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A historical and practical review of first trimester aneuploidy screening

There have been tremendous advancements over the past three decades in prenatal screening for aneuploidy and we have changed our practice from screening by maternal age alone to ‘combined’ first trimester screening and circulating cell-free fetal DNA. We currently use the nuchal translucency and biochemical markers of free β-hCG and PAPP-A to determine the risk of fetal aneuploidy. The primary goal is to identify higher risk women for fetal aneuploidy early in pregnancy and give them the option to pursue invasive testing in a timely manner if desired.

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 First Trimester Screening, Nuchal Translucency and NIPT

First trimester screening (FTS), nuchal translucency (NT) and noninvasive prenatal testing (NIPT) are prenatal tests that provide information on a developing baby’s risk for certain chromosomal differences (anomalies). The screening is a blood test that evaluates substances in the blood (analytes), and NT is a sonogram that looks at nuchal translucency in the back of the fetal neck. Noninvasive perinatal testing (NIPT) is a newer method that provides a result with a blood test only; a first trimester ultrasound is still recommended.

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Everything You Need to Know About the First Trimester Screening

While most providers recommend this screening as part of standard prenatal care, it’s optional. Some parents-to-be seek comfort from the screening, while others may wish not to do it at all. Whatever your choice, it’s 100 percent up to you.

First Trimester Maternal Serum Screening Using Biochemical Markers PAPP-A and Free β-hCG for Down Syndrome, Patau Syndrome and Edward Syndrome

The first trimester screening programme offers a noninvasive option for the early detection of aneuploidy pregnancies. This screening is done by a combination of two biochemical markers i.e. serum free β-human chorionic gonadotrophin (free β-hCG) and pregnancy associated plasma protein A (PAPP-A), maternal age and fetal nuchal translucency (NT) thickness at 11 + 0–13 + 6 weeks of gestation.

First Trimester Screening Tests: What to Expect

Sometimes these tests are looking for general information, while other times they are conducted to look for something specific. For the blood test, two substances are looked for in the pregnant woman’s blood. The first is the level of pregnancy-related plasma protein-A (PAPP-A) in the placenta. If the number is too low, it might mean the baby is at risk for some type of chromosomal defect. The second test looks for a hormone called the human chorionic gonadotropin (hCG). Much like PAPP-A, an abnormal number might mean the fetus is at risk for a chromosomal defect. Neither of these tests mean for certain that the fetus will have some type of abnormality. It just means they might be at risk of it.

First Trimester Screening: Why It's Important

Detecting potential risks as early as possible is one of the primary reasons why first-trimester screening is so important. The screening assesses the baby's risk for specific conditions, particularly Down syndrome (trisomy 21) or Edwards syndrome (trisomy 18). By identifying genetic abnormalities, chromosomal disorders, and the risk of certain congenital disabilities early on, healthcare professionals can provide appropriate care and interventions.

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American Pregnancy Association

In babies who are at an increased risk for chromosomal abnormalities, increased fluid is often found in the nuchal translucency. Abnormally high or low hCG and PAPP-A levels are also often found. The first-trimester screen combines the results from these three measurements (nuchal translucency, hCG, and PAPP-A) with maternal age risk factors and determines an overall risk factor for chromosomal abnormalities.

Children's Hospital of Philadelphia

There are three parts of first trimester screening: Ultrasound test for fetal nuchal translucency (NT) Nuchal translucency screening uses an ultrasound test to examine the area at the back of the fetal neck for increased fluid or thickening. Two maternal serum (blood) tests The blood tests measure two substances found in the blood of all pregnant women: Pregnancy-associated plasma protein-A (PAPP-A) - a protein produced by the placenta in early pregnancy. Abnormal levels are associated with an increased risk for chromosome abnormality. Human chorionic gonadotropin (hCG) - a hormone produced by the placenta in early pregnancy. Abnormal levels are associated with an increased risk for chromosome abnormality.