Talk to me about prenatal screening

[poppan]

I have an appointment tomorrow to get a dating u/s, and they talked me into doing genetic counseling (because I'm now officially of "advanced maternal age"--having hit 35 last year). If I'm in the right weeks, I might do the nuchal fold scan. My best guess is that I am 14 weeks along, but I don't know for sure.

I want to be prepared about any other testing... from what I remember last time, the quad screen (blood test) and if either that or the nuchal is positive, then an amnio. Last time I declined all these things because we went through so much to get pregnant that there was no way in heck I was going to risk an amnio. This time around I already have all the kids I want, this is uh, a big surprise, and I might be willing to risk an amnio... or at least want to consider the pros and cons.

Anyone have info, opinions, etc.?

[EdnaMarie]

I'm not an expert, but I'd refuse simply because of all the false positives, even with amniocentesis, and I just don't need that stress. Good luck, though.

[finnegansmom]

The nuchal fold US is only valid up to baby gestation of 13w6d so if you are 14 weeks already you are too far along. it's a screening test - not a diagnostic test. It only tells you based on blood work and the measurement of the "nuchal fold" at the back of the neck if you are at higher risk for getting a postive results from an amnio or CVS. The test won't give tell you a true positive or negative result. If your risk is 1:50 and your child is is born with normal chrosomes , it doesn't mean you had a "false positive", you were just one of the 49 other moms who had a good outcome.

If you plan on getting the US, prepare yourself for getting the amnio if your results are higher than your comfort level. You're only 35 - it's when you're 40+ that that risk due to age really goes up. And I'll just say, this is my 4th pregnancy being over 35...

Good luck in your decision.

[lillymonster]

There is no "positive" result, it determines risk. I got it done and my risks were much lower than the risk for most mothers my age. 1 in 700 compared to the risk they have figured of 1 in 90. I am not getting the amnio, and will never get it. Not because it won't change anything, but because the thought of poking a hole in my belly freaks me out. I know it's small, I know it doesn't hurt, but I am not doing it, just a personal thing.

Anyway, I am 40, and I comfortable with just the NT u/s. My midwife also said that doing additional testing later around 20 weeks (I believe that is the quad screen or sequential testing) will just give me false readings, so I am just doing the part of the blood test to test for neural tube issues and the anatomy scan at 20 weeks.

I had my first child at 36, btw, and only had the quad screen the first then, I refused amnio then and I was not offered the nt u/s at all.

[RedOakMomma]

skipping here from the OP...

We were in a similar spot. With our second pregancy, we declined all testing because we couldn't stand the risks of losing the baby. And that was with our first children (twins), too, who both have/had significant special needs from a genetic disease they both have. We just couldn't risk it.

But now, with baby #5 on the way, we took a look at our family and decided that we WANT to know as much as we can--including if there are any special needs or genetic issues we can discover before birth. I can't explain why we felt different, but we really did. We opted for the amnio.

The amnio came in conjunction with some genetic counseling, where basically we looked at our odds (based on an ultrasound scan and a the quad screen) of having a child with certain chromosomal abnormalities (and/or the genetic mutation our older sons have) VERSUS the chances of something bad happening from the amnio.

In our case, the quad screen and ultrasound came back with no findings at all, so the chromosomal stuff had very low odds to them (1 in 2,000 to 1 in 10,000 based on the analysis). The amnio, based on the perinatologist's records, had about a 1 in 750 to a 1 in 1,000 chance of something going wrong. If that had been the end of it, we might not have opted for the amnio:

1 in 2,000 risk of something being wrong vs. 1 in 750 risk of amnio harm = no amnio

BUT, for the genetic testing we wanted done, it looked like our risk for a repeat of that specific genetic illness was somewhere between 1 in 50 and 1 in 200. So:

1 in 50 of something being wrong vs. 1 in 750 of amnio harm = yes amnio

That was our reasoning.

The amnio was quick, the doctor was GREAT about showing what was going on, and confirming that the baby was fine afterwards. He said if something bad was going to happen (a leak, and infection, etc.) it almost always happens within 24 hours...and so I took it very easy for 48 hours.

When the results came back I was thrilled that we did the test. Having had the worries of genetic mutations in the back of my head for three pregnancies, being able to let go of that for this pregnancy has been such a gift. I know I can't guarantee our dd-to-be is healthy, but it sure feels great knowing that we discovered and know as much as we can. And at the very least, I KNOW she doesn't have the same mutation our oldest sons have. It's a great feeling.

