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Fetal Diagnostic Tests
Dual marker test
The double/dual marker test is conducted in the first trimester of pregnancy, which helps determine if the fetus has a risk of developing chromosomal abnormalities. It is a predictive test that is part of the first-trimester screening to find out if any abnormalities in the chromosomes can affect the baby’s growth. It is crucial to conduct this test in the first trimester to identify Down syndrome, Edward’s syndrome, and Patau syndrome in the baby. The dual-marker blood test only identifies the risk but does not confirm any abnormalities.
Triple test
The triple test is one of the screening tests that are used to identify pregnant women whose fetus is likely to be affected by trisomy 21 (Down syndrome) and who should then be offered a diagnostic test. It’s usually done between 16 and 18 weeks.
Quadruple test
The quadruple marker test, also known as the maternal serum test, is a blood test that provides useful information about the fetus. It helps estimate if a baby has an increased risk of having Down syndrome, trisomy 18, or neural tube defects. The quadruple marker test results help predict the risk of such birth defects.
NIPT (Non-Invasive Prenatal Testing)
NIPT is a safe, simple, and sensitive test to identify all chromosomal aneuploidies and sex chromosomal anomalies. On average, 10% of fetal DNA is present in maternal blood samples. The NIPT test uses cell-free DNA present in maternal blood, released from the placenta. These cells are shed into the mother’s bloodstream throughout the pregnancy. The DNA in placental cells is usually identical to fetal DNA. A highly sensitive NGS technique is used to analyze the chromosomal aneuploidies. NIPT is usually performed as early as 10 weeks or later in pregnancy to rule out gross chromosomal aneuploidies. The sensitivity of the test is 98–99%.
Limitations
- Mosaicism cannot be ruled out
- Minute deletions or duplications
- Single-gene disorders
Amniocentesis
It is an invasive prenatal test that is usually performed after 16 weeks of pregnancy. In this procedure, there is an aspiration of amniotic fluid from the amniotic cavity. A thin needle is used to withdraw amniotic fluid from the sac surrounding the fetus, which contains cells shed by the fetus. Cells contain the genetic material that is tested for chromosomal disorders or single-gene disorders. This procedure is performed trans-abdominally and under ultrasound guidance by a trained obstetrician. No anesthesia is required. It is a daycare procedure. This invasive procedure has a 1-2% miscarriage risk.
Pre-eclampsia screening
Pre-eclampsia is a condition that causes high blood pressure and other problems in pregnant women. The following tests are performed during the first trimester for risk assessment, to plan further monitoring during pregnancy, and to take preventive steps:
- A blood test for serum placental growth factor is a screening test at 1-14 weeks of pregnancy
- Blood pressure monitoring
- Urine for protein and kidney function
- To check liver function, serum creatinine, platelet counts, placental growth factor, uric acid and LDH
- Measuring maternal weight
- Ultrasound to assess uterine artery pulsatility index during first trimester NT scan
Fetal reduction
It is a procedure to reduce the number of fetuses in a multifetal (triplets/twins) pregnancy. This procedure is usually performed in the first trimester after the NT scan. The main purpose of fetal reduction is to reduce maternal risk. It is also performed on parental wishes. Multifetal pregnancies increase maternal risks for pre-eclampsia, GDM, hypertension, and post-partum hemorrhage; thus, fetal reduction improves pregnancy outcomes. By this procedure, triplet pregnancy can be reduced to twins (or) twins can be reduced to singleton pregnancy.