Blood-tests Explained


Disclaimer:

This website is intended to assist with patient education and should not be used as a diagnostic, treatment or prescription service, forum or platform. Always consult your own healthcare practitioner for a more personalised and detailed opinion

First Trimester Screening


At a Glance

Why Get Tested?

For pregnant women, to assess the risk of your baby having a chromosome disorder, such as Down syndrome (trisomy 21) or Edwards syndrome (trisomy 18)

When to Get Tested?

Usually between 11 and 14 weeks of pregnancy

Sample Required?

A blood sample drawn from a vein in your arm or a blood spot collected on special paper from a finger stick; a nuchal translucency requires a special ultrasound exam.

Test Preparation Needed?

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

The Test Sample

What is being tested?

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 measurement made by ultrasound. The ultrasonagrapher 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 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 (transabdominally) 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.

The Test