a presentation describing the two common prenatal diagnosis techniques; amniocentesis and chorionic villus sampling.

1. PRENATAL DIAGNOSIS TECHNIQUES
- STEVE RYAN

2. WHAT IS PRENATAL DIAGNOSIS?
 Prenatal Diagnosis refers to the diagnosis of the unborn baby
while in the foetal stage.
 It is used to see if the developing baby has any genetic
disorders like down syndrome (trisomy 21), split spine (spina
bifida) etc.,
 It is generally done for pregnant women who are older than 35
years, since they have an increased risk of having a baby with a
chromosomal abnormality.
 It is also done for couples who have had a child with genetic
abnormalities, or for couples who are known to be carriers of a
genetic disorder.

3. TYPES OF PRENATAL DIAGNOSIS
 Prenatal Diagnosis Techniques are generally classified into two
types, Invasive and Non-Invasive, based on the intrusion of the
foetal space.

4. Invasive Prenatal Testing (IPT)
 Invasive Prenatal Testing is a method of testing by which test
samples are directly collected from the foetal space.
 These samples generally includes the amniotic fluid, the
placental tissue, foetal blood, foetal tissue etc.,
 The two main methods of IPT are;
AMNIOCENTESIS
CHORIONIC VILLUS SAMPLING (CVT)

5. AMNIOCENTESIS
 What is Amniocentesis?
 Amniocentesis (or) Amniotic Fluid Test, is a type of Invasive
Prenatal Testing (IPT), which is primarily used for prenatal
diagnosis of chromosomal abnormalities, foetal infections, as
well as sex determination of the child.
 In this method, the Amniotic fluid of the foetus is collected from
the uterus either for testing or to drain the excess of
accumulated amniotic fluid (polyhydramnios).
 Doctors Jens Bang and Allen Northeved from Denmark were the
first to report amniocentesis done with the guide of an
ultrasound in 1972
 The cost for amniocentesis in India varies from Rs. 7000 to Rs.
18000

6. What is the amniotic fluid?
 The amniotic fluid is a clear, slightly yellowish liquid that surrounds
the foetus during pregnancy. It is present in the amniotic sac. It
protects the fetus from injury and temp change.
 It contains amniotic membrane cells and fetus skin cells which are
then cultured to detect any chromosomal anomaly in the fetus
 The foetus swallows this fluid to develop the
gastrointestinal tract.

7. How it’s done:
 First, the woman is made to lie on an exam table, with their
abdomen exposed.
 Then, the doctor will use an ultrasound transducer to
determine the baby’s exact location in the uterus.
 Next, the doctor will clean the abdomen of the woman with
an antiseptic.
 Guided by ultrasound, the doctor will insert a thin, hollow
needle through the abdominal wall and into the uterus

8.  A small amount of amniotic fluid (15-20ml) will be withdrawn
into a syringe, and the needle will be removed.
 The amount of fluid withdrawn depends on the week of
pregnancy. It is replaced by injecting a saline fluid.
 The woman might feel cramping when the needle enters the
uterus.

9.  After the procedure is over, the heartbeat of the foetus is
monitored for some time using ultrasound, to make sure the
foetus is unharmed.
 The woman can resume normal activity after the procedure.
However, the woman is advised to avoid major physical
activities for a few days.
 Meanwhile, the sample of amniotic fluid will be analysed in a
lab, and the results might be available within few days, or
upto four weeks, depending on the type of result.

10. When it’s done:
 Amniocentesis is usually done between 14th to 20th week of
pregnancy, but it is ideally done between 15th to 17th week.
 If performed too early (10-14 weeks), the uterus won’t be very
accessible and the foetal cells might be too low for sampling. It
also increases the risk of spontaneous abortion and rupture of
foetal membranes. It may also cause club foot(talipes
equinovarus).
 If performed too late, the foetal cells might be keratinised and
unfit for sampling.

11. Why is it performed?
 Doctors don’t generally perform amniocentesis for pregnant
woman as a regular check up.
 A doctor may recommend amniocentesis if:
• The woman will be 35 or older at the time of delivery.
• There is a family history of congenital disabilities or genetic
disorders.
• Prenatal screening tests have given abnormal results.
• The woman has a child with a congenital disability or genetic
condition.

12. Uses of amniocentesis:
 Amniocentesis is mainly used to detect genetic anomalies like Down
syndrome(trisomy -21), Edwards syndrome(trisomy-18), Tay-Sachs
disease, split spine condition(spina bifida) etc., with 99% accuracy.
 It can be used to diagnose haemophilia (improper blood clotting)
 Paternity testing: Amniocentesis can collect DNA from the fetus
that can then be compared to DNA from the potential father.
 If the baby has certain health issues, like anemia, the doctor may
be able to treat these during the pregnancy.
 Used to treat polyhydramnios.
 It is also used to determine the sex of the child, but that test is
restricted in India due to an increasing case of female foeticide.

13. Complications:
 If the mother’s blood type is rhesus (RhD) negative but the baby's
blood type is RhD positive, it's possible for sensitization to occur
during amniocentesis. Which may cause erythroblastosis fetalis
(rhesus disease).
 The fetus might get injured by the needle if not done properly.
 Amniocentesis performed on the beginning of the second
trimester carries a slight risk of miscarriage.
 amniocentesis might trigger a uterine infection, but it’s very rare.
Spontaneous abortions (miscarriages) = < 1%
Contamination of the amniotic fluid by stem cells = 0.15 – 0.11%.
Loss of amniotic fluid = 1 – 2 %.
Blood loss, with scanty “spotting”: very rare.

