Triple Screen

July 21, 2011

This patient is a 23 year old Gravida 1 who presents for prenatal care at 8 weeks gestation. She has a completely normal history and physical exam is compatible with an 8 week gestation. The pelvis is of normal configuration and size.

This patient is a 23 year old Gravida 1 who presents for prenatal care at 8 weeks gestation. She has a completely normal history and physical exam is compatible with an 8 week gestation. The pelvis is of normal configuration and size. Lab work reveals Rh positivity, Rubella immunity, and no abnormalities. She is provided with the usual information and given an appointment to return in 4 weeks.

At her second visit at 12 weeks, she has gained 2 pounds, has no complaints, her uterus is palpable just above the pubic symphysis, and fetal heart sounds are heard with the doppler stethoscope. Everything continues to progress normally and she is instructed to return in 4 more weeks.

Now at 16 weeks, she still has no complaints. The uterine fundus is now half way between the pubic symphysis and the umbilicus. Fetal heart tones are again heard. At this visit, an ultrasound is ordered and she is offered a "Triple Screen". "What's a triple screen, Doc?" she says. I have already sat down and made myself real comfortable, since if she hadn't asked, I was going to tell her all about it anyway.

"A triple screen," I say, "is a blood test that is done to look at the risk for a pregnancy having a fetus with either Down syndrome or a spina bifida. This is not a test that tells us the baby does or does not have either one of these defects. This is a test that tells us the baby is at high risk or low risk for one of these problems. The triple screen measures the levels of three (hence triple) hormones in the pregnant woman's blood stream. These are alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol. The fetus and/or the placenta plays at least a major role in the production of each of these, so they reflect the fetal condition to a certain extent. e.g. alpha-fetoprotein is elevated in fetuses with spina bifida and certain other brain and spinal cord conditions and it is low in may cases of Trisomy 21(Down Syndrome)."

"So, if we do this test the report will come back and say that in a 23 y/o African-American at 16 weeks who has these levels of these three hormones, the risk of her having a baby with Trisomy 21 is 1 in 10,000. This means that you are at extremely low risk, not no risk but very low risk. On the other hand it could come back and say the risk is 1 in 10 that this baby has Trisomy 21. This would mean the risk is high, not absolute but high." She now says, "Why do the test if it doesn't give us an answer?" My response is that if it says low risk we accept that low risk and do nothing further. If the risk is high, then we would offer her the test that does give us a definitive answer; an amniocentesis with fetal karyotype.

"Then why not do an amniocentesis on everyone?" she asks. I respond that the amniocentesis is an invasive procedure with some risk to the fetus and even a little risk to the mother. In addition it costs a lot more to do.

She then asks me, "Why should I do this when I am going to have an ultrasound anyway?" "Because," I replied, "an ultrasound is not diagnostic of Trisomy 21. Sometimes, one can see things on ultrasound that make one suspicious of Trisomy 21. Even if some of these things are seen, the incidence of Trisomy 21 is around 5%. So if one does see them, an amniocentesis is then recommended. In other words, the ultrasound is also a screening test which will pick out pregnancies that are at high risk for Trisomy 21."

At this point, I also let her know that there are other things that can lead to false triple screen results. The most common of these is wrong dates. In her case we don't need to worry about that because of her early visits and the ultrasound. Also, other fetal abnormalities such as abdominal wall defects may cause the triple screen to be abnormal.

She now says, "Gee, you know I don't believe in abortion, even if the baby has Trisomy 21. So why do this test?"

"Many women who know they have a Trisomy 21 baby do not abort. It is very helpful to know ahead of time. If you know, then there are support groups to which the expectant parents can be referred to help them prepare ahead of time for the problems that they will be facing as they raise this "special" child," I explain.

She decides at this point that she would like to go ahead and get the procedure done. We draw the blood and send it off to the lab. Four days later the triple screen report is called back to my office and I am informed that her risk of having a trisomy is 1 in 50. This certainly is an increased risk. She is now a candidate for Counseling and amniocentesis. I call her and set up the appointment to come in the next day with her husband.

