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Obstetrics and Gynaecology > Prenatal screening > Flashcards

Prenatal screening Flashcards

1
Q

Commonest cause of term stillbirth (5)

A 
Preeclampsia
Abruption
Unexplained
Infection including GBS
Congenital abnormality
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2
Q

Common fetal anomalies

A

Hypospadias
Down syndrome
Neural tube
Hernia

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3
Q

Detection of anomalies dependant on

A

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

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4
Q

Maternal age and risk of down syndrome at birth, age 20, 30, 35, 40, 44

A 
1 in 1500
1 in 900
1 in 360
1 in 100
1 in 50
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5
Q

Which aneuploidy has same risk regardless of age

A

Triploidy

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6
Q

Current down syndrome screening- Combined first trimester screen

A 
Maternal age
Fetal nuchal translucency
Nasal bone
Maternal serum bHCG
PAPP-A at 11 - 13 +6
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7
Q

When is the CFTS done

A

11-13 +6 weeks

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8
Q

If CFTS cannot be done, what is an alternative

A

Second trimester biochemistry at 15-20 weeks

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9
Q

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

A

No

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10
Q

What is the false positive rate for prenatal screening for Downs

A

5%

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11
Q

When is amniocentesis performed

A

15-18 weeks

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12
Q

When is chorionic villous sampling performed

A

10-12 weeks

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13
Q

Steps to calculate trisomy 21 risk

A 
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
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14
Q

When does NT increase normally

A

With increasing CRL

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15
Q

Does NT increase with increasing T21 risk or reduce

A

Increases

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16
Q

How does risk of T21 change with increasing gestation

A

Decreases with increasing gestation

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17
Q

If lost/has baby with aneuploidy, recommendations for next pregnancy

A

Some delay before trying 6-12 months
Screening test - risk now increased
Definitive testing
CVS at 12 weeks

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18
Q

Fetal loss rate with CVS

A

1-2%

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19
Q

How long do results take with CVS

A

2 weeks

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20
Q

Advantage and disadvantage of CVS

A

Quicker, can do suction currette if aneuploidy

1-2% fetal loss

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21
Q

How long for amnio results

A

3 weeks

22
Q

Major disadvantage to amniocentesis

A

If termination- requires induction

23
Q

Management of abnormal results in AC or CVS

A

Wait and see

Termination

24
Q

Termination of pregnancy

A

suction, GA, prostaglandin 8-10 hours prior (Misoprostol)

16-20 weeks->induce with PG

25
Q

What is cell free fetal DNA (MPS)

A

Detectable from 7 weeks

Fetal DNA in maternal plasma derived from placenta via apoptosis

26
Q

What does massive parallel sequencing do

A

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
Q

What does NIPT test for

A

T21, T13, T18 45X

28
Q

Compare NIPT to Amniocentesis

A

Does not pick up all xsome abnormalities

Still requires definitive testing if abnormal result

29
Q

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

A

Morphology scan

18-20 weeks

30
Q

Limitations of morphology scan

A

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

31
Q

Survey scan

A 
Pelvic, uterine masses
Fetal number
Fetal viability
Fetal lie
Amniotic fluid
32
Q

What should be documented with regards to the placenta

A 
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
Q

What are the biometric measurements (5 + others)

A 
Biparietal
Head circumference
Adbominal circumference
Femur length
Humerus length
Lateral ventricles, CM, NF, nasal bone, cervical length
34
Q

Rules of thumb for biometric measurements

A

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
Q

Anatomic assessment of head and neck

A 
Skull
Cerebellum
Cisterna magnum
Lateral ventricles
Falx
Cavum septu pellucidi
Cerebral hemispheres
36
Q

Anatomic assessment of face

A

Profile
nasal bone
Orbits
Nose/lips

37
Q

Anatomic assessment of chest

A

4 chamber heart view with outflow tracts

Lungs

38
Q

Anatomic assessment abdomen

A 
Stomach
Kidneys
Bladder
Liver
Diaphragm
Abdo wall/cord insertion
3 vessel cord
39
Q

Other first trimester US markers

A 
Nasal bone
FHR
TR
Ductus venosous
Frontomaxillary facial
40
Q

Purpose of markers

A

Reduce the false positiv rate but maintain the sensitivity

41
Q

When are the other markers useful

A

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

42
Q

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

A

> 175
Trisomy 13
improves detection by 5%

43
Q

How does FHR help distinguish T13 and 18

A

T13 faster, T18 slower

44
Q

What is TR a marker for

A

T21

45
Q

What percent of T21 have normal morphology scan

A

50%

46
Q

Soft markers on morphology scan for Downs

A 
Pyelectasis >4mm
Hypoplasia of 5th metacarpal
Absent or hypoplastic nasal bone
Hyperechoic bowel
Nuchal fold >6mm
Echogenic cardiac focus
47
Q

Isolated soft marker not requiring further scan and why

A

Echogenic intracardiac focus
Choroid plexus cysts
Cystic space >5mm in choroid
1-3% in normal population

48
Q

Isolated soft markers to follow up

A 
Multiple
Thickened NF
Hypoplastic NB
AP renal pelvis >4mm
Echogenic bowel > bone
Mid trimester short long bones
49
Q

Second trimester anomalies requiring tertiary

A 
Ventriculomegaly
Cardiac
Omphalocele
Gastroschisis
Renal tract abnormal
NTD
50
Q

Risks of amniocentesis

A 
Pain, cramping
Vaginal spotting
Amniotic fluid leakage
Amnionitis
1 in 200 fetal loss
51
Q

Complications of CVS

A

Preterm
PROM
Fetal injury

Obstetrics and Gynaecology (45 decks)

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