Antenatal Diagnosis of Congenital Abnormalities Flashcards
What process does cfDNA use to detect abnormalities?
Massive parallel sequencing of foetal DNA present in maternal plasma. Alignment of sequencing reads to human genome sequence and determination of relative chromosome representation
When is cfDNA available from?
From 9 weeks gestation
What is the turnaround time for cfDNA?
~2 weeks (all samples sent overseas)
How does cfDNA compare to other screening strategies for T18, 21?
Superior sensitivity and lower false positive rates than other screening strategies
What must be done prior to cfDNA?
Dating / viability scan
What is the purpose of the 12 week scna?
Diagnosis of foetal defects
Which structural abnormalities may be visualised at 12 week US?
- Anencephaly
- Alobar holoprosencephaly
- Exomphalos
- Gastroschisis
- Megacystitis
- Absent hand / foot
- Polydactyly
- Diaphragmatic hernia
- lethal skeletal dysplasia
- major cong heart defect
- facial cleft / open spina bifid (rarely detectable)
Why is ductus venosus assessed?
- Positive association between chromosomal abnormalities and abnormal DV flow in first trimester.
- +ve association with cardiac anomalies
What are the trisomy 18 US anomalies?
- strawberry shaped head
- choroid plexus cyst
- absent corpus callous
- ventriculomegaly
- facial cleft
- nuchal oedema
- cardiac defects
- oesophageal atresia
- exomphalos
- renal defects
- myelomeningocele
- talipes / rocker bottom feet
- overlapping fingers
- growth restriction
What are the trisomy 13 US anomalies?
- holoprocenphaly
- anopthalmia / micropthalmia
- abnormal nose
- facial clefts
- cardiac abnormalities
- omphalocele
- renal abnormalities
- postaxial polydactyly
- myelomeningocele
Triploidy US findings?
- partial mole
- growth restriction
- mild ventriculomegaly
- micrognathia
- cardiac abnormalities
- omphalocele
- small abdo circumference
- myelomeningocele
- 3rd-4th fingers syndactyly
- “Hitch Hiker” toe deformity
What are the types congenital heart defects relating to conotruncual abnormalities?
- transposition of the great arteries
- truncus arteriosus
- double outlet of the right ventricle
- tetralogy of Fallot
What are the congenital heart defects relating to conotruncual abnormalities?
- heterogenous group of defects involving ventricles and great arteries
- 20-30% cardiac anomalies
- leading causes of symptomatic cyanotic heart disease
- CFx within h/d
- good prognosis with prompt treat hence antenatal diagnosis important
What other abnormalities is congenital diaphragmatic hernia associated with?
- lung hypoplasia
- pulmonary HTN
Incidence congenital diagphragmatic hernia?
1:4000
What causes diagphragmatic hernia?
- failed obliteration of pleuro peritoneal canal
- herniation of abdominal organs into the chest
which other conditions is diaphragmatic hernia associated with?
Chromosomal anomalies: -trisomy 18 -trisomy 13 -mosaic tetrasomy 12p (Pallister-Killian) Other anomalies: -Iniencephaly -Fryn -De Lange -Beckwith Wiedemann
What are the prognostic factors in isolated CDH?
- liver position (2/3 have some liver up)
- lung to head ratio
- polyhydramnios
- mediastinal shift
What is ventriculomegaly?
- mean 6-7mm stable across 2nd and 3rd trimesters
- sign but not diagnosis
- severe = hydrocephaly
- mild >10-
What is congenital hydrocephaly?
-heterogenous group with multiple causes (genetic, infectious, teratogenic, neoplastic)
What are the infectious causes of congenital hydrocephaly?
- syphilis
- toxoplasmosis
- CMV
- mumps
- influenza
What is the process of congenital hydrocephaly?
- Disruption of ependymal lining
- oedema of the WM
- proliferation of astrocytes and fibrosis
- thinning of the cortex
- macrocrania
What are the risks associated with mild ventriculomegaly?
Increased risk of extracranial anomalies, other CNS anomalies, aneuploidy, congenital infections, perinatal death, abnormal intellectual development
When does the callosum develop?
Between 10 - 25 weeks
What are the obstetric indications for MRI?
- foetal abnormality assessment
- High risk pregnancies for cerebral ischaemia (multiple pregnancy, TTTS)
- Foetal surgery assessment
- placenta accreta, suspected percreta
- maternal illness
- post mortem MRI
What are the indications for foetal brain MRI?
No definitive, US best early / MRI best late. MRI if suspected abnormality on US
- Mlformation
- posterior fossa assessment
- supratentorial anomaly
- ventriculomegaly
- high risk foetus (genetic, TTTS, severe anaemia, maternal infection)
What is the “structure” of scans throughout pregnancy (timing and purpose etc)?
Scan structure
5-10 weeks: number of foetus
11-14: screening for common / severe physical anomalies, T21
14-20: repeat scans, bleeding
20-22: morphology scan (congenital anomalies)
>24w: foetal growth and welbeing
Why are does the detection of chromosomal abnormalities decrease with gestational age?
Many lethal abnormalities die in utero hence higher rates earlier in pregnancy
When should definite testing be offered in DS screening?
If final result is higher than 1:300 offer definite testing (risk of miscarriage 1:400 from amnio hence DS risk same / similar as change of harm)
What is the DS screening program structure?
Women have blood test at 10 weeks; results at 12 week scan
Combine age, NT, gestational age and add blood markers for 1st test (bHCG, PAPPA)
What are the blood markers in DS screening?
- bHCG usually double in DS
- PAPPA; pregnancy associated protein A; low in DS
