First Trimester Pregnancy Screening
First trimester screening is an effective way to check for any chromosomal abnormalities, prior to the second trimester (approx. 15 weeks). This screening involves two steps:
- You will receive an ultrasound by a certified professional to measure an area at the back of your baby’s neck, called the nuchal translucency.
- We will obtain a blood sample through a finger stick to analyze the amount of two chemicals present: free Beta-hCG and PAPP-A.
You must be pregnant between 11 and 13 weeks, six days counting from the first day of the most recent menstrual cycle, to receive a first trimester screening. Until recently, prenatal screening was not possible prior to the second trimester. This screening provides you an opportunity to find out early on if your baby is at an increased risk of having a chromosome problem.
Specific risks for Down syndrome and trisomy 18 are calculated by combining the ultrasound measurement and the results of your blood test. Both conditions are caused by the presence of an extra chromosome, which results in mental retardation and various birth defects.
There are some instances where first trimester screenings are not possible. This can happen if your baby is not in a position that allows the nuchal measurement to be obtained, or if the pregnancy dating is over 13 weeks, six days. If you fall into this category, you do have the option of a second trimester screening, also known as the Quad screen.