First-Trimester Screening Ultrasound in Ajax: An Overview

Is it a test that tells you whether something is wrong, or a test that tells you how likely it is? That one question sits at the heart of first-trimester prenatal screening, and it is the one most worth understanding before you decide whether screening is for you.

Many expecting parents in Ajax, Pickering and Whitby first hear about prenatal screening at an early prenatal visit, often alongside a long list of other new information: due dates, blood work, vitamins, what to eat and what to avoid. It is easy for screening to blur into the routine. But it is different from most other early pregnancy care in one important way. It is optional, and the choice about whether to have it belongs to you.

This overview explains, in general terms, what first-trimester screening usually involves, how the ultrasound part fits in, what a screening result can and cannot tell you, and which questions are worth bringing to your provider. It deliberately does not repeat our posts on the first early pregnancy scan or the dating ultrasound, which cover those appointments in detail. Please read it as background, not as medical advice; your doctor or midwife is the right person to guide decisions for your pregnancy.

Screening and diagnosis are not the same thing

The single most useful idea to hold on to is the difference between these two words.

A screening test estimates the chance that a pregnancy is affected by certain conditions. It does not give a yes or no answer. A screening result is usually described as a lower chance or a higher chance, sometimes with a number attached. A higher-chance result does not mean the baby has the condition, and a lower-chance result does not rule out every possible condition.

A diagnostic test aims to give a definite answer about a specific condition. In pregnancy, diagnostic tests generally involve sampling cells from the placenta or the fluid around the baby. They are offered when there is a specific reason, such as a higher-chance screening result, and they carry their own considerations, which a provider or genetic counsellor discusses in detail.

Screening is often described as a first step that helps some families decide whether they want to consider diagnostic testing. For many families, it is also the last step, because the result is reassuring enough that they choose to go no further.

What first-trimester screening usually looks for

In general, prenatal screening is designed to estimate the chance of certain chromosomal conditions, such as Down syndrome (trisomy 21) and some others. Depending on the type of screening, it may also flag findings that lead a provider to suggest closer follow-up.

The precise list of conditions depends on the screening method. That is one of the things worth asking your provider, because “screening” can mean slightly different packages of tests.

The ultrasound part: what is being measured

When people talk about a first-trimester screening ultrasound, they are usually referring to a scan that includes a nuchal translucency (NT) measurement. “Nuchal” refers to the back of the neck. In the developing baby there is a small, fluid-filled space under the skin at the back of the neck, and on ultrasound it appears as a thin dark band. The sonographer measures the thickness of that band.

A few points help to understand why this measurement is handled so carefully:

• The timing window is narrow. NT measurement is generally done between about 11 and 14 weeks of pregnancy. Before and after that window the measurement is not used in the same way. This is one reason accurate dating matters.
• Technique matters. The measurement is tiny, and the baby must be in the right position, at the right magnification and in the right plane. Sonographers who perform NT measurements for screening programs typically need specific training and certification.
• The number is one ingredient, not the result. The NT measurement is usually combined with other information, such as blood test results and the age of the person who is pregnant, to calculate a screening result. On its own, the measurement does not give you an answer.

During the same scan, the sonographer will typically confirm the number of babies, check the heartbeat and take measurements that relate to how far along the pregnancy is.

Does Rossland Diagnostic Clinic offer NT screening?

Not every ultrasound clinic performs nuchal translucency measurements for prenatal screening, because of the specialized certification involved. If you are looking for an NT scan, ask your health-care provider where they recommend you go, and call us at 905-426-3111 to confirm whether this particular exam is available at our Ajax location before you book. We would rather you get the right appointment the first time.

The blood test part

In Ontario, a commonly offered first-trimester option combines the NT ultrasound with a blood test from the pregnant person. The blood test measures substances made by the pregnancy and placenta. The ultrasound measurement and blood results are then combined to estimate a screening result.

