prenatal diagnosis

Prenatal diagnosis

Dr.Maysarah M. AL-Badran
M.B.ch.B,C.A.B.O.G,F.I.C.M

Prenatal diagnosis

Identification of a disease before birth.
Usually preceded by screening test,women with risk factor identified during screening may undergo diagnostic test.

Screening test

Include:history:family hx,past obstetric hx
maternal biochemistry:Down syndrom
U/S:anomaly scan at 18-22wk

Diagnostic tests

High risk pregnancies
Invasive and non invasive
Invasive:amniocentesis,CVS, cordocentesis.
Risk of miscarrige



Non invasive prenatal diagnostic tests
US for structural abnormalities
Viral serology
free fetal DNA extracted from maternal blood to determine fetal blood group or the sex of fetus by PCR.
Fetal RNA from maternal to detect aneuploidy.

Pre-test counselling

Indication
The procedure
Risk,limitations
Management options:continue or terminate pregnancy

Amniocentesis

At or after 15 wk
Additional risk of miscarrige 1%
Earlier amniocentesis is more risk






Chorionic villus sampling
At or after 11 wk
Additional risk of miscarrige 2%
If performed before 10 wk:limb distruption and oromandibular hypoplasia
Transabdominal 0r transcervical
Confined placental mosaicim

Laboratory analysis

Full culture for karyotyping:7-10 days
Result for common aneuploidy(trisomy21,18,13) take 48 hours by Fluorescence in situ hybridization(FISH)or Polymerase chain reaction(PCR)
Tests for genetic disorders take varying time

Cordocentesis

Around 20 wk
Greater risk of miscarrige than amniocentesis and CVS(2-5%)
When fetal blood is needed as in alloimmune thrombocytopenia or when a rapid full culture for karyotype is needed

Screening for Down’s syndrom

Risk increases with age.
Quadriple test(14-20wk):B-hCG,α-fetoprotein,unconjugated estriol,inhibin A
Nuchal transulency:11-14 weeks
Combined test(11-14wk): NT,B-hCG,pregnancy associated plasma protein A(PAPP-A)

Structural abnormality

Neural tube defects:
Anencephaly&encephalocele can be detected on first trimester U/S
Spina bifida:’lemon’&’banana’sign
Can be prevented by folic acid 400Mg-----high risk 5mg

Congenital heart defects

Genetic,maternal DM,viral inf.,lithium
Screening by U/S &fetal echo.

Diagnosis of GIT Structural abnormalities

Gastroschisis: US detect 90% of cases,not associated with other abn. or chrom. abn.
Follow up is required—>risk of IUGR & oligohydramnios.
exomphalos:US detect 90% of cases,associated with chrom. Abn.& other structural abn.

Other methods of AN diagnosis

3D & 4D ultrasound
Fetal MRI:CNS abnormalities

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