After they come in, we talk about the results of the test. I explain that this means that there is a 1 in 50 chance of the child having a trisomy and a 49 in 50 chance of it not having a trisomy. I also explain about an amniocentesis and its risks and benefits. We discuss that the risk of causing a loss of the pregnancy are less than the risk of a trisomy being present. We also talk about how the procedure can not tell her that the child is normal, just whether or not it has a trisomy. At this point, we repeat the ultrasound so that we can do the amniocentesis without going through the placenta. After cleaning her abdomen, I then insert the needle into the amniotic cavity, while watching on the ultrasound. This allows me to direct the needle to a place where there is a collection of fluid and away from the fetal head. I withdraw about 20 cc's(2/3 of an ounce) of slightly yellow clear appearing fluid. I put this into a pre labeled container which is then sent to the cytogenetics-genetics lab. Following the procedure, we watch the site where the needle entered the uterus and there is no bleeding seen. After placement of a Band-Aid, she goes on home with an appointment to return in 10 days for the results.

Ten days later they return and I have to tell them that their fetus has Trisomy 21. They then immediately want to know; Does it have a heart defect? (I don't think so but it could), Will it have severe mental retardation? (I don't know how severe it will be), and Will it develop Leukemia? (I don't know.) These are all questions that the amniocentesis can't distinguish. They now ask what their options are. I explain that there are basically two options; termination or not. They want more information about both of these options. I explain that if they do not terminate, we will get them in touch with a support group of parents of children with Trisomy 21. Again they want to know how severely affected this fetus is and I have to again explain that we don't know. They want to hear about termination. I explain we would start by inserting a prostaglandin suppository into her vagina which would cause her to start having contractions which would lead into a labor like situation. We would relieve her pain with narcotics and or an epidural. Eventually, she would pass the fetus and the placenta. After observation for a while longer, she would be able to go home. They asked for time to think about this. I said that there was time to do that because she was only 18 weeks and we had up to 24 weeks to do this. However it would be better to do it sooner than later because the further along the pregnancy is the greater is the risk of complications.

Two days later, they called and told me that they want to terminate the pregnancy. I say OK, I will have to call the hospital and arrange it. At 7 AM three days later she comes to the hospital and after starting an IV, I insert a prostaglandin suppository. Within a half hour, she is contracting and by three hours, she is contracting quite strongly. She requests an epidural for pain relief and this is provided. About 9 PM, she passes the fetus vaginally. 25 minutes later, she passes the placenta. Examination reveal an intact placenta and that she has no lacerations. Once the epidural wears off and she is able to ambulate, she is released.

Two weeks later when she and her husband come back to the office, they have many questions regarding the risk of recurrence. I explain that it is thought that she might have a slight increased risk with future pregnancies and that either CVS or amniocentesis would be offered. I also explained that with the research going on now, there may be other techniques available by that time.

One year later, she presented at 7 weeks gestation, had a CVS done at 11 weeks gestation (which revealed no Trisomy), and delivered a healthy baby girl at 39 weeks.


Discussion

This patient is an excellent example of how the triple screen allows us to diagnose about 65% of Trisomies at a stage early enough to terminate the pregnancy if so desired. While the highest incidence of Trisomy is in women over the age of 34, the largest number of pregnancies with Trisomy occur in women under age 35. This is because the number of women having pregnancies under age 35 is so great. The triple screen offers a non invasive method of determining which of those women under 35 are at increased risk for a Trisomy pregnancy, so that we can offer them the more risky and invasive procedure of amniocentesis.

The alpha feto-protein portion of the triple screen also allows us to screen for Neural Tube Defects. If the AFP is elevated and a neural tube defect is ruled out, then other things such as abdominal wall defects and Congenital Finnish Nephrosis must be ruled out. Once they are ruled out, the pregnancy with an elevated AFP and none of these defects, still has an increased chance of poor outcome from such things as unexplained fetal death and intrauterine growth restriction. So this is valuable information that allows us to start testing these pregnancies and to intervene when indicated.

I offer triple screening to all of my patients. About 10-15% decline to have it done for various reasons, but the rest agree to it. I talk to them about what it is and what it does not do. I also explain to them the procedure that would be followed if they were to have an abnormal test. This is one reason that many of them decline. They say that if the test were abnormal, they would not want to have an amniocentesis. In other words since they don't want to know the answer, they don't ask the question.