Week 17: Amniocentesis

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This is your Pea in the Podcast for week 17 of your pregnancy. I'm Bonnie Petrie joined by Dr. Laurie Swaim, an obstetrician with Houston Women's Care Associates in Houston, Texas.

Sometime between now and week 20 your baby will begin to hear. So now he or she will hear all of those long conversations you've been having with them, all those sweet songs you've been singing. Your baby will recognize and respond to your voice after birth so talk away. In fact, the world your baby gets used to hearing in the womb is pretty noisy, between your voice and your heartbeat, blood flow and breathing, some babies will have trouble getting used to the relative quiet outside after they're born and will need to have some white noise playing in the background in order to get any sleep as they acclimate to life in the world. There is some evidence though that fetal exposure to noise that is too loud, so loud you have to speak loudly to be understood, well it could damage their developing hearing so be careful of that. Some people wonder if playing music for the baby will affect their baby's development. The answer is nobody really knows, but if you enjoy listening to music, do continue. A relaxed mommy makes for a happy baby.

What else is your baby doing now? Well it is beginning to put on a little bit of fat, it will take the next several months for the baby to develop into the chubby cherub you will deliver though. The fat will account, at that time, for 2% - 6% of your baby's total body weight and will help maintain their body temperature when they're born. Your baby right now is about the size of a small pomegranate.

How about you? Well your uterus continues to push upward right now; it's about one and half to two inches below your belly button. You may notice a pooch there, maybe your partner does too, but most people probably won't notice you're pregnant. As your uterus continues to grow it will start to push other organs, including your intestines, off to the sides and before you know it, it will take up most of the space in your abdomen.

Now this week you may also consider another prenatal test, the amniocentesis. Now Dr. Swaim says 17 weeks is smack dab in the middle of the safest zone to do this particular invasive test. "Amnios can be done early, they can be done at less than 15 weeks but the risk is higher, so they're typically done between about 16 and 18 weeks and some do them later. I mean obviously there can be done throughout the entire pregnancy but for purposes of genetic amnio they're typically done, at least in our area, at 16 to 18 weeks. We don't typically do them after 24 weeks for prenatal diagnosis unless that is the first time that there may be a recognized abnormality of the baby and it would be important to know what the chromosomes are. We schedule them at about 16 to 18 weeks." Now a lot of women pass on this particular test because there is some risk of miscarriage, it is a small risk, even smaller than doctors used to think, "The risk of any complication was thought to be around somewhere around between 1 and 200 to 1 in 280 and now it's thought to be probably half that. So, it's come down when people start to look at the data and people do these constantly so they're good at them." But that risk is more than no risk so why do it? Well some women want to know in advance if their baby will have special needs so they can begin to prepare for the challenges they may face. This test gives you definitive answers. Sometimes you can discover an abnormality that can benefit from prenatal treatment. Also knowing what's going on with your baby allows you to tailor your prenatal care, your delivery and your baby's pediatric care to suit their special needs. Now sometimes if a structural problem has already been noted in your baby, an amnio will give you important additional information, "They can have what we call a diaphragmatic hernia or have gastroschisis, you want to know that before because the baby's going to be delivered in a tertiary care center and the parents should meet with the pediatric surgeons beforehand. In some of those instances those babies are more likely to have a chromosomal rearrangement problem so we may suggest an amnio then because if those babies have, for example, trisomy 18 or 13 then the outcome is completely different." Now babies with trisomy 18 and trisomy 13 will die after they're born. A situation like this is one of those in which a mom may decide to terminate her pregnancy. They may not and that is fine but that information would influence the decisions their doctors make while managing their pregnancy and ultimately their delivery. "If in fact the baby has a lethal anomaly then we wouldn't for example give the mom any medicine to stop preterm labor, we would never do a cesarean for a baby that wasn't going to live, you might not monitor that baby in labor, what have you. We would probably deliver a vaginal breach, we would if the baby wasn't going to live, that kind of thing. Not that it's necessarily bad to deliver vaginal breach in a healthy baby, I don't want to give that impression, but there are some medical decision making, but trisomy 18 and trisomy 13 are not common enough that we would suggest that everyone would have an amnio just so that we have that information. I think that I would only bring that up in the scenario where some form of testing, be it ultrasound testing or blood testing, made me have an increased index of suspicion that this baby may have something seriously wrong with it."

So who might consider having an amniocentesis? Well a mom who will be 35 years old or older on her due date, the risk of having a child with a chromosomal abnormality rises as a woman ages. Also if your nuchal scan or your first trimester screen, or your recent quad screen, came back with results outside of the normal range then you might want to have an amnio to get some definitive answers. You might consider the test if you've previously been pregnant with a child with a birth defect. Dr. Swaim says you might also have an amnio if you or your partner has a chromosomal abnormality or genetic disorder. "There are plenty of people who walk around whose chromosomes are not arranged normally but they're fine because they have all their genetic material. But then it becomes hard to reproduce and some of those people may want an amnio to make sure that their genetic material lined up in such a way that's compatible with life." Also if you and your spouse are both carriers of a recessive genetic disorder like cystic fibrosis or sickle cell disease, you might want to consider an amniocentesis.

So what happens when you get an amnio? Well you'll first get an ultrasound to identify the location of the placenta and the best pocket from which to draw fluid. Your abdomen will be cleaned over that area and numbed. Using ultrasound, a long skinny needle is guided into that pocket of fluid and about two tablespoons are drawn out for testing. The needle's withdrawn, your baby's heart rate is checked, you get a band aid and the test is done. That all takes about a half and hour. You may feel some cramping after the procedure and you'll want to take it easy for the rest of the day of test and avoid heavy lifting for the next couple of days. You may also be told to avoid sex and air travel after an amnio. Your doctor will talk to you in detail about what's normal and what's not normal and what things you can and can't do after the test.

Another peek into your baby's development this week: well babies are often seen batting the amnio needle on ultrasound. Because of the continuous ultrasound guidance it's very rare for the needle to get close to your bean and even more rare for any sort of injury to occur but if your curious child does happen to catch that needle they're batting at, they're likely move away quickly from the first foreign object they've ever touched. So that's it, week 17, you have 23 weeks to go before week 40.

That's your Pea in the Podcast for week 17 of your pregnancy. Dr. Swaim and I look forward to talking to you again next week. Enjoy this week and for a transcript of any of our Pea and the Podcasts go to our website peainthepodcast.com. For Pea in the Podcast, I'm Bonnie Petrie, thanks for listening.