Down’s Screening in First Trimester Pregnancy
By Audrey Mendenhall RT, RVT, RDCS, RDMS
Sound Health Imaging
In 1866 Langdon Down reported that in individuals with trisomy 21, the condition that came to bear his name, the skin appears too large for the body, the nose is small and the face is flat. In the last decade it has become possible to observe these features by ultrasound examination in the third month of intrauterine life.
The nuchal translucency is a space located behind the fetal neck. Approximately 75% of trisomy 21 fetuses have an increased nuchal translucency, which can be observed during an ultrasound exam. Approximately 70% of Down’s babies also have an absent nasal bone which can be detected in a first trimester ultrasound.
The Fetal Medicine Foundation directed by Dr. Kypros Nicolaides of London, UK has developed a protocol for first trimester genetic prenatal screening that combines a detailed fetal ultrasound exam during 11-13 weeks gestational age for nuchal translucency measurement, nasal bone and other fetal abnormalities. In addition to the ultrasound exam a blood sample is collected via a finger-stick. The dried blood sample is analyzed for free-beta subunit of hCG, a hormone found in the blood of pregnant women, and Pregnancy Associated Plasma Protein-A (PAPP-A) levels, a protein found in maternal blood. A first trimester genetic screen for the detection of trisomy 21 utilizing ultrasound only has a detection rate of approximately 80%. However, the detection rate increases to 91-95% with the addition of the free beta/PAPP-A blood test to the detailed ultrasound exam.
The Ultrascreen or Early Screen is the earliest, safest and most accurate one step prenatal screening test. A recent practice bulletin released by the American College of Obstetricians and Gynecologists endorses offering first trimester screening for fetal chromosomal abnormalities to all pregnant women, not just those over the age of 35 and at an increased for risk for having a baby with Down’s. The bulletin states that first trimester screening using nuchal translucency and biochemical markers result in higher detection rates than the second trimester triple or quad screen blood test. In order for the screening to be effective, the nuchal translucency must be done in a precisely defined manner by ultrasound professionals who have undergone appropriate education and training and are certified by the Fetal Medicine Foundation.
This is a new test available to pregnant women. Most women prefer screening in the first rather than the second trimester of pregnancy. This early screen option enables parents to find out earlier if a chromosome abnormality is suspected. Many parents in Montana, when faced with a chromosome abnormality, choose to parent. Studies have shown that parents who find out about abnormalities prior to delivery are better prepared and more successful at parenting.
An Early Screen has been endorsed by the American College of Obstetricians and Gynecologists as the standard of care and is covered by insurances. In Helena, Sound Health Imaging employs ultrasound professionals certified by the Fetal Medicine Foundation for performing this test. The Early Screen utilizing a detailed ultrasound exam and the dried blood component is only available at Sound Health Imaging. For more information contact our Helena office at 406-442-6356 or our Butte office at 723-0023