Serum screening Flashcards
Maternal AFP
Assess the risk for fetal open neural tube defect
Can also be used to assess for the risk of aneuploidy, such as Down syndrome or trisomy 18
Most common causes of abnormal serum screening
Wrong dates and multiple gestations
Appropriate window for serum screening
16-20 weeks
Components of certain LMP
Patient sure of date of LMP
Regular menses
LMP was normal
No spotting or bleeding after LMP
First trimester screening
10-13 weeks gestation
PAPP-A and beta-HCG and/or assessing US for nuchal translucency to assess for Down and trisomy 18
Trisomy screen
msAFP, hCG, inhibin-A, and unconjugated estriol
Performed at 15-21 weeks gestation
Elevated msAFP (value)
> 2.0 to 2.5 MOM
Why is msAFP elevated in neural tube defects?
AFP is synthesized by fetal yolk sac and then later the fetal GI tract and liver
Opening in the fetus not covered by skin –> AFP increases
Elevated msAFP causes
Underestimation of gestational age Multiple gestations Neural tube defects Abdominal wall defects Cystic hygroma Fetal skin defects Sacrococcygealteratoma Decreased maternal weight Oligohydramnios
Decreased msAFP causes
Overestimation of gestational age Chromosomal trisomies Molar pregnancy Fetal death Increased maternal weight
Trisomy 21 serum analysis
Increased inhibin-A and beta-hCG
Decreased AFP, uE3, PAPP-A
Trisomy 18 serum analysis
Decreased beta-hCG, AFP, uE3, PAPP-A
Trisomy 13 serum analysis
Decreased beta-hCG and PAPP-A
Down syndrome US
Thickened nuchal fold, shorter femur length, ***
