Maternal Screening

What sample is needed for Maternal Screening?

1. These tests are done on the patient’s serum.
2. A urine sample may also be needed.
3. These tests are done during the 14th to 20th weeks of gestation.
4. Supplement these tests with ultrasound.
   1. Ultrasound helps to establish the exact age of the fetus.
5. For confirmation:
6. Chorionic villus samples may be taken in early pregnancy.
7. Amniocentesis may be done if needed in mid-pregnancy.
8. First-trimester screening relieves a mother’s anxiety earlier than doing the test in the 2nd trimester.

What are the precautions for Maternal Screening?

1. The tripple screening test should be done between 15 and 20 weeks of gestation.
2. A 16- to 18-week test is more accurate.
3. These screening tests are just a warning of fetal abnormality and are not confirmatory.

What are the Indications for Maternal (prenatal) Screening?

1. These tests diagnose early pregnancy abnormalities like:
   1. A potential birth defect like neural tube defects or abdominal wall defects.
   2. Chromosomal or genetic abnormalities.
2. These are indicated in women over 35 years of age.
   1. Abnormal maternal alpha-fetoprotein.
   2. Abnormal HCG level.
   3. Abnormal unconjugated estriol level.
3. These are also indicated in women who have had previous abnormal infants with birth defects.
4. To diagnose trisomy 21 (Down’s syndrome).
5. To diagnose trisomy 18.
6. Ethnic risk factors like sickle cell anemia, Tay-Sachs disease, α- and β-thalassemia.
7. In the case of rubella, toxoplasmosis, or CMV infection.
8. If the mother suffers from diabetes mellitus and phenylketonuria.
9. If pregnant women are exposed to teratogenic material like radiation, chemotherapy, alcohol, anticonvulsants, and lithium.
10. In the case of a previous pregnancy with a chromosomal abnormality.
11. In the case of inherited disorders like cystic fibrosis, sex-linked recessive disorders, and metabolic disorders.

What is the significance of  Prenatal screening?

1. The fetus produces AFP protein.
   1. HCG is the hormone produced by the placenta.
   2. Estriol is an estrogen hormone produced by the fetus and the placenta.
2. With the help of these tests, one can diagnose:
   1. Neural tube defects like myelomeningocele or spina bifida.
   2. Abdominal wall defects like omphalocele or gastroschisis.
3. The incidence of fetal abnormalities is related to the age of women.
4. The chances of Down’s syndrome increase with increasing age:
   1. At the age of 25 years = 1:1300.
   2. At the age of 35 years = 1: 365.
   3. At the age of 45 years = 1:30.
5. In the USA, this screening is now offered to pregnant women in the second trimester.
6. The screening tests are not diagnostic.
   1. In case of abnormality in screening tests, confirmatory tests are advised.

What are the confirmatory tests for finding fetal abnormalities?

1. Chorionic villus sampling in the first trimester.
2. Amniocentesis in mid-pregnancy.

• In the USA, most women over the age of 35 years have chorionic villus sampling or amniocentesis.

What screening tests are available to find fetal abnormalities?

1. Double screening test: This consists of two markers:
   1. HCG.
   2. AFP

2. Triple screening test: This consists of three markers:
   1. HCG (produced by the placenta).
   2. AFP (produced by the yolk sac and liver).
   3. Estriol (produced by the placenta).
3. Quadruple screening test:  This consists of four markers.
   1. HCG.
   2. AFP.
   3. Estriol.
   4. Inhibin A.

4. Triple screening is more popular because it can diagnose trisomy 21 (Down’s syndrome) in 50% to 80% of the cases.
5. If performed alone, AFP will detect only 30% of cases of trisomy 21.
6. Detecting the abnormality earlier prepares the family for the coming abnormal baby, or they can decide to terminate the pregnancy.

How would you define Inhibin A and B?

Definition of Inhibin A and B:

1. It is a polypeptide hormone and belongs to the transforming growth factor family.
2. Inhibin is secreted by granulosa cells of the ovary and the Sertoli cells of the testes.
3. It inhibits pituitary FSH production.
4. The placenta secretes it during pregnancy.

Inhibin A:

How will you define Inhibin A?

1. The corpus luteum produces inhibin A.
2. This is normally secreted by the ovary granulosa cells and inhibits FSH production from the pituitary gland.
3. It is a placental glycoprotein produced during pregnancy, like HCG.
4. It is important in the control of fetal growth.
5. Its level is 2 times higher in trisomy 21 than in a normal pregnancy.
6. Its level is lower in normal pregnancy as compared to women with spontaneous abortion.

What is the role of Inhibin A in females?

1. It is undetectable before puberty.
2. There is a low level during the postmenopausal period due to the absence of follicular secretions.
3. During pregnancy, it is produced by the placenta.
4. Inhibin A peaks at 8 to 10 weeks and then declines until 20 weeks. After that, it increases gradually until the term.

Inhibin B:

How will you define inhibin B?

1. Inhibin B is mainly produced by the granulosa cells.
2. It is associated with ovarian follicular activity.

What is the function of inhibin B?

1. Its main function is to suppress FSH.
2. It is a marker of Sertoli cell function.
3. It has a role in spermatogenesis.

How will you compare inhibin A and Inhibin B?

How will you summarize Inhibin A and B?

1. Inhibin A   = Pregnancy and part of quad screening.
2. Inhibin B = Sertoli cells and spermatogenesis.
3. Both inhibit secretion of FSH from the anterior pituitary gland.

Pregnancy-associated plasma protein-A (PAPP-A):

How will you define pregnancy-associated plasma protein-A?

1. PAPP-A is a zinc-binding matrix metallo-proteinase produced by syncytiotrophoblastic cells.
2. This is produced by the placenta and the endometrium.
3. Women with low PAPP-A at 8 to 14 weeks have the chance of:
   1. Intrauterine growth restriction.
   2. Trisomy 21.
   3. Premature labor.
   4. Pre-eclampsia.
   5. Stillbirth.
4. In trisomy 21, the level is half of the normal level.
5. A low level in the third trimester is associated with severe fetal abnormalities, fetal death, and intrauterine growth restriction.

Where would you see a positive screening test?

1. Trisomy 18.
2. Trisomy 21.
3. Neural tube defect.
4. Abdominal wall defects.

Questions and answers:

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