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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Information about the screening tests offered
– Detection rate
– False-positive rate
Risks and benefits associated with diagnostic procedures
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
– Stepwise sequential
– Contingent sequential
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 .
1st trimester: NT, PAPP-A + maternal age(90%-95%)
Risk based on maternal
age, 1st trimester + quad
1st trimester: NT, PAPP-A + maternal age
ABNORMAL SECOND-TRIMESTER MATERNAL SERUM MARKERS IN PREGNANCIES WITH A NORMAL KARYOTYPE
Unexplained Elevated Maternal Serum α-Fetoprotein(2.5MOM)
Several factors influence the maternal serum AFP level and are taken into consideration when calculating the AFP MoM:
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.
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.
Maternal Serum α-Fetoprotein
The combination of elevated MSAFP and hCG levels occurs
rarely but may have an overall pregnancy complication rate
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.
↑edinhibin A + ↑edhCG and/or AFP (>2.0MoM):
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%.