Prenatal Assessment Flashcards
Key points about exomphalos?
Herniated abdominal contents in a sac at the base of the umbilical cord.
Elevated alpha feto protein but not as high as gastrochisis since the abdominal contents are covered.
May contain stomach, liver and spleen.
70-80% assoc with structural anomalies
1/3 rd of fetuses have chromosomal anomalies (so karyotyping is a must)
- mainly trisomy 18/21/13
- smaller exompthalos w/o liver usu assoc with chromosomal anomalies.
High assoc with other anomalies
-50% have associated cardiac anomalies
- 10% assoc with genetic syndromes (Beckwith Wiedmann)
Polyhydramnios
Prognosis dependent on presence other other anomalies - if no other, then good results post sx.
Features of gastrochisis?
Herniation of bowel that are not membrane covered and are exposed to the amniotic fluid.
Herniation is usually lateral (right) to the umbilical cord insertion.
High AFP
VERY low incidence of other anomalies
No increased incidence if chromosomal anomalies
Usu only small bowel herniates
Assoc with bowel ischaemia and atresia
Bowel dilation and thickening in later pregnancy
Oligohydramnios
FGR
Management:
Induce at 37 weeks at a type A institution with access to paediatric surgeons and neonatologist and NICU.
- no apparent benefit from delivery via LSCS
- surgical repair includes 1)reduction of bowel, 2) suturing of defect under local anaesthetic and 3) use of a silo to gradually return bowel to the abdomen or bowel resection in cases of bowel ischaemia
What are the causes of congenital anomalies?
1.Genetic/chromosomal anomalies
2. Consanguinuity (parents related by blood increases the risk of rare genetic anomalies)
3. Socioeconomic factors (reduces access to adequate nutrition and increased exposure to smoke, alcohol and drugs).
4. AMA (increased risk of Down’s and other anomalies)
5. Environmental (maternal exposure to certain medications, smoke, radiation)
6. Infections (Syphilis, rubella, zika)
What percentage of pregnancies have major structural anomalies?
2-3%
What percentage of neonatal deaths are accounted for by structural anomalies?
20-30%
What is the triple screen?
A second trimester biochemical screening test for chromosomal abnormalities, that measured uE3, hcg and AFP.
Sensitivity of 72% and false pos rate of 7%
DOES NOT meet criteria for an optimal screening test with 75% sensitivity and <3% false pos
What is the quadruple screen?
This is a second trimester screening test done at 15+0 to 20+0 weeks gestation, to assess for chromosomal abnormalities.
It involves uE3, hcg, afp and the addition of inhibin A, which (when compared to the triple test) increases the sensitivity to 75% and decreases the false positive rate to 5%.
This test is offered to
- women who present outside the first trimester and therefore cannot receive the T1 screen and
-to those in whom nuchal translucency was not obtained in the first trimester.
What is the combined screen?
The combined screen is a first trimester screen that does a combined assessment for trisomy 21, 18 and 13. This is performed at 11+0 to 13+6 weeks gestation and involves the use of ultrasound to measure nuchal translucency and biochemical tests (HCG and PAPP-A).
This test has a sensitivity of 90% and a false positive rate of 5%
What is noninvasive prenatal testing (NIPT)?
This is a screening test performed on cell free foetal DNA in maternal serum. It has a sensitivity of ~99% for aneuploidies with a false pos rate of <1%. It indicates if a fetus is at low or high risk for an anomaly.
Pos predict values:
80% - downs
50% - patau
40% - edwards
When to offer NIPT? If found to be high risk, what’s the next step?
After combined or quadruple screen comes back as high risk (1:150).
Can consider offering to very high risk pts initially (known parental abnormalities, prev child with anomaly).
If testing comes back as high risk, proceed to diagnostic testing.
What are the options for diagnostic prenatal Assessment?
Chorionic Villus Sampling
Done at 11 to 13+6
Procedure involves using a fine needle to take a small sample of placental tissue, transabdominally, under u/s guidance.
Amniocentesis
Is performed after 15+0 weeks (15-20 weeks ideally but can be done after)
Involves using a fine needle, passed transabdominally under u/s guidance, to collect ~20mls of amniotic fluid.
Both procedures are associated with a risk of:
Miscarriage - 1/100 or 1%
Chorioamnionitis - 1/1000 or 0.1%
Risks decrease to <0.5% if operator is very skilled/experienced.
Other risks include:
-Bloody amniotic fluid or inadequate volume of fluid (amniocentesis)
- fetal injury
- maternal bowel injury
- amniotic fluid leakage
- pain at procedure site
The samples can be sent for quantitative fluorescent PCR/QF-PCR or microarray. QF-PCR usu gives a rapid result w/in 3 days.
Anomaly detection rate for T1 u/s?
-dependent on whether pt is low or high risk for anomalies.
- low risk pts: 31-65%
- high risk: 54-74%
Limitations of T1 u/s?
- Limited detection of anomalies compared to T2 scan
- Anomalies may present different in T1 and T2 so risk of misdiagnosis
- No pathological confirmation of diagnosis
Key points of T1 CNS assessment?
- skull is ossified at 11 weeks
- butterfly appearance of choroid plexus
- cerebral hemispheres take up 2/3rd of head
What is the most common CNS anomaly?
Anencephaly - 1/ 1000 (0.1%)
Identified from 11 weeks onwards
What is an encephalocele?
Herniation of brain tissue through a defect in the skull. Appears as a cystic swelling through a defect in the cranial ring.
-75% of cases are occipital
- differential: cystic hygrometer
- LOOK for other abnormalities once diagnosed.
What is the significance of the nuchal translucency measurement?
If equal to or greater than 3.5mm there is an increased risk of fetal chromosomal abnormalities.
- increased NT is associated with structural anomalies and rare syndromes.
