Optional First Trimester Screening Tests

Before your next appointment, you should consider whether you are interested in having any of the optional testing done.

Screening for Chromosomal Abnormalities

The majority of optional tests are focused on early diagnosis of chromosomal abnormalities, the most common being Down syndrome.  The chance of having a child with a chromosomal abnormality increases with age (see attached). Humans are born with 46 chromosomes in each cell of the body. The mother and father each donate 23 chromosomes which then combine to create your baby. A chromosomal abnormality results when there is a change in the number or structure in one or more than one of the chromosomes.  The chance of this happening increases with maternal age.

With Down Syndrome (also known as trisomy 21), an extra copy of chromosome number 21 is present. About 1 in 800 babies is born with Down Syndrome.  All of these babies will have some degree of mental retardation, usually in the mild to moderate range.  Babies with Down Syndrome can also have defects in the heart and/or digestive tract.  They have distinct physical features as well, like their facial structure, but this does not affect their health.

Trisomy 13/18 is much more rare than Down Syndrome, affecting 1 out of every 6000 babies. These babies are born with an extra copy of chromosome 13/18.  Unfortunately, nine out of ten babies with this defect will die before their first birthday.  Those who live longer are severely mentally retarded and often have other serious health problems, including heart defects and growth disorders.

Choices for Screening for Chromosomal Abnormalities

If you decide you would like to screen for chromosomal abnormalities, you have invasive and non-invasive tests to choose from.  The best of the non-invasive tests is the nuchal translucency (NT).  This test is collected between 11-14 weeks and is a blood test from the mother and a fetal ultrasound.  There is no direct risk to the fetus of this test. The main risk is the possibility of false positive and false negative results.  The Quad Screen is also a non-invasive test. It is for those who would like a non-invasive test and is performed between 15-20 weeks.  It does not involve a specific ultrasound.  Your anatomy scan, around 18 weeks, is also a type of screen for chromosomal abnormalities.  Chance of false positive and false negative results is higher with the Quad Screen.

There are also invasive tests that involve analyzing a small biopsy from the placenta or a sample of the amniotic fluid. While the results are very reliable (99.5% accuracy) there is a potential for the test to cause the pregnancy to miscarry.  These are typically offered to women who are advanced maternal age (age 35 or older) because the risks of miscarriage are similar to the risks of carrying a child with a chromosomal abnormality.

Chorionic Villus Sampling (CVS) is usually done between 10-12 weeks gestation.  A small sample of chorionic villi which are part of the placenta are biopsied.  The biopsy is collected using ultrasound and a needle placed either through the abdominal wall or the vagina to collect the sample. This is done in an office setting. If you choose this option, we will refer you to either Duke or UNC for it to be performed. The advantage of this test is that results are back sooner than amniocentesis. The disadvantage is that risk of fetal loss (miscarriage) is higher, around 1%.

Amniocentesis is usually done after 15 weeks. It involves using ultrasound to place a needle through the abdominal wall and collect some of the fluid from around the baby. We can arrange for it to be done in our office.  Risk of pregnancy loss after amniocentesis is performed is approximately 1/300 - 1/500.

Screening for Open Neural Tube Defects (like Spina Bifida)

An open neural tube defect occurs when the baby’s spinal cord or brain does not form properly.  This occurs in 1 out of every 500-1000 births.  Spina bifida is a type of open neural tube defect when an opening forms in the developing spine. This opening may not be covered by skin and the exposed nerves may be damaged.  Depending on the location and severity of the defect, the child may have difficulty walking, problems with bladder or bowel control, a buildup of fluid around the brain or mental retardation.  Some of these babies are candidates for surgery even before delivery that can help decrease these complications. These can be diagnosed before delivery with several methods including the quad screen, an AFP measurement, focused ultrasound or amniocentesis.