Screening for Down Syndrome
People with Down Syndrome have physical and intellectual disabilities. Older women have a greater chance of having a baby with Down Syndrome.
When a woman is around 12 weeks pregnant, her chance of having a baby with Down Syndrome can be accurately assessed. First trimester screening for Down Syndrome can be done with a blood test between 10 weeks and 13 weeks and 6 days. When a fetus has Down Syndrome, they tend to have more fluid at the base of their neck, in the region known as the nuchal fold area. This fluid can be measured in a test called nuchal translucency. This can be measured in an ultrasound done between 11 weeks and 13 weeks and 6 days. A fetus with Down Syndrome has a measurement that is thicker than in those who do not.
It is worth remembering though, that a larger than average nuchal fold measurement is not a guarantee that the baby will have chromosomal problems. Other tests for Down Syndrome need to be done if in doubt. In addition, tests such as a chorionic villus sampling test or an amniocentesis help to clarify any suspicions.
Spotting other complications
Parents need to feel as if they are fully informed and comfortable with the explanations provided by the sonographer doing the 12 week ultrasound. Follow up care by the healthcare team is equally important. It is common for ultrasounds to be repeated and reviewed if there are any concerns.
First trimester screening tests
How a 12 week ultrasound is performed
Reasons to have a 12 week ultrasound
- To check that the fetus is developing as it should be. The measurement of the fetus's skull—the biparietal distance—is calculated and compared against standard lengths for fetuses at similar gestational ages.
- To see if the fetus has a heartbeat. This should be clearly detectable at the 12 week ultrasound.
- To confirm pregnancy dates and estimate the date of delivery.
- To check for multiple fetuses and confirm if one or more is present.
- To check the size of the fetus and developing placenta.
- To measure the amount of fluid at the base of the fetus's neck which is called the nuchal translucency. This is used for the individualized assessment for Down Syndrome. The sound waves from the ultrasound return echo-free measurements. This is because of the space which is translucent due to its fluid content.
- To check for other physical abnormalities in the fetus.
- To check the uterus, fallopian tubes and pelvic region for other complications.
Other measurements taken at the 12 week ultrasound
- The fetus's length, specifically from its head to its bottom. This is known as a crown rump length.
- A general check of the mother and fetus's internal organs and structures.
Many parents feel an instant emotional connection with their baby when they see it for the first time. It's not uncommon for partners to say that until the 12 week ultrasound, the whole pregnancy idea was a little foreign and somehow not real. Being able to see their baby rather than talking about it and having to use their imagination can make all the difference.
When will I know if everything's alright with my 12-week ultrasound?
The sonographer will be able talk their way through the procedure and turn the screen so that you can see what they are looking at during the ultrasound. There may also be a separate monitor for you and your partner to look at. If you want explanations, ask the sonographer to tell you what they are checking.
If they are unsure or want clarification, they will often request a colleague come into the room and have a look at the ultrasound. This can be a pretty unnerving process especially if you've not had any reason to believe that there are any complications.
How accurate is the first trimester screening test?
Having a low chance result for the first trimester screening test does not give a 100% guarantee that there will not be a chromosomal abnormality. What it does is categorize a pregnancy into an increased or decreased chance.
How long will my 12-week ultrasound take?
Put aside some time before and after your ultrasound so you can make it to the appointment in plenty of time and have the chance to reflect on it afterwards. Ask your partner to be with you on the day and aim to enjoy this as an event you can both share.
Are 12-week ultrasounds part of my routine pregnancy care?
Some parents feel very strongly that having an ultrasound is not right for them. Part of their reasoning is that if abnormalities are found, then they may be put into a position of having to make decisions based on these findings. This is understandable and up to each parent to decide for themselves.
Some parents choose to wait until the screening ultrasound at 18 to 20 weeks and feel that at 12 weeks it is still too early to be able to see much of their baby's development. If you are in any doubt, speak with your maternity care provider about your preferences.
The information of this article has been reviewed by nursing experts of the Association of Women’s Health, Obstetric, & Neonatal Nurses (AWHONN). The content should not substitute medical advice from your personal healthcare provider. Please consult your healthcare provider for recommendations/diagnosis or treatment. For more advice from AWHONN nurses, visit Healthy Mom&Baby at health4mom.org.