02/05/2014 01:44 pm ET Updated Apr 07, 2014

First Trimester Screen: More Questions Than Answers

It had been a couple of years since I was pregnant with my first child when I became pregnant with twins last year. With my first pregnancy I did no prenatal testing besides an Ashkenazi panel of genetic disease markers in my DNA, and then my husband got tested to check whether he was also a carrier for the one ultra-rare disease found lurking in my DNA. But with the twins, I did much more testing for two reasons: I had lost several pregnancies, and I had crossed the formidable 4-0 age barrier.

I decided to move forward with the First Trimester Screen when one of the OB/GYNs in my practice suggested it. The test is considered noninvasive, even though they poke a needle into your arm to measure the level of hormones hCG and PAPP-A in your blood. Besides that, they take two other factors into consideration: an ultrasound evaluation to measure the fluid behind the baby's neck (nuchal translucency) and the mother's maternal age. According to the American Pregnancy Association, they churn all these numbers through some sort of algorithm and spit out two probabilities: your chances of having a baby with Down's Syndrome and your chances for Trisomy 18.

In hindsight, I wish I had done more research. What I did not fully realize beforehand was that the First Trimester Screen returns more false positives as women get older, is less accurate for women carrying multiples, and is not a true diagnostic test. First things first, a screen does not tell you anything definitive, only a probability of getting a disease. If you want to know for sure whether your baby has Down's or Trisomy 18, you're looking at a procedure that's a lot more invasive because they need to get a sample of the baby's DNA. Second, the blood tests are not as accurate for multiples. The screen was developed for singletons and not for mothers carrying more that one baby. According to the Mayo Clinic, "In twin pregnancies, the risk for Down syndrome is approximated, using twin-adjusted medians. A specific risk for trisomy 18 cannot be calculated; therefore, results for trisomy 18 are reported as either screen-negative or screen-positive. Risks for triplets and higher multiples cannot be calculated." Third, according to a 2001 article in the British Journal of Obstetrics and Gynaecology (don't you just love the British spelling?), the false positive rate for Down's Syndrome at age 40 is almost 1 in 4 and by 45 it's over 50%.

When the OB/GYN entered the room all doom and gloom with the test results, telling me that I had to get more testing and meet with a genetic counselor because both babies had a high probability of a chromosomal abnormality, I asked him what the probabilities would be if we took age out of the equation. After all, my fertility doctor had told me I had the reproductive organs of a 30-year-old. He couldn't give me an answer, which I must admit made me a little skeptical about the screen's black box algorithm. (Incidentally, I later found a website where I could plug different numbers into the algorithm and play with the results. As they say: garbage in, garbage out!)

With the high false positive rate for women over 40, I couldn't understand why I was advised to get screened in the first place. My OB/GYN conceded that the results should be taken with a grain of salt -- before ever drawing my blood or getting my ultrasound, the chances were pretty high that my age was going to get me dinged as being high risk. The only thing going for this test was that it's non-invasive.

My doctor suggested I go for a CVS, a test whereby they remove a bit of the placenta. But guess what? The American Pregnancy Association does not recommend it for twins! And it doesn't even have the benefit of being non-invasive. So, after all the time and money spent on the First Trimester Screen, I went for a totally invasive amniocentesis instead. I had always planned to, and I was annoyed that my doctors bothered to administer the First Trimester Screen. What was the point? Did they do this to make more money or as a way to shield them from liability? Or did they just prescribe a test as rote procedure without thinking if it was appropriate for me?

In the future, I think medical providers should thoroughly discuss the pros and cons of each test before they start administering them. In my opinion, any mother over 40 or mothers carrying multiples should pass "Go" and head straight to the amniocentesis if they believe that it will bring them peace of mind and warrants the risks. That would take the first trimester screening, the quad screening, and the CVS off the table, and save everyone time (and your money). For me, calculating my chances of a problem is pointless. Determining whether or not there actually is an issue prepares me to make informed decisions.

I was fortunate that my amnio results came back fine and I was able to breathe a lot easier afterward. Next time (if there is a next time!), I will be better informed and better prepared to make decisions about which prenatal testing procedures are right for me.