Prenatal screening Flashcards
Commonest cause of term stillbirth (5)
Preeclampsia Abruption Unexplained Infection including GBS Congenital abnormality
Common fetal anomalies
Hypospadias
Down syndrome
Neural tube
Hernia
Detection of anomalies dependant on
Primary or tertiary service
Type of anomaly- higher for NTD vs CHD
Gestation
High or low risk
Maternal age and risk of down syndrome at birth, age 20, 30, 35, 40, 44
1 in 1500 1 in 900 1 in 360 1 in 100 1 in 50
Which aneuploidy has same risk regardless of age
Triploidy
Current down syndrome screening- Combined first trimester screen
Maternal age Fetal nuchal translucency Nasal bone Maternal serum bHCG PAPP-A at 11 - 13 +6
When is the CFTS done
11-13 +6 weeks
If CFTS cannot be done, what is an alternative
Second trimester biochemistry at 15-20 weeks
Is the morphology scan at 20 weeks a screening test for aneuploidy
No
What is the false positive rate for prenatal screening for Downs
5%
When is amniocentesis performed
15-18 weeks
When is chorionic villous sampling performed
10-12 weeks
Steps to calculate trisomy 21 risk
Step 1: Maternal age Step 2: Background aneuploidy risk, increases with previous aneuploidy Step 3: NT Step 4: gestation Step 5: free bHCG and PAPP-A
When does NT increase normally
With increasing CRL
Does NT increase with increasing T21 risk or reduce
Increases
How does risk of T21 change with increasing gestation
Decreases with increasing gestation
If lost/has baby with aneuploidy, recommendations for next pregnancy
Some delay before trying 6-12 months
Screening test - risk now increased
Definitive testing
CVS at 12 weeks
Fetal loss rate with CVS
1-2%
How long do results take with CVS
2 weeks
Advantage and disadvantage of CVS
Quicker, can do suction currette if aneuploidy
1-2% fetal loss
How long for amnio results
3 weeks
Major disadvantage to amniocentesis
If termination- requires induction
Management of abnormal results in AC or CVS
Wait and see
Termination
Termination of pregnancy
suction, GA, prostaglandin 8-10 hours prior (Misoprostol)
16-20 weeks->induce with PG
What is cell free fetal DNA (MPS)
Detectable from 7 weeks
Fetal DNA in maternal plasma derived from placenta via apoptosis
What does massive parallel sequencing do
Counts the relative proportion of DNA fragments from different chromosomes, therefore if trisomic the relative amount of DNA from that chromosome will be more
What does NIPT test for
T21, T13, T18 45X
Compare NIPT to Amniocentesis
Does not pick up all xsome abnormalities
Still requires definitive testing if abnormal result
What is the routine second trimester test and what is the timing
Morphology scan
18-20 weeks
Limitations of morphology scan
Maternal obesity
Abdominal/pelvic scars
Fetal lie, crowding, oligo/anhydramnios, polyhydramnios
Survey scan
Pelvic, uterine masses Fetal number Fetal viability Fetal lie Amniotic fluid
What should be documented with regards to the placenta
Position Relation to the os Ant/post/lateral Clear of os, low lying, placenta previa Report distance from lower edge of placenta to internal os Myometrium behind placenta Cord insertion into placenta
What are the biometric measurements (5 + others)
Biparietal Head circumference Adbominal circumference Femur length Humerus length Lateral ventricles, CM, NF, nasal bone, cervical length
Rules of thumb for biometric measurements
Measure the BPD, FL and HL twice, if not within 2 mm, measure a third time
Measure the HC and AC twice, if not within 5mm, measure a third time
Anatomic assessment of head and neck
Skull Cerebellum Cisterna magnum Lateral ventricles Falx Cavum septu pellucidi Cerebral hemispheres
Anatomic assessment of face
Profile
nasal bone
Orbits
Nose/lips
Anatomic assessment of chest
4 chamber heart view with outflow tracts
Lungs
Anatomic assessment abdomen
Stomach Kidneys Bladder Liver Diaphragm Abdo wall/cord insertion 3 vessel cord
Other first trimester US markers
Nasal bone FHR TR Ductus venosous Frontomaxillary facial
Purpose of markers
Reduce the false positiv rate but maintain the sensitivity
When are the other markers useful
In the intermediate group 1 in 50 to 1 in 1000 for T21
What is US fetal tachyC and what is it a marker for
> 175
Trisomy 13
improves detection by 5%
How does FHR help distinguish T13 and 18
T13 faster, T18 slower
What is TR a marker for
T21
What percent of T21 have normal morphology scan
50%
Soft markers on morphology scan for Downs
Pyelectasis >4mm Hypoplasia of 5th metacarpal Absent or hypoplastic nasal bone Hyperechoic bowel Nuchal fold >6mm Echogenic cardiac focus
Isolated soft marker not requiring further scan and why
Echogenic intracardiac focus
Choroid plexus cysts
Cystic space >5mm in choroid
1-3% in normal population
Isolated soft markers to follow up
Multiple Thickened NF Hypoplastic NB AP renal pelvis >4mm Echogenic bowel > bone Mid trimester short long bones
Second trimester anomalies requiring tertiary
Ventriculomegaly Cardiac Omphalocele Gastroschisis Renal tract abnormal NTD
Risks of amniocentesis
Pain, cramping Vaginal spotting Amniotic fluid leakage Amnionitis 1 in 200 fetal loss
Complications of CVS
Preterm
PROM
Fetal injury
