12_Prenatal_diagnotic_tests.pdf

2. Prenatal Diagnostic Tests

3. Invasive Procedures
Cordocentesis

4. PREREQUISITES
• Detailed counseling should precede
(risks/benefits/technical aspects of tests)
• Indications :
✓ Increased risk for fetal chromosomal abnormality
✓ Hereditary, genetic cases
✓Perinatal infections.
✓Maternal Request- Extreme maternal anxiety inspite of
extensive counselling

5. CHECKLIST !
• The Rhesus status of the mother.
• Strict Asepsis
• Ultrasound- Viability , number of fetus ,placenta location,
Gestational age, Amniotic fluid should be checked before
and after.
• Universal maternal screening for HIV/HBV/HCV-- is not
recommended, limited to those with high viral load.(2)
• Antibiotic prophylaxis before -- not recommended.(3)
3.Mujezinovic F et al, Technique modifications for reducing the risks from amniocentesis or
chorionic villus sampling. Cochrane Database Syst Rev 2012; 8: CD008678.

6. Aspect Amniocentesis CVS FBS
Definition Transabdominal aspiration of
amniotic fluid from the uterine
cavity
Withdrawal of trophoblastic cells
from the placenta.
2 Indications
Fetal Hematological
assessment
Chromosomal
Mosaicism
Timing At or beyond 15weeks
<15weeks –
✓ Risks of high fetal loss
(7.6% vs 5.9%)
✓ Talipes,
(1.3% vs 0.1%)
✓ post procedure amniotic
fluid leakage
(3.5% vs 1.7%) (4)
after 10 + 0 gestational
weeks
< 10 weeks
✓ increase risk of fetal
loss
✓ Limb reduction
✓ oromandibular
hypoplasia
After 18 + 0 weeks
Technique Explained .
Laboratory
aspects
Failure of amniocyte culture
1%
Blood stained AF
Late Gestational age of
>28wks, increases risk (5)
Failure of the
cytotrophoblastic culture –
Placental cell mosaicism is
seen in 1% of
procedures.(10)

7. WHY !
Early Amniocentesis :
This may be due to the presence of the extraembryonic celom in the first
trimester or the reduced amount of amniotic fluid in the amniotic cavity. (1)
CVS < 10weeks:
• The limbs and mandible seem to be more susceptible to vascular
disruption before 10 weeks (1)

8. Aspect Amniocentesis CVS FBS
Complications
a)Fetal loss
b)Amniotic fluid
leakage
0.1-1% in comparision with
controls, with recent studies
being closer to 0.1% (1)
Varies between 1-2%.
✓ Increased risk of leakage
after amnio in those upto
24weeks.
✓ Spontaneous closure
occurs
✓ Low perinatal loss
compared to PVPROM
Observational Trials
showed ranging from 0.2 to
2% .
Transabdominal CVS vs
Amniocenetsis -
No difference(56)
Transcervical CVS vs
Amniocenteses- Pregnancy
loss
Extremely rare
Risk of fetal loss
between 1% and
2%(1)

9. Aspect Amniocentesis CVS FBS
c)Choriomamnionitis
d)Maternal
complications
e) Vaginal bleeding
Low
Due to bowel
perforation, Sepsis
nil 10% of cases

10. Amniocentesis CVS FBS
Increased risk
of
complications
✓ Structural anomalies
✓ 3/more punctures
✓ Blood stained AF
✓ Others-
NON CONSISTENT
✓ Mullerian anomalies,
vaginal
bleeding/Infection,
Retrochorionic
hematoma, BMI>40,
Multiparity >3, BOH
If more than two
punctures are necessary-
----to delay the
procedure by 24 hours
3,22
✓ African‐American
maternal race,
✓ At least two
aspirations/needle
insertions,
✓ heavy bleeding
during CVS,
✓ maternal age < 25
years
✓ Gestational age at
CVS < 10 wks
✓ Low PAAP A
✓ Persistent post CVS
bradycardia
✓ Structural
defects
(including
hydrops),
✓ IUGR
✓ possibly,
gestational age
< 24 weeks

11. AMNIOCENTESIS
Transabdominal:
• Asepsis – Painting and draping of site , cleaning of probe, sterile gel.
• A 20–22-G needle can be used, avoiding transplacental entry.
• Firm entry
• Once the needle has reached the amniotic cavity,
the inner stylet is removed ,the first 2 mL of fluid should be discarded(6) to avoid
maternal cell contamination,
15–30 mL fluid (depending on the indication) is aspirated.
• EVIDENCE
RCT comparing 20-G and 22-G needles, show similar rates of Intraterine bleeding and fetal
loss.(7)

12. CHORIONIC VILLOUS SAMPLING
• Transabdominal approach.
• Local anesthesia may be applied .
• A single needle of 17–20 G can be used.
• Once the needle has reached the target within the placenta, between one
and 10 back‐and‐forth movements are performed, while the vacuum is
maintained and samples are aspirated.
• Transcervical approach.
• Biopsy forceps are inserted transvaginally through the cervical canal to the
trophoblastic area, or a catheter with plastic or metal stylet under syringe
aspiration may be used.
• The amount of villi obtained in the sample must be checked visually.
• A minimum amount of 5 mg villi in each sample is required to achieve a
valid result (1)

13. CORDOCENTESIS/FBS
Approach:
1.Umbilical vein for FBS.
2.Puncture of the intrahepatic portion of the vein via
the fetal liver.
Difficult access of cord
Failed sampling of cord
Advantages:
Absent cord complications
Less risk of Fetal blood loss, FMH
Certainity of origin of blood

14. FBS Technique
A 20–22‐G needle is introduced transabdominally under USG
guidance and Inserted into the umbilical vein.
Anterior placenta--- umbilical vein at placental insertion
Posterior placenta--- a free loop of the cord or the
intra‐abdominal portion of the umbilical vein is sampled (1).
• Once the needle appears to have reached the target, flushing
with saline may be used to confirm its correct position
followed by aspiration.
• Avoid the umbilical arteries.
• Origin of the blood should be confirmed to assess the mean
corpuscular cell volume, or using a rapid acidification test (i.e.
Kleihauer Betke or Apt test).

15. POST PROCEDURE
▪ A detailed report regarding the procedure must be provided.
▪ Limiting physical activity for 12–24 h is optional as there is no evidence of
clinical benefit.
▪ Administration of progesterone or tocolytic drugs (i.e. terbutaline) has not
been demonstrated to yield a clear benefit in terms of relevant clinical
outcome (10)
• Cochrane Database Syst Rev 2012; 8: CD008678