12 Week NT Ultrasound

Between 11 and 13 weeks, it is very likely you will be sent for an ultrasound. The 12 week ultrasound is usually a lot of fun for the parents since babies tend to be active and photogenic. Parents are almost always in awe that the baby is already fully formed and there is a lot of kicking, jumping, and waving going on, even though the mother can’t feel it yet. By 12 weeks, the brain and other organs still need to grow and mature, but the baby is completely recognizable as a human with all the parts in place; skull, head, arms, legs, fingers, toes, liver, heart, stomach, bladder etc. Even though everything is there, it is tiny so a full in-depth analysis of all the organs and body parts will still need to be done at 18 to 20 weeks. Click here for more information on the 18 to 20 week ultrasound.

The baby’s anatomy will be briefly examined but the main purpose of the 12 week ultrasound is to take a measurement of the Nuchal Translucency or NT. The NT is a small collection of fluid that lies just under the skin at the back of the baby’s neck. This is usually well visualized with ultrasound and is measured to the nearest 100th of a centimeter. In order to do this test, sonographers and doctors need to be specially trained and certified. If it is thickened, that can indicate that the baby might have Down’s Syndrome or another chromosomal abnormality. It is not fully understood why the NT thickens in these babies, but it is probable that it is due to aberrations in development of the lymphatic system and tissues in chromosomally abnormal babies. However, plenty of babies with thickened NT’s are perfectly normal so DO NOT PANIC if your baby is found to have a thickened NT! However, it does mean that you will be offered further investigation with amniocentesisor CVS (click for more information), as well as additional monitoring as the pregnancy progresses.

The cutoff for normal NT thickness is generally 3 mm. If it is thicker than that, there is cause for concern, But again, most of the time, the good news is that most babies with a mildly thickened NT will be found with further testing to have normal chromosomes! But these babies are not out of the woods yet—some of these babies have a thickened NT because of a heart defect, cystic neck mass, or other anatomical problems. You will need follow up with serial ultrasounds and a targeted ultrasound of the fetal heart (a fetal echocardiography) to be sure that there is nothing else to be concerned about.

 

 

 

 

 

NT and First Trimester Screening: The NT measurement is taken to the nearest 100th of a centimeter. This number is sent to the lab performing the First Trimester Screening along with an ultrasound measurement of the length of the baby from crown to rump (which confirms the age of the fetus). Using sophisticated multivariate statistical formulas, the lab crunches the value of the NT measurement along with some values from a blood sample from the mother and her age at delivery to arrive at a risk estimate of Down’s or other common chromosomal problems. For more information on First Trimester Screening, click here.

Can you tell the gender at this scan? Boys and girls both have external genitalia at this point so it is not easy to tell gender yet. Every once in a while, by looking at the direction that the external phallus lies, the doctor or sonographer may feel confident enough to make a prediction. Don’t get too excited and buy blue clothes or paint the room pink yet!!! Predicting sex at this point is fraught with risk and many times, families are told what they thought was a boy turns out to be a girl (or vise versa) at the 18 to 20 week scan. You CAN tell the gender with near-perfection at the later scan. 12 weeks is just a bit too early to be sure. For more on gender determination, click here.

Can I get 3D/4D ultrasound at 12 weeks? 3D and 4D (4D is just 3D over time—see 3D/4D for more information) can be done at any point in a pregnancy and it can be really amazing at 12 weeks. But, because it is still a fetus and not a cute, chubby baby yet, it can look like a grasshopper or alien. Remember that 3D and 4D are computer generated images and while they can be fun, they shouldn’t be taken too literally.

If I refuse the screening for Down’s syndrome, do I still need a 12 week ultrasound? Of course, all testing and screening tests are optional. Many times, your doctor or midwife will encourage you to have the 12 week scan whether or not you decide to do the First Trimester Screening (see First Trimester Screening) since a thickened NT can also signal that there could be some anatomical defects present, especially with the heart. Studies repeatedly show that IF cardiac and other defects are found before birth, good outcomes are more likely. Babies with problems can be delivered at specialty centers with a team of doctors and professionals ready and prepared to provide the necessary support to maximize survival rates and successful corrections.

Comments

  1. ambrea long says:

    oh my gosh this helped me so much, i am 13 weeks pregnant and i have a huge fear that my baby will be born with downsyndrome. This information helped a lot!

    • Thank you so much for your comment, I have been working very hard on this site and am thrilled to hear that someone ‘out there’ has found it helpful. I am hoping to grow the ‘blogging’ part and hope you and others will freely post dialogue, ask questions, and give feedback. Feel free to contribute any time, and please tell any of your friends about the site (‘liking’ it on Facebook would help drive traffic and hopefully get discussions going!). Again, I really appreciate your feedback, and most of all, hope you enjoy a happy and healthy pregnancy & baby– Best wishes!