There is also a type of screening that analyses small fragments of DNA from the placenta circulating in the pregnant person’s blood. It is often called cell-free DNA screening or non-invasive prenatal testing. It is still a screening test, not a diagnostic one, and it is offered differently depending on individual circumstances. Your provider can explain which options are available to you and how each one works, including any costs or eligibility questions, which we cannot advise on.

How the timing fits around other early scans

Early pregnancy can involve more than one ultrasound, and people sometimes wonder which is which. Very broadly:

1. An early or dating scan, if your provider orders one, helps confirm the pregnancy and estimate how far along it is.
2. A screening ultrasound with NT measurement, if you choose screening that includes it, happens in the window around 11 to 14 weeks.
3. A detailed anatomy scan is usually done later, around the middle of pregnancy. Our post on the mid-pregnancy anatomy scan explains it.

In some pregnancies, a single early ultrasound can serve more than one purpose. Your provider will arrange what is appropriate, so there is no need to work out the sequence yourself. For a bigger picture of how scans are spread across pregnancy, see our trimester-by-trimester guide.

What the appointment can feel like

A screening ultrasound in the first trimester is usually done across the abdomen, using gel and a handheld probe. Because the baby is small and the measurement is precise, it can take some time. The sonographer may ask you to cough, shift position or walk around briefly to encourage the baby to move into a better position. Occasionally, a transvaginal scan is suggested if the view from the abdomen is not clear enough; you can always ask questions and you can always say no.

Preparation instructions, including whether you need a comfortably full bladder, are given at booking and can vary, so follow the instructions you receive. Bring your health card and the requisition from your provider.

It is also normal for the sonographer to say relatively little about the measurement during the scan. The result is calculated as part of a process that combines several pieces of information, and it is shared with your health-care provider.

Receiving a result

Screening results usually go to the provider who ordered the screening, who then shares them with you. Ask your provider in advance how and when you can expect to hear, so that you are not left waiting by the phone wondering. Our general article on how imaging results reach your doctor explains the reporting pathway for ultrasound.

If a result shows a lower chance, many families feel reassured and continue routine care. If a result shows a higher chance, your provider will explain what it means for your pregnancy and what options are available, which may include further screening, a referral to genetic counselling or the offer of a diagnostic test. A higher-chance result is not a diagnosis, and you have time to ask questions and think.

Deciding whether screening is right for you

Some people know immediately that they want every piece of information available. Others feel strongly that they do not want screening. Many sit somewhere in between. All of these are reasonable positions.

Questions that can help you think it through:

• What would I do with the information? Some people want to prepare emotionally or practically. Others want to consider diagnostic testing if the chance is higher. Some would not change anything.
• How do I feel about uncertainty? A screening result is a probability. Some people find that reassuring; others find it adds worry.
• What options are available to me? Ask your provider which screening methods are offered, what each one looks for, and how accurate each is considered to be.
• Who do I want to talk it over with? A partner, a family member or a genetic counsellor can all help.

Whatever you decide, routine prenatal care continues, and the other ultrasounds your provider recommends can still be booked close to home in Ajax.

Symptoms that should not wait for any scan

Screening appointments are scheduled tests. They are not the place to bring urgent symptoms. Call 911 or go to the nearest emergency department if you have heavy vaginal bleeding, severe abdominal or shoulder-tip pain, fainting or feeling very faint, chest pain or trouble breathing. For lighter bleeding, cramping or anything else that worries you, contact your doctor or midwife promptly rather than waiting for your next appointment. A community imaging clinic is not set up to provide emergency care.

Pregnancy imaging close to home

Rossland Diagnostic Clinic provides obstetrical and general ultrasound for patients from across Ajax and Durham Region, with free parking, ground-floor access and Saturday hours from 8:00am to 3:30pm as well as weekday hours from 9:00am to 5:00pm. If your provider has given you a requisition for a pregnancy ultrasound, or you would like to confirm which exams we can offer before you book, call 905-426-3111 or request an appointment. Our team will help you sort out the details.