Prenatal screening Flashcards Preview

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Flashcards in Prenatal screening Deck (51):
1

Commonest cause of term stillbirth (5)

Preeclampsia
Abruption
Unexplained
Infection including GBS
Congenital abnormality

2

Common fetal anomalies

Hypospadias
Down syndrome
Neural tube
Hernia

3

Detection of anomalies dependant on

Primary or tertiary service
Type of anomaly- higher for NTD vs CHD
Gestation
High or low risk

4

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

5

Which aneuploidy has same risk regardless of age

Triploidy

6

Current down syndrome screening- Combined first trimester screen

Maternal age
Fetal nuchal translucency
Nasal bone
Maternal serum bHCG
PAPP-A at 11 - 13 +6

7

When is the CFTS done

11-13 +6 weeks

8

If CFTS cannot be done, what is an alternative

Second trimester biochemistry at 15-20 weeks

9

Is the morphology scan at 20 weeks a screening test for aneuploidy

No

10

What is the false positive rate for prenatal screening for Downs

5%

11

When is amniocentesis performed

15-18 weeks

12

When is chorionic villous sampling performed

10-12 weeks

13

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

14

When does NT increase normally

With increasing CRL

15

Does NT increase with increasing T21 risk or reduce

Increases

16

How does risk of T21 change with increasing gestation

Decreases with increasing gestation

17

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

18

Fetal loss rate with CVS

1-2%

19

How long do results take with CVS

2 weeks

20

Advantage and disadvantage of CVS

Quicker, can do suction currette if aneuploidy
1-2% fetal loss

21

How long for amnio results

3 weeks

22

Major disadvantage to amniocentesis

If termination- requires induction

23

Management of abnormal results in AC or CVS

Wait and see
Termination

24

Termination of pregnancy

suction, GA, prostaglandin 8-10 hours prior (Misoprostol)
16-20 weeks->induce with PG

25

What is cell free fetal DNA (MPS)

Detectable from 7 weeks
Fetal DNA in maternal plasma derived from placenta via apoptosis

26

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

27

What does NIPT test for

T21, T13, T18 45X

28

Compare NIPT to Amniocentesis

Does not pick up all xsome abnormalities
Still requires definitive testing if abnormal result

29

What is the routine second trimester test and what is the timing

Morphology scan
18-20 weeks

30

Limitations of morphology scan

Maternal obesity
Abdominal/pelvic scars
Fetal lie, crowding, oligo/anhydramnios, polyhydramnios

31

Survey scan

Pelvic, uterine masses
Fetal number
Fetal viability
Fetal lie
Amniotic fluid

32

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

33

What are the biometric measurements (5 + others)

Biparietal
Head circumference
Adbominal circumference
Femur length
Humerus length
Lateral ventricles, CM, NF, nasal bone, cervical length

34

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

35

Anatomic assessment of head and neck

Skull
Cerebellum
Cisterna magnum
Lateral ventricles
Falx
Cavum septu pellucidi
Cerebral hemispheres

36

Anatomic assessment of face

Profile
nasal bone
Orbits
Nose/lips

37

Anatomic assessment of chest

4 chamber heart view with outflow tracts
Lungs

38

Anatomic assessment abdomen

Stomach
Kidneys
Bladder
Liver
Diaphragm
Abdo wall/cord insertion
3 vessel cord

39

Other first trimester US markers

Nasal bone
FHR
TR
Ductus venosous
Frontomaxillary facial

40

Purpose of markers

Reduce the false positiv rate but maintain the sensitivity

41

When are the other markers useful

In the intermediate group 1 in 50 to 1 in 1000 for T21

42

What is US fetal tachyC and what is it a marker for

>175
Trisomy 13
improves detection by 5%

43

How does FHR help distinguish T13 and 18

T13 faster, T18 slower

44

What is TR a marker for

T21

45

What percent of T21 have normal morphology scan

50%

46

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

47

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

48

Isolated soft markers to follow up

Multiple
Thickened NF
Hypoplastic NB
AP renal pelvis >4mm
Echogenic bowel > bone
Mid trimester short long bones

49

Second trimester anomalies requiring tertiary

Ventriculomegaly
Cardiac
Omphalocele
Gastroschisis
Renal tract abnormal
NTD

50

Risks of amniocentesis

Pain, cramping
Vaginal spotting
Amniotic fluid leakage
Amnionitis
1 in 200 fetal loss

51

Complications of CVS

Preterm
PROM
Fetal injury