If your doctor has suggested amniocentesis -- a procedure in which some of the amniotic fluid around the fetus is removed for genetic testing -- you probably have a lot of questions and concerns:
Read on for answers to these and more.
When a couple finds out that they're going to have a baby, it's a cause for celebration. But for some couples, there are questions about the health of their newborn. With all the advances in medicine, doctors and their patients can learn a lot about the development of a fetus, and one of the tools that's commonly used is amniocentesis. This is a procedure which involves removing a small portion of the amniotic fluid which surrounds the fetus. It was first tried many years ago, and today is used in the second trimester to determine if certain birth defects are present.
Question: What is in the amniotic fluid that makes it so important for amniocentesis?
Answer: Those are fetal cells, cells that have actually shed from the fetus. They come from the skin, from the GI tract, from the lungs, and from the bladder. We're actually looking at fetal cells when we do testing from the amniotic fluid. So it's not the fluid per se that's important, but the cells in the fluid.
Question: What indicators would be a reason to suggest an amniocentesis?
Answer: The primary indicators for amniocentesis would be the mother being age 35 or older at the time of the delivery, a known family history for which genetic antenatal testing can be used to determine whether the baby is affected. A prior child who has been affected with a chromosomal abnormality or some other inherited condition. And, additionally, an abnormal ultrasound in and of itself could be an indicator for an amniocentesis.
And also, during the second trimester, we routinely offer triple screen tests, which includes looking at maternal serum alpha-fetoprotein, something called the free-beta, and an estriol level, to come up with a calculated risk which uses the patient's age, the number of fetuses she's carrying, and a variety of other parameters to calculate a risk. And if she's at increased risk, based on this particular blood test, then that would be an indication for proceeding with an amniocentesis also.
Question: Are multiple births an indicator for amniocentesis?
Answer: Multiple births in and of itself would not be. The criteria would be age, prior history, an abnormal fetus being picked up at the time of an ultrasound, or an abnormal triple screen.
Question: Could you explain what an abnormal triple screen means?
Answer: This is the blood test that is offered between 15 and 19 weeks, although performing the test earlier is better, because then you have time to do the additional workup. Again, looking at the three parameters that I mentioned, in order to come up with some numbers that determine whether the patient's at increased risk, for example, for Down syndrome, which is trisomy-21, or trisomy-18, or open neural tube defects.
The triple-screen test is one of those tests that is fairly much routinely done by most obstetrical practices. A lot of patients are worried about what they've been told. It's false negative or a false positive.
The terms false negative and false positive are misleading because the test actually recalculates your risk of having a baby with Down syndrome. It does not say "yes" or "no". Up until recently, all we had to deal with was maternal age. If we just use maternal age alone, 35 or older, we were picking up on 6% of Down syndrome. So we wanted to do something that would help us with the women 35 and younger. Over time we've come up with this particular test that will recalculate the risk.
What we use as the cutoff is the same risk as you would see with someone who was 35 or older. So if it turns out that your risk of having a baby with Down syndrome, based on the triple-screen, is 1 in 270, that's a 35-year-old's risk, then you're offered amnio. Now, think about that. If your risk is 1 in 270, that means 269 out of 270, it won't be Down syndrome.