  2. Just had my scan yesterday at 12 weeks. This eased my mind a lot! There is a ton of info all condensed here, which makes things easier for a worried mama! Thank you so much again

    • Thanks Sonni! I am so glad you found the information helpful. Don’t hesitate to post a question or comment anytime. I also have a facebook page: PregnancyPro. You can ‘like’ me, and/or post questions there as well. All the best!

  3. Thank you for such great information!
    I had to persuade my doctor to let me do the test at 11wk 6 days (they normally said they want to wait until a few days after 12 weeks) but I am moving and will miss the window for getting it done before the 13 weeks is up. My appointment is late afternoon so i’m hoping it will be able to work. Do you know anyone who’s had it a day early and it worked for them? Thanks again for your info!

    • Hi Jamie,
      Don’t worry, 11 wks 6 days should be just fine. To be technical, all the labs who process the data are not interested in exactly how many weeks/days you are, but require that the embryo measures between 45 and 84 mm from head to rump, which corresponds to approximately 11 weeks 4 days and 13 weeks 5 days. Many ultrasound places like to aim for the 12 week mark as the minimum for scheduling only because if you unexpectedly a few days less or more pregnant than you think (it happens! a lot!), you won’t have wasted an appointment. As a matter of fact, just today I scanned someone who was only 11W1D from their period and much to my surprise, the embryo measured 48 mm, so I was able to submit all the data and get a good result.

      So, at 11W6D, you should be just fine. And don’t worry, it is VERY common that patients have to push the timing of the test for various reasons, the staff won’t be upset with you-they are used to it. Worst case scenario, your baby is smaller than 45 mm and they can’t do the test- that means you will have 2 full weeks to get it repeated. Usually, we don’t bother to even charge for the appointment time if you are rescheduled, but since you are moving, they may feel necessary to bill for the scan. I realize that’s not optimal for you, moving is an expensive thing, but hopefully they would cut you a deal. And don’t worry, you can get it done wherever you are moving to (unless it’s somewhere really exotic? ;) Best of luck, let me know how it goes!!

  4. Katrina Finley says:

    Thanks for the condensed version. We did a FET cycle to get pregnant (our last attempt). Currently we are 9w3d. We got to see our little jelly bean wiggle today on ultrasound. :)
    My worries are usual, of course….we aren’t wanting to do a cvs or an amino. To scared to disturb the sac. Is the NT reliable? Our babies were harvested at maternal age 34. Implanted at age 40. All chromosomes prior to pregnancy have been normal. :)

    • Hi Katrina, congratulations!!! Great news, getting to the 9w3D mark with a heartbeat and wiggling ;) is a HUGE hurdle. Regarding the reliability of the NT, just looking at the NT result by itself is not very reliable (about 65%). However, NT as part of the comprehensive 1st Trimester Screening where the lab combines values within your blood, the NT, and your age to decide whether or not you are low or high risk is quite reliable. It will catch approximately 88 to 95 out of every 100 abnormal babies. Those are quite good odds! The comprehensive test is more fully described in my post http://www.prenatalanswers.com/first-trimester-screening-for-downs-syndrome/ An approximately 90% accuracy rate in finding babies with Down’s Syndrome is great, but it does leave a little wiggle room for error. It’s a very personal choice for you whether living with a small margin of error is better or worse than taking the small but real risk of CVS/Amnio (which gives you 100% accuracy). Technically, you are low risk (i.e. amnio/CVS isn’t necessarily medically indicated) despite the fact that you are now 40 since your eggs were harvested at 34 years old. This fact can be calculated into the screening by the lab so as to give you the most accurate result. Your doctor or provider should be able to arrange that testing for you and best explain your specific risks. Many women who are on the fence about invasive testing will do 1st Trimester Screening and then factor in those results to make a final decision. Good luck!!

  5. What happens if I miss my window to have the NT ultrasound done? Thanks

    • The NT window is between 11.5 and 13.6 wks. If you missed it, then you can have additional bloodwork screening added to the 16 week blood test which will catch about 80 to 85% of babies with Downs Syndrome. This is slightly less accurate than the NT/1st trimester screening bloodwork, but still a good test. You will most likely be having a 16 week blood test anyway to test for elevated AFP (alpha fetoprotein) in your blood, which can be an indicator for spina bifida (see http://www.prenatalanswers.com/16-week-maternal-serum-afp-testing/). Your doctor or midwife will certainly know how to order the additional screening test onto the AFP since it was performed routinely before the NT/1st trimester screen replaced it. Again, it’s not quite as accurate as the NT/1st trimester screen, but it is a good test and was the gold standard for many years in testing for Downs Syndrome. IF you are high risk (i.e. over 35 or have a history of concern) you can of course opt to have an amniocentesis, or consider the newer non-invasive maternal serum screening such as the MaterniT21 or Verify tests. These are not standard of care as of yet, but are becoming the test-of-choice in higher risk families over amniocentesis. Information on both tests are available on this site: see http://www.prenatalanswers.com/amniocentesis/ and http://www.prenatalanswers.com/new-non-invasive-blood-test-that-can-detect-downs-syndrome-in-pregnancy/

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