Prenatal Assessment Flashcards

1
Q

Key points about exomphalos?

A

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.

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2
Q

Features of gastrochisis?

A

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

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3
Q

What are the causes of congenital anomalies?

A

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)

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4
Q

What percentage of pregnancies have major structural anomalies?

A

2-3%

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5
Q

What percentage of neonatal deaths are accounted for by structural anomalies?

A

20-30%

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6
Q

What is the triple screen?

A

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

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7
Q

What is the quadruple screen?

A

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.

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8
Q

What is the combined screen?

A

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%

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9
Q

What is noninvasive prenatal testing (NIPT)?

A

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

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10
Q

When to offer NIPT? If found to be high risk, what’s the next step?

A

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.

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11
Q

What are the options for diagnostic prenatal Assessment?

A

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.

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12
Q

Anomaly detection rate for T1 u/s?

A

-dependent on whether pt is low or high risk for anomalies.
- low risk pts: 31-65%
- high risk: 54-74%

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13
Q

Limitations of T1 u/s?

A
  1. Limited detection of anomalies compared to T2 scan
  2. Anomalies may present different in T1 and T2 so risk of misdiagnosis
  3. No pathological confirmation of diagnosis
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14
Q

Key points of T1 CNS assessment?

A
  • skull is ossified at 11 weeks
  • butterfly appearance of choroid plexus
  • cerebral hemispheres take up 2/3rd of head
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15
Q

What is the most common CNS anomaly?

A

Anencephaly - 1/ 1000 (0.1%)

Identified from 11 weeks onwards

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16
Q

What is an encephalocele?

A

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.

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17
Q

What is the significance of the nuchal translucency measurement?

A

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.
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18
Q

Optimal time for anomaly scan? Explain.

A

18 +0 -20+6

If anomaly scan is offered at 22 weeks, then a major anomaly is found that requires termination, the patient would have to undergo fetocide – offered to all women >21+6 undergoing a termination.

Repeat anomaly by 23+0 if difficult visualisation on initial scan.
- if and anomaly is suspected but the views are suboptimal — get a second opinion.

19
Q

What is placenta praevia?

A

Refers to a placenta that partially or wholly covers the internal cervical os. Diagnosed in the third trimester after formation of the lower uterine segment.

20
Q

What is a low-lying placenta?

A

Refers that a placental edge <20mm from the internal os on transabdominal or transvaginal ultrasound

21
Q

Should TVS be used for placenta praevia?

A

Yes
It is MORE accurate than transabdominal or transperineal and it is SAFE

22
Q

What is the significance of a short cervical length in a patient with placenta praevia?

A
  • patient may require emergency preterm delivery
  • increases risk of massive haemorrhage at LSCS
23
Q

Causes of fetal hydrops?

A
  1. Isoimmunization due to blood group antibodies
  2. Chromosomal and generic anomalies (trisomy 21, turner, other trisomies)
    3.Infection (cmv, provides, syphilis, coxackie)
  3. Fetal anaemia (alpha thalassemia, chronic feto-maternal haemorrhage)
  4. Cardiovascular (structural/tacharrhtymias causing increased central venous pressure)
  5. High cardiac output states (a-v malformations, teratomas)
  6. Pulmonary e.g. congenital cystic adenomatoid malformation (large lesions in chest rhythm press against heart can lead to heart failure and hydrops)
  7. Cystic hygroma
24
Q

What are the treatment options for hydrops?

A

The treatment depends on the underlying cause:
1. Parvovirus/isoimmunization- intrauterine transfusion; can have a good long term prognosis.

2.Syphilis - give the mother high dose penicillin and the hydrops will gradually resolve.

3.Coxsackie - may spontaneously resolve

4.CMV- assoc. With CNS damage therefore poor longterm prognosis

5.Antiarrythmic agents for arrhythmias.

  1. Termination if poor prognosis/longterm outlook OR abnormal karyotype OR other abnormalities are seen.
25
Q

What percentage of neonates with Downs syndrome have a structural anomaly?

A

55%

26
Q

What anomalies are assoc. with Down’s syndrome?

A

From head down (facial, cardiac, GI, urinary, limb defects).

Facial:
- brachycephaly
- flat back of head
- upstanting palpebral fissure
- epicanthic folds
- brushfield spots (white/grey/brown spots on periphery of iris due to aggregation of connective tissue)
- cataracts
- flattened nasal bridge
- lowset ears
- open mouth with protruding tongue
- abundant neck skin

Cardiac:
- atrial septal defects, ventricular septal defects, atrioventricular canal defects, ToF, pulmonary stenosis, PDA

GI:
duodenal atresia, exomphalos, hirschsprung’s disease

Limb:
Fifth finger clinodactyly
Single palmar/simian crease
Sandal gap

27
Q

Features of trisomy 18/Edward’s?

