Prenatal Diagnosis Flashcards
What is the definition of screening?
The identification, among apparently healthy individuals, of those who are sufficiently at risk of a specific disorder to justify a subsequent diagnostic test or procedure
What three criteria are needed for a screening test?
- Should identify women who are at increased risk, prior to having definitive diagnostic test
- Should be offered to all pregnant women who are considered to be only at population risk
- Should be beneficial to those who receive it
At what point should all mothers have amniocentesis?
When the risk of all diagnosable chromosomal abnormalities exceeds the reported risk of miscarriage, commonly around 35 years maternal age.
What is used for first trimester chromosomal abnormality screening? What would be found in abnormal?
PaPP-A - Pregnancy-associated plasma protein A - decreased in all chromosomal abnormalities
hCG - human chorionic gonadotropin - DECREASED in all chromosomal abnormalities, but INCREASED in Down’s syndrome
Nuchal translucency - thickness behind fetus’ neck - increased in all chromosomal abnormalities
What are the two tests for second trimester chromosomal abnormality screening?
- Triple test (MSAFP, hCG, estriol)
2. Quad test (MSAFP, hCG, estriol, inhibin)
What is MSAFP and when is it increased vs decreased?
Maternal Serum Alpha Feto Protein
Increased in Neural Tube Defects
Decreased in Down Syndrome
What are typical quad test findings for a Down syndrome baby?
MSAFP - low
hCG - high
estriol - low (fetal-placenta unit not well intact)
inhibin - high (produced in placenta)
What are the ultrasound findings for a baby with Down syndrome?
- Nuchal translucency is increased (skin of neck separation from underlying tissue)
- Nasal bone - reduced in length or absent
- AV cardiac defect
- Duodenal atresia - DOUBLE BUBBLE sign
What is the correct series of screening / diagnostic tests for Down syndrome?
- Run first trimester screening for PaPP-a, NT, hCG.
- If results indicate Down’s syndrome -> immediate diagnostic testing. If results are negative, proceed to second trimester screening (quad test)
- If second trimester screening is positive -> diagnostic testing
Make sure to test fetus if first semester screen was positive even if second semester was negative.
If MSAFP is high, which is amniocentesis checking for?
High acetylcholinesterase, which indicates a neural tube defect.
What does folic acid reduce the risk for?
Both orofacial clefting and neural tube defects
What are potential ultrasound findings for trisomy 18 (Edward)?
- Omphalocele - intestines not returning to body properly
- Rocker bottom feet
- Clenched hands
- Polyhydramnios
- Cystic hygroma
- CNS defects or neural tube defect
What are potential ultrasound findings for trisomy 13?
- Omphalocele as well
- Echogenic kidneys
- Polydactyly
- Cleft lip / palate
- Holoprosencephaly or microcephaly
What are potential ultrasound findings for Turner syndrome?
- Cystic hygroma
- Cardiac defects - coarctation of the aorta
- Horseshoe kidneys
- Hydrops - accumulation of fluid
How does ffDNA work? Is this considered diagnostic or screening?
Free fatal DNA - derived primarily from syncytiotrophoblasts in the placenta, fetal DNA appears as early as 5-7 weeks and is 5-25% of circulating DNA in mother’s serum. Next generation sequencing makes detect of chromosomal abnormalities 99% of the time and requires only a blood draw.
Considered a SCREENING test. Need to confirm definitively with appropriate diagnostic procedure