Maternity - Pregnancy, part 5: Diagnostics: Ultrasound, Chorionic Villus Sampling, Amniocentesis

September 08, 2021 Updated: November 20, 2021 7 min read

In this article and video, we cover some diagnostic procedures performed during pregnancy: an ultrasound, chorionic villus sampling, and amniocentesis. These are important procedures to know about for your Maternity exams and the NCLEX.

This series follows along with our Maternity Nursing Flashcards which are intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI, and NCLEX.


An ultrasound is a non-invasive procedure that uses high frequency sound waves to visualize a developing fetus.

Ultrasounds are a standard part of prenatal care to confirm pregnancy, locate the pregnancy and ensure that it is in the uterus and viable. It is also used to date the pregnancy and assess fetal growth and development based on its size, and determine if there is a need for additional testing.

Types of ultrasounds

There are two types of ultrasounds done during pregnancy, a transvaginal ultrasound and an abdominal ultrasound.

Transvaginal ultrasound

A transvaginal ultrasound is performed using a transducer which is placed in the vagina, and is usually used early in pregnancy. It does not require the patient to have a full bladder as the bladder because of the location of the imaging.

Abdominal ultrasound

An abdominal ultrasound is the type that you may think of when you think of an ultrasound! An abdominal ultrasound uses the ultrasound device on the abdomen. This ultrasound is used during the second or third trimester of pregnancy.

An important patient teaching point is that this procedure requires a full bladder to better reflect sound waves.

Chorionic villus sampling (CVS)

A chorionic villus sampling is an invasive procedure that provides early diagnosis of chromosomal, metabolic, or genetic abnormalities.

A chorionic villus sampling might be indicated if a patient has a family history of genetic disease, or has a previous birth of a child with a chromosomal defect.

A chorionic villus sampling procedure is performed between 10-13 weeks gestation. In this procedure, a portion of the placenta is removed via the cervix (via catheter) or abdominal wall under ultrasound guidance. Rhogam is administered to Rh- mothers after the procedure (to prevent sensitization to fetal blood).

Some complications seen with a chorionic villus sampling are post-procedure bleeding, spontaneous abortion (miscarriage), chorioamnionities, or PROM. It is important for patients to weigh the risks and benefits of this procedure because of these potential side effects.


An amniocentesis is a procedure used to identify chromosomal abnormalities, neural tube defects, Rh incompatibility, and fetal lung maturity.

An amniocentesis might be indicated if the patient has a family history of chromosomal abnormalities, or an abnormal MSAFP. A therapeutic amniocentesis may be done for polyhydramnios.

An amniocentesis procedure is performed between 15 and 18 weeks gestation, and the patient must have an empty bladder beforehand. A sample of amniotic fluid is removed from the uterus via a long, thin needle inserted through the abdomen under ultrasound guidance. Rhogam is administered to Rh- mothers after the procedure.

Some complications seen with an amniocentesis are maternal or fetal hemorrhage or infection, PROM, amniotic fluid leakage, preterm labor, or miscarriage.

Full Transcript

Hi, I'm Meris, and in this video, I'm going to be talking to you about different type of diagnostic procedures which can be performed in pregnancy. Specifically, we're going to be talking about ultrasound, chorionic villus sampling, and amniocentesis in this video. I'm going to be following along using our maternity flashcards. These are available on our website So if you want a set, grab a set, and if you have one already, I would invite you to follow along with me. All right, let's get started.

So first up, we are talking about ultrasound, which is a very common diagnostic procedure performed in pregnancy. There's a lot of reasons it could be done. It can be done initially, to help locate the pregnancy, ensure it is in the uterus, ensure that it is viable, and we can actually date the pregnancy and see how far along the patient is based on the size of the embryo, of the developing fetus. And this is something that is considered non-invasive. It does not involve any sort of risk of infection or bleeding or anything like that, and it just uses sound waves to visualize the contents of a patient's body. So this is really, really common. You will also see that your patients may have something called an anatomy scan, usually between 18 to 20 weeks. And this is where the baby is now a little bit larger and we can do a detailed examination of the baby's anatomical structures, make sure that we don't see any sort of missing structures, additional structures, congenital defects, or things of that nature.