A

Associated with multiple anomalies.
Head to toe:
- early onset IUGR
- oligohydramnios
- Choroid plexus cyst
- CNS abnormalities
- prominent occipital
- small mouth & jaw
- dysplastic/malformed ears
- short neck
- overlapping fingers
- clenched fist
- cardiac/renal abnormalities
- 2 vessel umbilical cord
- rockerbottom feet
- flexed big toe, prominent heels
- skeletal abnormalities
-

28
Q

What is tetralogy of fallot?

A

VSD
Right ventricular hypertrophy
Pulmonary stenosis
High riding/overriding aorta

**Pulmonary stenosis causes right outflow obstruction

29
Q

T/F. Infants with ToF are cyanotic at birth? What scenarios causes cyanosis?

A

False, these babies are pink at birth.

  • Cyanosis occurs with crying or feeding, and it progresses over the first few weeks of life.
  • Cyanosis occus at REST in childhood and alleviated by the squatting position.
30
Q

What is the survival rate after sx for ToF?

A

95%

31
Q

What are Tet spells and how is it alleviated?

A

Tet spells are HYPERcyanotic spells caused by a quick drop in oxygen levels due to decreased blood flow to the lungs.

-They are alleviated by squatting.
-Squatting compresses and traps venous blood in the legs
- increasing peripheral vascular resistance in the aorta
- and DECREASING the right to left shunt across the VSD.
- this increases pulmonary flow

32
Q

What is Turner’s syndrome associated with?

A

-Increased nuchal translucency
- cystic hygroma
- hydrops

General exam:
- short stature
- Low hairline
- Webbed neck/folds of neck skin
- shield chest
- underdeveloped breasts
- numerous naevi/moles

Cardiac:
- atrial septal defects
- coarctation of the aorta

Genital:
Streak gonads
No uterus

Limbs:
Shortened 4th metacarpal
Small fingernails
Cubitus valgus (Elbow deformity)

33
Q

What is AFP? What is it used for?
When do levels peak?
Which conditions are assoc with elevated or decreased levels?

A

Alpha fetoprotein is produced by the fetal liver and measured in the maternal serum.
- it is mainly used to diagnose open neural tube defects.
- it reaches the liver by transfer via the placentavor amniotic fluid.
- it is produced between weeks 12 to 32, and peak between 16-18wks (testing is most sensitive).
- it is expressed a MoM (multiples of the normal median) for gestational age.

  • Elevated AFP - multiple gestation, FGR, fetal demise, anencephaly, open neural tube defects (spina bifida), anterior abd wall defects (exomphalos), congenital nephrosis
  • Decreased AFP: Down’s, Edward’s, maternal obesity, insulin dependent diabetes
34
Q

Sensitivity of AFP? Compare to u/s.

A

Sensitivity of:
79% for open spina bifida
88% for anencephaly

High resolution ultrasound is more sensitive, hence AFP is superseded by u/s dor diagnosis and screening for neural tube defects.

AFP still has a role in aneuploidy screening in the quadriple (and triple) screening.

35
Q

List the quad screen results for:
Downs
Edwards
Patau
Turner’s
Smith-Lemlie-Opitz syndrome

A

21- high hcg and inhibin a, low afp and ue3
18- all low
13- very low ue3; afp & hcg either very high/low
XO- low Afp and ue3; high hcg
SML (autosomal recessive w/ mental restriction) - low hcg & afp; ue3 very low/undetectable

36
Q

Patient known to have sickle cell/HbSS and her partner has HbSC. Justify your next step.

A

Offer chorionic villus sampling and genetic testing to the couple but subsequent counseling.

37
Q

Bilateral choroid plexus cysts are noted on ultrasound but no other fetal abnormality. Justify next step.

A

Reassure the patient as choroid plexus is a soft marker that is seen in up to 3% (0.2-3%) of normal pregnancies.

It is also seen in patau’s trisomy 13, but other features would also be noted on ultrasound.

38
Q

A short femur <3rd centile is noted on the anomaly scan report. Justify your next step?

A

Serial growth assessments in the third trimester.

-A short femur in the absence of other deformities is usually constitutional.
- It could also represent intrauterine growth restriction.

39
Q

At what gestational age is a history indicated cerclage performed and what are the indications for one?

A

GA 11-14 in asymptomatic women

Indications:
3 prior preterm deliveries/T2 losses

40
Q

When should chorionicity for multiple gestations be determined

A

CRL 45 - 84mm
11+0 - 13+6 wks

41
Q

When is the quadruple test done?

A

14+2 - 20+0 weeks

? From 15 weeks

42
Q

Optimal time to perform ultrasonographic measurement of cervical length with a h/o 2 prior pregnancy?

A

14-20 wks (check)

43
Q

What is the preferred GA to recan a woman with:
1. A low-lying placenta
2. Suspected asymptomatic placenta praevia
3. Suspected placenta accreta

A
  1. 36 weeks [32 wks GTG 27a]
  2. 32 weeks
  3. 32 weeks