serum α-Fetoprotein(2.5MOM)

  • Ultrasound
  • 90% r/o spinal lesions
  • 100% r/o anencephaly
  • VWD reduced with normal scan
  • If MSAFP >4.0 MoM and NL U/S Offer invasive testing

ONTD screening

  • fetal growth restriction,
  • fetal death,
  • prematurity,
  • oligohydramnios,
  • abruptioplacentae, and preeclampsia.
  • no management protocol has been demonstrated to improve outcome in these cases.

Several factors influence the maternal serum AFP level and are taken into consideration when calculating the AFP MoM:

  • Maternal weight
  • Gestational age
  • Race or ethnicity
  • Diabetes
  • Multifetal gestation

Unexplained Elevated Human Chorionic GonadotropinLevels

unexplained elevated

hCG(>2.0 MoM) is associated with an increased risk for preeclampsia,pretermbirth, low birth weight, fetal demise, and possibly hypertension

Low Second-Trimester Maternal Serum Estriol

Low maternal serum unconjugatedestriol levels have been

linked to adverse pregnancy outcomes

Very low or absent estriollevels of 0.0 to 0.15 MoM suggest biochemical abnormalities of the fetus or placenta, including placental steroid

sulfatase deficiency,Smith-Lemli-Opitz syndrome, congenital adrenal hypoplasia,adrenocorticotropindeficiency,hypothalamiccorticotropindeficiency, and anencephaly.


Smith-Lemli-Opitz syndrome

occurs in approximately 1/60,000 pregnancies and is an autosomal recessive disorder

defect in 3β-hydroxysteroid-Δ7-reductase, altering cholesterol synthesis and resulting in low cholesterol levels and the accumulation of the cholesterol precursor 7-dehydrocholesterol in blood and amniotic fluid.

Smith-Lemli-Opitz syndrome is characterized by low birth weight, failure to thrive, and moderate to severe mental retardation.

It is associated with multiple structural anomalies,

including syndactyly of the second and third toes, microcephaly, ptosis, and a typical-appearing facies.

Undermasculinization of the genitalia, including complete sex reversal, can be

seen in male fetuses.


Elevated Human Chorionic Gonadotropin and

Maternal Serum α-Fetoprotein

The combination of elevated MSAFP and hCG levels occurs

rarely but may have an overall pregnancy complication rate

exceeding 50%.

preeclampsia, preterm birth, growth restriction, placental

abnormalities, and fetal death

Confined placental mosaicismfor chromosome 16 has been reported to be associated with extremely high levels of both analytes, as well as with similarly poor outcomes.


Abnormal Quad Screen Markers

↑edinhibin A + ↑edhCG and/or AFP (>2.0MoM):


  • Uterine artery Dopplers at @18-20 weeks
  • Close surveillance for IUGR and preeclampsia
  • Non-stress tests for cases with IUGR or preeclampsia

Down Syndrome Screening for Monozygotic Twins

  • Risk for aneuploidy is the same as for singleton
  • Average of the two NT measurements can be used to calculate the pregnancy risk
  • An enlarged NT and/or significantly discordant measurements between twins may be markers for adverse outcomes independent of aneuploidy risk
down syndrome screening for dizygotic twins 70 of twins
Down Syndrome Screening forDizygotic Twins (> 70% of twins)
  • Each fetus carries an independent risk for Down syndrome
  • Age-related risk for having 1 aneuploid fetus is higher than that of a woman with a singleton pregnancy
  • Individual NT measurements can be used to
  • calculate the fetus-specific risk
  • A maternal age of 31-33 years is the equivalent risk of a 35-year old woman with a singleton

Screening Tests in Twins

For twins, however, the value and accuracy of serum screening is much less certain because the contribution of an abnormal fetus will, on average, be brought closer to the normal mean by an unaffected co-twin.

This tends to decrease the overall screening sensitivity. Screening,

however, can be useful nonetheless.

At present, there is no standard agreement on the MSAFP elevation that warrants further evaluation in twins.

Some centers use a cutoff of 4.0 MoM, which would identify approximately

60% of fetuses with open spina bifida, but this has approximately an 8% incidence of false-positive results.

Other centers use a cutoff of 4.5 MoM, which has a sensitivity of approximately 50%.