Maternal Screening – Part 1 – Maternal Triple or Quadruple screening for Genetic abnormality
- These tests are done on the serum of the patient.
- A urine sample may also be needed.
- These tests are done during 14th to 20th weeks of gestation.
- Supplement these tests by ultrasound.
- Ultrasound helps to establish the exact age of the fetus.
- For confirmation:
- Chorionic villus samples may be taken in early pregnancy.
- Amniocentesis may be done if needed in mid-pregnancy.
- First-trimester screening relieves the anxiety of a mother earlier than doing the test in the 2nd trimester.
- The tripple screening test should be done between 15 to 20 weeks of gestation.
- 16 to 18 weeks are a more accurate test.
- These screening tests are just warning for fetal abnormality and these are not confirmatory.
Purpose of the test (Indications)
- These tests diagnose early pregnancy:
- A potential birth defect like neural tube defects or abdominal wall defect.
- Chromosomal or genetic abnormalities.
- These are indicated in women over the age of 35 years.
- These are also indicated in women who have previous abnormal infants with birth defects.
- To diagnose trisomy 21 (Down’s syndrome).
- To diagnose trisomy 18.
- AFP protein is produced by the fetus.
- HCG is the hormone produced from the placenta.
- Estriol is an estrogen hormone produced by the fetus and the placenta.
- With the help of these tests can diagnose:
- Neural tube defect like myelomeningocele or spina bifida.
- Abdominal wall defects like omphalocele or gastroschisis.
- The incidence of fetal abnormalities is related to the age of women.
- Down’s Syndrome chances increase with increasing age are:
- At the age of 25 years = 1:1300.
- At the age of 35 years = 1: 365.
- At the age of 45 years = 1:30.
- In the USA now this screening is offered to pregnant women in the second trimester of pregnancy.
- The screening tests are not diagnostic.
- In case of abnormality in screening tests then confirmatory tests are advised.
Confirmatory tests are:
- Chorionic villus sampling in the first trimester.
- Amniocentesis in the mid-pregnancy.
- In the USA mostly women are over the age of 35 years have chorionic villus sampling or amniocentesis.
Screening tests available are:
- Double screening test. This consists of two markers:
- Triple screening test. This consists of three markers:
- HCG (produced by the placenta).
- AFP (produced by the yolk sac and liver).
- Estriol (produced by the placenta).
- Quadruple screening test. This consists of four markers.
- Inhibin A.
- Triple screening is more popular because it can diagnose trisomy 21(Down’s syndrome) in 50% to 80% of the cases.
- AFP if done alone will detect only 30% of the case with trisomy 21.
- Detecting earlier the abnormality, prepare the family for the coming abnormal baby or they can make the decision to terminate the pregnancy.
- This is normally secreted by the granulosa cells of the ovary and inhibits FSH production from the pituitary gland.
- It is a glycoprotein of placental origin in pregnancy like HCG.
- It is important in the control of fetal growth.
- Its level is 2 times higher in trisomy 21 as compared to the normal pregnancy.
- Its level is lower in normal pregnancy as compared to women with spontaneous abortion.
Pregnancy-associated plasma protein-A (PAPP-A):
- This is produced by the placenta and the endometrium.
- Women with low PAPP-A at 8 to 14 weeks has the chances for:
- Intrauterine growth restriction.
- Trisomy 21.
- Premature labor.
- In trisomy 21 level is half of the normal level.
- 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:
- Trisomy 18.
- Trisomy 21.
- Neural tube defect.
- Abdominal wall defects.