Maternal Screening

Sample for Maternal Screening

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

Precautions for Maternal Screening

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

Purpose of the test (Indications) for Maternal (prenatal) Screening:

1. These tests diagnose early pregnancy:
   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 the age of 35 years.
   1. Abnormal maternal alpha-fetoprotein.
   2. Abnormal HCG level.
   3. Abnormal unconjugated estriol level.
3. These are also indicated in women who have previous abnormal infants with birth defects.
4. To diagnose trisomy 21 (Down’s syndrome).
5. To diagnose trisomy 18.
6. Ethenic 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 previous pregnancy with a chromosomal abnormality.
11. In the case of inherited disorders like cystic fibrosis, sex-linked recessive disorders, and metabolic disorders.

Prenatal screening facts:

1. AFP protein is produced by the fetus.
   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 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. Down’s Syndrome chances increase with increasing age are:
   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 now, this screening is offered to pregnant women in the second trimester of pregnancy.
6. The screening tests are not diagnostic.
   1. In case of abnormality in screening tests, then confirmatory tests are advised.

Confirmatory tests are:

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

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

Screening tests available are:

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 done alone, AFP will detect only 30% of the cases with trisomy 21.
6. Detecting the abnormality earlier prepares the family for the coming abnormal baby, or they can make the decision to terminate the pregnancy.

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 the pituitary production of FSH.
4. It is secreted by the placenta during pregnancy.

Inhibin A:

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

Inhibin A in females:

1. It is undetectable before puberty.
2. There is a low level in the postmenopausal period due to absent follicular secretions.
3. During pregnancy produced by the placenta.
4. Inhibon A peaks at 8 to 10 weeks, then decline until 20 weeks. After that, it increases gradually till the term.

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

Definition of pregnancy-associated plasma protein-A:

• PAPP-A is a zinc-binding matrix metallo-proteinase produced by syncytiotrophoblastic cells.

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

A positive screening test is seen in the following conditions:

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

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