Now, ultrasounds can be abdominal, meaning that they're done on the abdomen, and this is usually in later pregnancy, usually at least 10 weeks gestation and up.

And then there is transvaginal, which is done using a transducer which is actually placed into the patient's vagina. Now, this is most commonly done to examine the cervix in later pregnancy or in early pregnancy to get a good look at the developing fetus because it's very small and that uterus has not fully lifted up out of the pelvic cavity. So important patient teaching here is that for a transvaginal ultrasound, you don't need to have a full bladder. However, with a transabdominal ultrasound, we would encourage our patient to have a full bladder because that full bladder will actually help to better reflect those sound waves. So important things to tell your patient before their appointments.

So moving on, we're going to talk about chorionic villus sampling, CVS. Now, the chorionic villus is that part of the-- villus means fingers, and chorion is a part of the structure of the developing placenta. So chorionic villus are the finger-like projections of the chorion. And this is a really good place to sample in early pregnancy between 10 to 13 weeks to diagnose genetic conditions. Now, this is invasive, so it actually involves passing a catheter through the cervix into the uterus and does put the patient at risk for complications like infection or even miscarriage. So very important to weigh the risks and benefits before doing this procedure. Now, like I said, it is between 10 and 13 weeks for early pregnancy, so this is not something that we would typically see done later on in pregnancy. Now, remember that because of the risk of bleeding, if your patient is Rh negative, then they should be receiving RhoGAM after the procedure to help to prevent any complications should there be mixing of maternal and fetal blood.

Okay. Now, another procedure that we can do for genetic testing is an amniocentesis. So if you remember, centesis is sampling or removing of a fluid from a cavity. So amnio is amniotic fluid. We're removing fluid from the amnion from the sac surrounding the baby, where there is that cushioning fluid. And in that fluid, we can take a sample and send it off for testing. So why would I do a chorionic villus sampling or an amniocentesis? I would do it if I have a strong family or personal history of a genetic condition that I need to know if my child is going to have. If I had early, what we call, cell-free fetal DNA testing. It's this blood test that a mom may have to see about genetic abnormalities with the fetus. If we see that there is a chance of a genetic abnormality, this would be the confirmation. We would have to actually get one of these tests to confirm it. So then you may also remember, we talked about the AFP, the maternal serum alpha-fetoprotein. This is another one that could be suggestive of a DNA abnormality, and this would be something that the patient could do to confirm. Now, the amniocentesis is done later on in pregnancy, so this is going to be between 15 to 18 weeks, and this actually involves passing a needle through the patient's abdomen, into the uterus, into the amniotic sac, and removing a small amount of fluid. So I want you to pause the video right now and tell me what do you think are going to be some concerns that you might have in doing this procedure.

Okay. I hope you paused the video. So any time I'm introducing something into a cavity, I'm at risk for infection, right? But I'm also really concerned about damage to the fetus, right? I'm putting a needle into the amniotic sac that protects the fetus. I'm worried about harming that baby. So this is done under ultrasound guidance. So it's not just done blindly. They can actually see where the baby is and where the needle is, but there's always that risk. There's also the risk that this could cause the rupture of membranes leading to amniotic fluid loss or leakage. This could cause miscarriage or fetal death as well. Same thing here, though, that we would want to give RhoGAM to an Rh-negative patient to prevent any possible complications from this, if that baby were to be Rh positive.

So we talked about a couple of things here: ultrasound, CVS, and amniotic fluid sampling, amniocentesis. I hope this review was helpful for you. If it was, it would mean the world to me if you could like this video. If you have a better way to remember something, I want to hear it in the comments below. Please tell me, and I know that other people watching this video do, too. Be sure that you subscribe to the channel so that you are the first to know when we have new videos in this series. Thanks so much and happy studying.

When I was pregnant with my daughter, I went for the anatomy scan, and we went in there and you could see her in profile. She was actually swallowing the amniotic fluid, and you could see her doing that. And this is something that babies do. They do breathe in and swallow the amniotic fluid and then they urinate it out. And that helps to get their kidneys functioning and helps them to practice breathing. But I have this really cool video of her swallowing amniotic fluid, and you could just see her little face so perfectly as she did it. It was really neat. It's incredible what you can see in these, nowadays.

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