A fully integrated screen is a combination blood test and ultrasound to detect genetic conditions such as Down Syndrome and Trisomy 18 (in both conditions the baby carries an extra chromosome), or birth defects, such as a neural tube defect (a condition where the spinal cord and sometimes brain do not form correctly) or an abdominal wall defect (where the belly does not close completely and some or all of the intestines develop outside the body).
Fortunately, these conditions are not very common, but they can be devastating when they do happen. Babies with Trisomy 18 are severely mentally handicapped and people with Down syndrome (Trisomy 21) have intellectual difficulties and a greater chance of medical problems, such as heart defects. The problems encountered with neural tube defects range from weakness in the legs and problems with bowel and bladder function all the way to an almost complete absence of brain formation (a condition called anecephaly).
As mentioned, the risks of these conditions are low. For example, the risk of having a baby with a neural tube defect is 1-2/1,000, the risk of Down syndrome is 1/800, the risk of Trisomy 18 is 1 in 3,000 to 4,000, and the risk of abdominal wall defects is about 1/4,000.
Why know about these conditions in advance?
Some women might chose to terminate their pregnancy. However, even for those parents who would not choose termination having this kind of information can be very helpful and even life-saving for a baby. For example, the risk of heart defects is higher among babies with Down syndrome. So, a baby with Down syndrome will have a special ultrasound called an echo during the pregnancy to screen for heart defects. If one were present, there might be a recommendation to deliver at a hospital that is capable of performing heart surgery (it would depend on the specific defect). A baby with an abdominal wall defect called a gastroschisis should be delivered by c-section to have the best chance after birth.
In addition, knowing your baby might have medical challenges, while very hard at first, will help you plan after delivery. For example, a baby who will need complex surgery may not be able to go to day care.
The results of screening tests are reported in risk. The risk is determined using the results in a complex calculation that also includes mother’s age, race, weight, how far along in the pregnancy, twins, and even smoking status. For example, a result might be a risk of Down Syndrome of 1/20 (or 5%). While that still means there is a 95% chance the baby does not have Down Syndrome, 5% is much higher than the baseline risk.
If the risk is elevated, the only way to know for sure if something is going on is a test called chorionic villus sampling or CVS (done in the 1rst trimester, and is a small sampling of placental cells) or an amniocentesis, withdrawing some amniotic fluid for testing (can be done after 14-15 weeks). The risks of CVS and amniocentesis are small, but definitely there. The risk of miscarriage with CVS is 1 in 300 and the risk of miscarriage with an amniocentesis is less than 1 in 300.
There are actually 3 types of screening tests:
A full integrated screen. This is the full meal deal. A blood test between 10 weeks and 13 weeks 6 days, a special ultrasound called a nuchal translucency between 11 weeks 2 days and 14 weeks 2 days, and another blood test between 15 and 20 weeks. This screening method will pick up the greatest number of babies with birth defects, Down Syndrome, and Trisomy 18 (although no screening test is 100%). If the 1rst blood test + the ultrasound indicate a higher risk, then the preliminary report will be given to you. This is because some women might want a CVS test so they can make a decision earlier in the pregnancy. Others may chose to wait for the 2nd blood test and even an ultrasound at 18 weeks so they have more information to help them decide about an amniocentesis. There is no right or wrong answer.
A serum integrated screen. This is just the two blood tests described in the full integrated screen without the ultrasound. There are no results until both tests are done. Because the results are not available until 14-15 weeks, the only option for further testing is an ultrasound and amniocentesis.
A quad marker screen. This is just the blood test between 15 and 20 weeks. Typically this test is offered to women who don’t have their first prenatal visit early enough to get either the full integrated screen or the serum integrated screen. This test will identify fewer positives than the serum integrated screen and the full integrated screen.
It is important to remember that most of the time someone screens positive it is not a genetic abnormality. Even a 25% chance of Trisomy 18 means there is a 75% chance everything is OK. It’s just different people feel differently based on the numbers. Some women want a CVS or amniocentesis for a risk of 1% and others decline further testing if the ultrasound looks OK (this help lowers the risk, but only an invasive test like CVS or amniocentesis can tell for sure).
Want more detailed information? Check out Kaiser Permanente Northern California’s web site. It is filled with great info as well as picture.
(Remember, this blog is not individual medical advice)