Prenatal diagnosis

Question 1

What are the first trimester screening tests?

Answer 1

Combined Test
1- HCG
2- PAPPA
3- Nuchal translucency: measured when CRL is 45-84mm

at 10 - 14 weeks

Question 2

What are the anomalies that can be suspected using the first trimester combined test?

Answer 2

• Trisomy 21 -> high HCG + low PAPPA
• Trisomy 18 -> low HCG + low PAPPA

Question 3

What are the second trimester screening tests?

Answer 3

Quad screening at 15-20 weeks
1- maternal serum alpha fetoprotein
2- HCG
3- Inhibin
4- Unconjugated estriol

Question 4

What are the soft markers that indicate increased risk of having aneuploidies?

Answer 4

First trimester
- increased Nuchal translucency

Second trimester
- D-echogenic bowel
- B-echogenic intracardiac focus
- short femur
- absent fetal nasal bone

Question 5

What is the relation of first trimester screening with maternal age?

Answer 5

• mothers < 35 years -> trisomy 21 detection rate is 6 - 75%
• mother > 35 years -> detection rate 90%

Question 6

What are the indicators of trisomy 21 in combined first & second trimester screening tests?

Answer 6

• MSAFP decreased
• HCG increased
• PAPPA decreased
• unconjugated estriol decreased
• inhibin increased
• Nuchal translucency increased

Question 7

What are the indicators of trisomy 18 in combined first & second trimester screening tests?

Answer 7

• MSAFP decreased
• HCG decreased
• PAPPA decreased
• unconjugated estriol decreased

Question 8

What are the causes of a high MSAFP?

Answer 8

1- underestimated gestational age
2- multifetal gestation
3- fetal death
4- neural-tube defect
5- esophageal or intestinal obstruction
6- liver necrosis
7- renal abnormalities: polycystic kidneys, renal agenesis, congenital nephrosis, urinary tract obstruction
8- placental abruption
9- oligohydramnios
10- preeclampsia
11- fetal-growth restriction

Question 9

What is the best way to have the highest detection rates?

Answer 9

integrated first & second trimester tests

Question 10

How is cell free fetal DNA preformed?

Answer 10

DNA fragments from apoptotic trophoblasts
- after 10 weeks
- 99% detection rate
- noninvasive

Question 11

What screening tests should be done in the preconception period?

Answer 11

• Haemoglobinopathies -> sickle cell disease, thalassamia
• Spinal muscular dystrophy
• Cystic fibrosis
• used for preimplantation diagnosis
• ethnic based carrier screening

Question 12

What are the invasive diagnostic tests?

Answer 12

Chorionic villus sampling
- First trimester -> 10-13 weeks
- karyotyping
- transcervical or transabdominal
- risk of miscarriage & limb reduction defects

Amniocentesis
- Second trimester -> 15-20 weeks
- transabdominal
- risk of pregnancy loss

GIVE ANTI-D in Rh -ive moms AFTER BOTH

Question 13

What are the indications for amniocentesis?

Answer 13

• diagnosis of aneuploidies
• congenital infection
• red cell alloimmunization

Question 14

What are the indications for cordocentesis?

Answer 14

sampling of fetal blood for
- fetal blood transfusion in RH
- allo immunization
- platelet allo immunization
- karyotyping