What is PAPP-A?

Also Known As: Pregnancy-associated plasma protein-A (PAPP-A) with hCG, total or free beta subunit and nuchal translucency ultrasound The first-trimester screening is a combination of two blood tests and a special ultrasound that are used to assess a pregnant woman’s risk of carrying a baby with Down syndrome (trisomy 21) or Edwards syndrome (trisomy 18). Performing and evaluating them together, plus considering the woman’s age, increases both the sensitivity and specificity of the screening results.

Pregnancy-associated plasma protein-A (PAPP-A) is a protein produced first by the growing placenta. During a normal pregnancy, levels of this protein increase in the pregnant woman’s blood until delivery.
Human chorionic gonadotropin (hCG) is a hormone produced during pregnancy in large quantities by the placenta. Either free beta subunit or total hCG can be used in first-trimester screening. Levels of both usually rise rapidly in the pregnant woman’s blood for the first 8 to 10 weeks, then decrease and stabilize at a lower level for the remainder of the pregnancy.
Nuchal translucency is a measurement made by ultrasound. The ultrasonographer measures the fluid collection between the spine and the skin at the nape of the fetus’s neck. It is a procedure that requires a specially trained radiologist, proper alignment of the fetus, and careful measurement. It is not a routine ultrasound, and it is not a procedure that is available at every hospital or health facility. If the results of the first-trimester screening are cause for concern, diagnostic tests such as amniocentesis or chorionic villus sampling (CVS) may be recommended.

How is the sample collected for testing?

Blood is drawn from a vein in the woman’s arm or collected from a finger stick. The nuchal translucency ultrasound may be performed from outside the abdomen (transabdominal) or the probe may be inserted into the vagina (transvaginally).

Is any test preparation needed to ensure the quality of the sample?

You may be instructed to have a full bladder when having the nuchal translucency ultrasound performed.

How is it used?

The first-trimester screening is a combination of tests for PAPP-A, hCG, and nuchal translucency that are used to assess the risk that the fetus a pregnant woman is carrying has a chromosome disorder such as Down syndrome (trisomy 21) or Edwards syndrome (trisomy 18). The first-trimester screen is one of the options you may be offered for prenatal Down syndrome screening. Other options include the second-trimester maternal serum screen and the cell-free fetal DNA test.

One advantage of the first-trimester screen is that it gives expecting women the option of earlier screening. However, the first-trimester screen does not assess the risk of neural tube defects such as spina bifida. This may be assessed in the second trimester as part of the maternal serum screen (triple or quad screen) or on its own.

The screening approach a woman may choose depends on what technology is available and when she first seeks prenatal care. For more information about how first-trimester screening fits in with other screening options, see below.