[poppan]

Thanks for all the replies. Very helpful distinction between "positive" and an odds ratio... I had not realized that! Since I get to go to the genetic counselor first, I guess I will take the chance to ask some questions. What do you think about these:

For [insert name of test], out of 100 women:
1. how many get a "positive"/recommendation for further testing
2. of those, how many go on to have babies that don't have anything "wrong" with them
3. How many screen fine but go on to have a baby with an abnormality anyway (false negative)
4. what are the recommended steps if you get a high odds risk ratio
5. are there other ways to detect whatever we're screening for, such as with ultrasound, and are the alternate methods more reliable

From what I've read so far, I'm leaning towards a Level II u/s only, because I am so uncertain of my conception date and I understand the screening tests depend a lot on them entering in the right gestational date. I don't want a lot of stress over nothing. If they pick up something in u/s I might be open to an amnio despite the risk (1-2% -- is that for real?). Yeah I'm pretty freaked about the big needle in the stomach but we can barely deal with another baby, let alone a special needs baby (please don't flame me for feeling that way).

Redoakmomma--you said it so well, that is exactly how I feel. I want to know what I can know. Unfortunately I think I could literally be anywhere between 12 to 18 weeks (I didn't think I could get pregnant so have spent months waiting for my period--only when I started to show to myself did I finally pee on a stick!). So am shying away from the blood tests.

[RedOakMomma]

Amnio risk is somewhere between about 1 in 250 (so less than 0.5%) and 1 in 1000 (0.1%), depending on the skill of the practioner. Our perinatologist has a lot of practice with amnios, so his risk was around 1 in 750, though he said with most experts you should assume a risk between 1 in 500 and 1 in 1000.

The 1-2% risk info is outdated.

[jenifera2]

The amnio can be done any time after something like 15 weeks, so there's no harm in being "too far along" for that test if you decide to do it, unlike some of the screening options. But once you've had your dating scan the genetic counselor can tell you what options are still open to you.

And just to clarify an earlier point - there are no (or almost no) false positives with amniocentesis. It's a test that would be 100% accurate in what it tests for if not for the fact that humans are involved in the testing process. Generally it's said to be better than 99% accurate.

Your questions are good ones to start with for the counselor, though the answers to some are just math since screening tests are not diagnostic tests. A screening test that says that you have a 1/500 chance of having a baby with a chromosomal abnormality means that for 500 women with those same screening results, 499 would have babies with normal chromosomes and 1 would have a baby with abnormal chromosomes. That one woman did not get a "false negative" result, since there is no odds number that indicates "negative". It's all about chances.

The counselor will also likely tell you that there is no other testing that can tell you what you're looking to know. Ultrasounds can show markers for genetic abnormalities, but having those markers isn't conclusive that something is wrong, and not having them isn't conclusive that something is right. Also, that ultrasound happens pretty late, so if you would consider terminating a baby with chromosomal abnormalities, you might prefer to have a test such as amnio done as early as possible rather than waiting until 20 weeks or so for a level II u/s.

I think for many people it simply comes down to whether you need to know your baby's genetic status. If you are not comfortable moving ahead with that big unknown, then you'd want to strongly consider amnio. If you are comfortable moving ahead because you wouldn't do anything differently no matter the outcome, skipping amnio is a logical choice.

For us, not knowing would have added a significant amount of stress to this pregnancy, and it wouldn't have been enough to even have low risk screening results, so we skipped all preliminary screening completely and had an amnio done. We've come out on the wrong sides of the odds calculations too many times to be comfortable even if the screening had said 1 in 1000 chance of a problem, and we just wanted to know for sure. That said, making choices that balance risk and reward for your particular situation can often be very difficult.

[lillymonster]

Originally Posted by poppan

For [insert name of test], out of 100 women:
1. how many get a "positive"/recommendation for further testing

I don't know about the rest of the questions, but I do know that the place I went to likes to push that amnio. My odds were 1 in 700 for downs and something like 1 in 3000 or 7000 for trisonomy 18. For a 40 year old, normally they are 1 in 90. And they still recommended an amnio. Amnio is the only thing that is 100 or 99 percent accurate. I had it mentioned like 4 times after I said I was not interested - "well that is the only way to be accurate"