14. Advantages and Disadvantages:
Advantages:
 Relatively cheap procedure
 Can detect abnormalities with 99% accuracy
 Chances of abortion is very low (0.5 – 1%)
 Enables a couple to abort a genetically abnormal child, for
family planning.
Disadvantages:
 Early testing can cause higher risk of miscarriage (5%)
 If the mother has infections like HIV, it may pass on to the baby
due to this procedure.

15. Amniocentesis and Female Foeticide:
 One of the major disadvantages of amniocentesis is
misusing this to identify the gender of the fetus, and if it
is a female, the fetus is aborted.
 To prevent this misuse, the government of India passed on
the Preconception and Pre-Natal Diagnostic Techniques
Act in 1994, which imposes strict restrictions and
regulations on the hospitals performing this procedure
 If the doctor performing this procedure reveals the gender
of the baby to the parents, the doctor may face
imprisonment and have their license revoked.

16. Chorionic Villus Sampling (CVS)
 Also known as Chorion Biopsy, it is a form of prenatal
diagnosis done to determine chromosomal or genetic
disorders in the fetus. It entails sampling of the chorionic
villus and testing it for chromosomal abnormalities.
 It's only offered if there's a high chance your baby could
have a genetic or chromosomal condition, or due to
suspicious findings in antenatal scanning.
 Chorionic villus sampling was first performed by Italian
biologist Giuseppe Simoni in 1983.
 The cost for CVS in India varies from Rs.10,000 to
Rs.15,000

17. What is the Chorionic Villi?
 The chorionic villi are tiny projections of placental tissue that
look like fingers and contain the same genetic material as the
fetus.
 It facilitates the supply of oxygen and nutrients to the embryo.
 Trophoblast cells make up the Chorionic Villi.

18. How it’s done:
 First, the baby’s gestational age and position of the placenta
is verified via ultrasound.
 The doctor will use the ultrasound image as a guide and take
the tissue sample from the placenta.
The tissue sample can be taken by two methods:
 Transabdominal CVS
 Transcervical CVS

19. Transabdominal approach
 After cleansing the abdomen with an antiseptic, the doctor will insert a
long, thin needle through the abdominal wall, into the uterus of the
mother and to the edge of the placenta.
 The mother might notice a stinging sensation when the needle enters the
skin, and she might feel cramping when the needle enters the uterus.
 The tissue sample from the placenta will be withdrawn into a syringe, and
the needle will be removed.

20. Transcervical approach
 In this approach, after cleansing the vagina and the cervix
with an antiseptic, the doctor will open the vagina with a
speculum and insert a thin, hollow tube through the cervix
 When the catheter reaches the placenta, gentle suction will
be used to remove a small tissue sample

21.  After the procedure is over, the woman might experience a
small amount of vaginal bleeding immediately after the
procedure.
 The fetus’ heart rate and the mother’s vital signs will be
reassessed.
 If the mother’s blood is Rh negative, she will be given Rh(D)
immune globulin. This is a specially developed blood
product that can prevent an Rh negative mother's antibodies
from reacting to Rh positive fetal cells.
 The patient is monitored for 24 hours.

22. When it is done:
 CVS is usually performed between the 10th – 12th week of
pregnancy, but it can be performed at the 15th week too, if
necessary.
 If CVS is done before the 10th week, there is a higher risk of
miscarriage (transcervical approach has a higher risk than
transabdominal approach)
 Early CVS can also lead to abnormalities of the foetal limbs,
Micrognathia (deformity of the lower jaw) and Microglossia
(under developed tongue)
 The most ideal period for this procedure is the 11th – 12th
week of pregnancy.

23. Why is it performed?
 Physicians will recommend CVS if there is a high risk of the
baby being born with genetic abnormalities, or if previous
screenings had some abnormal sightings.
 If non invasive prenatal diagnosis detected some
abnormalities, this test is done to verify the abnormalities.
Other reasons include:
 Previously affected child or a family history of a genetic
disease, chromosomal abnormalities, or metabolic disorder
 Maternal age over 35 years by the pregnancy due date

24. Complications:
Chorionic villus sampling carries various risks, including:
 Miscarriage. The risk of miscarriage after chorionic villus
sampling is estimated to be 1% percent.
 Rh sensitization.
 Infection. Very rarely, chorionic villus sampling might
trigger a uterine infection.
 Some older studies suggested that chorionic villus
sampling might cause defects in a baby's fingers or toes.
However, the risk appears to be a concern only if the
procedure is done before week 10 of pregnancy.

25. Uses:
 Chorionic villi provide excellent material to conduct DNA
molecular studies and enzymatic determinations.
 CVS can help identify such chromosomal problems as
Down syndrome or other genetic diseases such as cystic
fibrosis, Tay-Sachs disease, and sickle cell anemia.
 It can also find the gender of the child.
 Earlier testing helps the mother to make easier family
planning decisions.

26. Advantages
 The main advantage of CVS is that it can be performed
much earlier than amniocentesis, thereby enabling the
parents to make a decision more easily.
 It has a high accuracy rate of 98%
Disadvantages
 neural tube defects, such as spina bifida, can't be
detected.
 difficult cytogenetic analysis and the possibility of
contamination with maternal cells might show inaccuracy.
 Infections of the mother can get passed on to the fetus
(HIV).

27. Difference b/w Amniocentesis and CVS
Amniocentesis Chorionic Biopsy
1. Done between 15 – 17 weeks of pregnancy Done between 11 – 14 weeks of
pregnancy
2. Amniotic fluid is taken as a sample Chorionic Villus is sampled
3. Has lesser risk of miscarriage Has more risk compared to amniocentesis
4. Provides information on neural tube
defects like spina bifilda
Does not provide information on neural
tube defects.
5. It can also be done to treat
polyhydramnious.
It is done solely for the purpose of testing
and diagnosis.
6. Does not require the patient to be
admitted
Requires the patient to be admitted for
at least 24 hours.

28. Thank You!