First Trimester Screening
Come prepared for your first trimester screening.
- Please have a full bladder when you come for your appointment
- Please know which laboratory is preferred by your insurance company
Our office utilizes the sequential screening labs for our first trimester screening.
What is Sequential Screening?
Sequential Screening is a two-stage screening procedure offered during pregnancy to identify women who are at increased risk of having a baby with Down Syndrome. It also permits screening for open neural tube defects, such as open spina bifida, and the identification of pregnancies at high risk for trisomy 18.
The first stage of Sequential Screening is offered between the 10th and 13th weeks of pregnancy and requires a blood sample and an ultrasound examination. The blood sample is used to measure two proteins that are found in a pregnant woman's blood: pregnancy-associated plasma protein A (PAPP-A) and human chorionic gonadotropin (hCG). An ultrasound exam of the baby is performed to measure the nuchal translucency (NT). Nuchal translucency refers to a collection of fluid in the back of the baby's neck. Babies with Down syndrome and trisomy 18 tend to have NT measurement that are larger than those of babies without these conditions.
Results of the blood and NT measurements are combined, and risk for Down syndrome and trisomy 18 is determined. If a baby is found to be at very high risk for either Down syndrome or trisomy 18, then diagnostic testing is offered. Most women (over 99%) will not be in this very high-risk group, and they proceed with the second stage of Sequential Screening.
The second stage of Sequential Screening is offered between the 15th and the 21st weeks pregnancy and requires a blood sample to measure four substances found in a pregnant woman's blood: alpha-fetoprotein (AFP), hCG, unconjugated estriol (uE3), and dimeric inhibin A (DIA).
The NT measurement and the measurements from both blood samples are then combined with information about you, such as your age and weight, to determine your baby's final risk for having Down syndrome. The AFP measurement is used to screen for open neural tube defects, and the combination of the different makers may identify babies at increased risk for trisomy 18.
- Down Syndrome, also called trisomy 21, the baby has an extra copy of the #21 chromosome. All babies with down syndrome have some degree of mental retardation and often have physical abnormalities such as heart defects. About 1 in 800 babies is born with Down syndrome. Sequential Screening is expected to detect 92% of pregnancies with Down syndrome in the early second trimester with 3.5% of unaffected pregnancies having positive results (ie, a false-positive rate of 3.5%.)
- Trisomy 18 is also known as Edwards syndrome. Babies with this condition have an extra copy of the #18 chromosome. Trisomy 18 causes sever mental retardation and physical abnormalities. Most babies with Trisomy 18 die within the first year of life. Trisomy 18 is rare, occurring 1 in every 7500 births. Sequential Screening is expected to detect 90% of pregnancies with trisomy18 with little increase in the false-positive rate over the rate of 3.5%.
- Open neural tube defects (ONTD), such as open spina bifida, occur when the baby's neural tube, or spine, does not close completely during development. About 1 in 1000 babies is born with open spina bifida. The effects of open spina bifida range from bladder control problems to paralysis and hydrocephalus. Screening is performed by measuring AFP levels in the second trimester of pregnancy and can identify 80% of pregnancies with open spina bifida with a false-positive rate of 1% to 3%.