T2 L11: Prenatal screening Flashcards
What is the scan at 10-14 weeks for?
- To check for viability
- Accurate dating
- Multiple pregnancy
- Diagnosis of major structural abnormalities like spina bifida, anencephaly, exomphalos, bladder outflow obstruction
- Screening for chromosomal conditions
2-3% women will have miscarried by this point
Why is accurate dating important?
It’s needed for screening and reduces induction of labour at the wrong time
In which type of multiple pregnancy is there a membrane between the babies?
In dichorionic twins (from different eggs)
In monochorionic twins there is no membrane because the babies split from the same egg
What is trisomy 21?
Down’s syndrome
It’s the most common type of chromosomal condition
What is trisomy 18?
Edward’s syndrome
What is trisomy 13?
Patau’s syndrome
It’s the least common type of chromosomal condition
What are the symptoms of Edwards syndrome?
Microcephaly (small and abnormally shaped head)
Micrognathia (abnormally small jaw and mouth)
Long, overlapping fingers and underdeveloped fingernails.
Scrunched fists.
Low-set ears.
Arched spine and abnormally shaped chest.
Crossed legs.
Umbilical hernia
The babies don’t live long
What are the symptoms of Patau’s syndrome?
cleft lip and palate.
an abnormally small eye or eyes (microphthalmia)
absence of 1 or both eyes (anophthalmia)
reduced distance between the eyes (hypotelorism)
problems with the development of the nasal passages
The babies don’t live long
What does first trimester combines screening include?
It takes into account maternal age, results from a nuchal translucency scan, and PAPP-A and beta-hCG blood markers to show the chance of a baby having a chromosomal condition
How does a Nuchal translucency (NT) scan show chromosomal abnormalities possibility?
If there is extra fluid, it can indicate an abnormality
What levels of beta-hCG and PAPP-A can predict downs syndrome?
high free beta-hCG and low PAPP-A
What are some influencing factors for combined screening which can obscure the results?
Maternal age Gestational age Ethnicity Smoking IVF Multiple pregnancies Maternal diabetes Past history of chromosomal abnormalities Fetal sex
When is a second trimester quadruple screening test offered?
- Unable to measure nuchal translucency Eg. due to fetal position
- Pregnancy is too advanced
Only screens for Down’s syndrome
What factors does a second trimester quadruple screen measure?
- Gestational age
- Maternal age
- Smoking
- Weight
- Ethnicity
- 4 maternal biochemical markers: UE3 unconjugated estriol (placental hormone), AFP alpha fetoprotein (protein from fetus), Inhibin A placental hormone, and beta-human chorionic gonadotrophin (BHCG placental hormone)
Which screening test is the best for chromosomal abnormalities?
The combined because it has a higher detection rate than the quadruple screen
What are the 2 diagnostic invasive tests for chromosomal abnormalities?
Chorionic Villus Sampling 11+ weeks
Amniocentesis 15+ weeks
Around 0.5%-1% risk of miscarriage (higher in twins)
What does non-invasive prenatal screening involve?
It tests the fetal DNA in the mothers blood
When is non-invasive prenatal screening (NIPT) offered?
- After a higher chance result from the combined or quadruple test
- To singleton and twin pregnancies only
- Up to 21 weeks and 6 days of pregnancy to allow time to abort is needed
When is non-invasive prenatal screening not offered?
- Maternal cancer because there will be free fetal DNA from tumour
- Possibility of donor DNA Eg. after blood transfusion, organ transplant, stem cell therapy
- Vanished twin
- Known maternal trisomy 21/balanced translocation/mosaicism of T13/18/21
What are the advantages of NIPT screening?
- High detection rate, low screen positive rates
- Reduced invasive diagnostic techniques
What are the disadvantages of NIPT screening?
- Not diagnostic (false positives/false negatives)
- Not suitable for everybody
- Expensive
- Results can only be confirmed with invasive tests
Which 11 conditions are screened for at the mid-trimester scan?
Anencephaly Open spina bifida Cleft lip Diaphragmatic hernia Gastroschisis Exomphalos Transposition of the great arteries Atrioventricular septal defect Tetralogy of fallot Hypoplastic left heart syndrome Bilateral renal agenesis Lethal skeletal dysplasia T13 and T18
