First-trimester ultrasound: what is usually checked
The first-trimester ultrasound is, for many families, a much-awaited moment. It is usually the first time the baby is seen clearly and, at the same time, an important assessment to follow the early stages of pregnancy.
Besides bringing emotion and relief, this scan gives the doctor useful information about how the pregnancy is progressing. In Portugal, it can be done in the public health system or privately, and it usually forms part of standard antenatal care. The aim is to confirm that the pregnancy is developing as expected and to look for signs that may need extra monitoring.
This article explains, in simple terms, what is usually checked, when the scan is done, and what each finding may mean.
What is the first-trimester ultrasound?
It is an ultrasound scan usually performed between 11 weeks and 13 weeks and 6 days of pregnancy. At this stage, the baby is still very small, but it is already possible to see several important details of development.
In many cases, this scan is part of the first-trimester screening. In addition to showing the baby, it may include specific measurements that help assess the risk of certain chromosome conditions and confirm whether the pregnancy is progressing as expected.
When is it usually done?
The most common time is between 11 and 14 weeks of pregnancy. Before that, some structures may not yet be developed enough for a complete assessment. After that window, some measurements are less reliable.
If there is pain, bleeding, suspected ectopic pregnancy, or other clinical concerns, the doctor may request an earlier ultrasound. In those cases, the scan has a different purpose and does not replace the first-trimester ultrasound.
What is usually checked?
1. Confirmation that the pregnancy is in the uterus
One of the first things checked is whether the pregnancy is located inside the uterus. This is important to confirm that it is an intrauterine pregnancy and not an ectopic pregnancy, which occurs outside the uterus and requires urgent care.
2. Number of embryos or fetuses
The ultrasound shows whether it is a singleton or twin pregnancy. When there is more than one baby, the doctor may assess whether they share a placenta and amniotic sac, which helps plan follow-up.
3. Gestational age and estimated due date
One of the most important roles of the first-trimester ultrasound is confirming gestational age. At this stage, the embryo’s measurement is usually quite accurate and can be used to estimate the due date.
This is especially useful when the date of the last menstrual period is uncertain, periods are irregular, or there is any doubt about how the pregnancy is developing.
4. Heartbeat
The doctor checks whether there is embryonic or fetal cardiac activity. The presence of a heartbeat is an important sign that the pregnancy is progressing at that moment.
It is important to remember that, this early on, the heartbeat may not yet be visible in every situation, depending on gestational age and image quality.
5. Baby’s growth and size
The ultrasound usually measures crown-rump length, also called CRL. This measurement helps assess whether growth is in line with the pregnancy stage.
If there is a meaningful difference between the calculated gestational age and the observed size, the doctor may want to repeat the scan or keep a closer watch.
6. Early anatomy
Although the baby is still at a very early stage, the doctor can already observe some basic structures, such as the head, trunk, developing limbs, and abdominal wall.
The goal is not yet to see the full anatomy in detail, but to check for early signs of expected development and whether there is any finding that needs special attention.
7. Nuchal translucency
This is one of the best-known measurements in this scan. Nuchal translucency is a small fluid collection at the back of the baby’s neck, measured within a very specific pregnancy window.
When included in first-trimester screening, this measurement can help estimate the risk of certain chromosome conditions, such as trisomy 21, 18, and 13, together with other factors such as the mother’s age and blood tests.
An increased measurement does not, on its own, mean there is a problem. It only indicates that further assessment with other tests may be needed.
8. Nasal bone and other markers
In some cases, the doctor also looks at the nasal bone and other ultrasound signs that may be part of combined first-trimester screening. These findings should always be interpreted together with the broader clinical picture.
9. Uterus, ovaries, and placenta
The ultrasound can also assess the mother. The professional looks at the uterus, ovaries, and, when possible, the position of the placenta. This helps identify conditions such as fibroids, cysts, uterine changes, or placental implantation that may need monitoring.
What can a normal result mean?
A result without relevant abnormalities usually brings reassurance, but it does not remove all risks throughout pregnancy. It simply means that, at that stage, the development seen was in line with expectations and no warning signs were seen in that scan.
Even with a normal ultrasound, ongoing check-ups, routine tests, and the follow-up recommended by the obstetrician, family doctor, or maternity care team remain important.
When might the ultrasound need to be repeated?
The doctor may ask for another ultrasound if the image is not clear enough, if gestational age is uncertain, if there are doubts about the heartbeat, or if a finding needs confirmation.
It may also need to be repeated when there are symptoms such as abdominal pain, bleeding, or when the pregnancy is considered higher risk.
How should you prepare for the ultrasound?
In most cases, no special preparation is needed. Even so, it is worth following the instructions from the health unit, because some services may ask for a full bladder in earlier ultrasounds or certain types of scan.
Bringing previous test results, the date of the last menstrual period, and any information about fertility treatment, if applicable, can help the professional interpret the situation more accurately.
What do parents often feel at this time?
The first-trimester ultrasound can bring very strong emotions. For some families, it is a moment of joy and connection with the baby. For others, it may be experienced with anxiety, especially after previous losses, fertility treatment, or a higher-risk pregnancy.
It is natural to leave the appointment with many questions. If something is not clear, it is worth asking for an explanation. No question is too small when it comes to your baby’s health and your family’s peace of mind.
When should you seek urgent medical help?
Seek urgent medical assessment if there is heavy bleeding, severe pain, dizziness, fainting, fever, or fluid loss. These symptoms do not always mean something serious, but they need prompt attention.
If the ultrasound shows something unexpected, the doctor will explain the next step. In many cases, the recommendation is simply to repeat the scan later or to do additional tests.
Helpful questions to ask the doctor
If you want to make the most of the appointment, you can ask:
- How many weeks pregnant am I according to the ultrasound?
- Is the heartbeat within the expected range?
- Is the nuchal translucency normal?
- Is there any sign that needs extra monitoring?
- When should I come back for the next ultrasound?
- Do I need any additional tests?
In summary
The first-trimester ultrasound is a very important exam at the start of pregnancy. It usually checks the location of the pregnancy, the number of babies, gestational age, the heartbeat, early growth, and some markers used in screening for chromosome conditions.
At the same time, it is a chance for parents to better understand how the pregnancy is progressing and to receive appropriate medical guidance. If there are doubts, symptoms, or unclear results, the most important thing is to keep follow-up appointments and ask the health team for explanations.
Clear information helps make this moment feel calmer and more reassuring.
