First Trimester Screening: Screening for Down Syndrome and More

Pregnancy is an exciting and joyful time, but it’s natural to feel anxious about your baby’s health. If you are in your first trimester, your doctor may have mentioned first-trimester screening as an early health assessment.

You may be wondering what it involves and whether it is suitable for you. To help you make an informed decision about your care during pregnancy, let's take a closer look at the screening process, when it is carried out and what the results mean.

What is first-trimester screening?

First-trimester screening serves as an early health assessment for both you and your baby. It is usually conducted when you are between 11 and 14 weeks pregnant. This screening is a crucial step to check for chromosomal abnormalities like Down syndrome, which can influence your baby's development. 

Simultaneously, it also provides an opportunity to ensure your baby is growing well and that your own health is on track, as certain conditions could negatively impact the pregnancy. 

What tests are recommended to be performed?

General health check

A general health check involves a consultation with your doctor, where they’ll review your medical history, lifestyle, blood pressure, weight, and any pre-existing conditions you may have. This allows them to identify any risk factors, such as high blood pressure or chronic illnesses, that could complicate your pregnancy. Your doctor may also discuss nutrition, exercise, and supplements such as folic acid to ensure the best possible start for your pregnancy.

Ultrasound dating scan

An ultrasound dating scan is usually carried out between 8 and 12 weeks of pregnancy to confirm your due date and to check the number of foetus. This scan also confirms that the pregnancy is located inside the uterus and that the baby has a heartbeat. 

During the first-trimester scan, the baby’s measurements, such as crown-rump length, are taken to provide the most accurate estimation of gestational age. This information is important for planning later antenatal tests and monitoring the baby’s growth.

Antenatal blood test

Routine blood tests are performed in early pregnancy to evaluate the mother’s general health and to detect any issues that may need attention. These typically include a full blood count to check for anaemia, blood group and Rh status, screening for infections such as HIV, hepatitis B, and syphilis, and sometimes tests for immunity to rubella or varicella. 

A urine test may also be performed to detect urinary tract infections or protein in the urine. These tests help ensure that any treatable conditions are addressed early in pregnancy.

Down syndrome screening

Specific screening for chromosomal abnormalities, including Down syndrome, Edwards syndrome, and Patau syndrome, is also offered in the first trimester. This often involves a combined test, which includes an ultrasound measurement of the fluid located at the back of the baby’s neck (nuchal translucency) and a blood test measuring pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG) levels. 

Together, these results provide an estimate of the baby’s risk for chromosomal abnormalities. More recently, non-invasive prenatal testing (NIPT), which looks at cell-free foetal DNA in the mother’s blood, has become available and offers higher accuracy.

When is this screening performed during pregnancy?

First-trimester screening is usually carried out between 11 weeks and 13 weeks plus 6 days of pregnancy. This specific timeframe is critical because the nuchal translucency (fluid at the back of the baby's neck) can only be accurately measured during this window – it becomes too difficult to visualise after 14 weeks.

Additionally, maternal blood hormone levels during this stage of pregnancy are most informative, helping to ensure that you receive a comprehensive understanding of your baby’s health.

Your baby’s growth during this time

During the first trimester, the baby grows rapidly from a small embryo into a foetus with recognisable features. By the end of this period, most of your baby’s vital organs have formed. The dating scan and first-trimester screening help to confirm that your baby is developing normally, with appropriate growth for the pregnancy age, ensuring that there are no major early abnormalities.

To schedule your first-trimester screening or discuss any concerns about your pregnancy, our experienced gynaecologists at Thomson Women's Clinic are here to help. Contact us to arrange a consultation and receive personalised care throughout your first trimester.

What to prepare for this screening?

First-trimester screening requires minimal preparation.  Here are a few tips to make your first visit easier and more comfortable:

• Gather your essentials:

  • Bring along your antenatal booklet and any previous medical records. This can help ensure that your healthcare provider has all the information needed. 

• Check imaging requirements:

  • Some clinics may recommend arriving with a partially full bladder, as it can enhance the quality of the ultrasound images. 

• Blood test preparations:

  • Generally, no fasting is required for blood tests during your screening unless your healthcare provider explicitly advises it. 

• List your medications and supplements:

  • Having a list of all the medications and supplements you are currently taking will be beneficial. Your doctor can review them to ensure that they are safe.

Being prepared for your appointment can help you feel more at ease and ensure that your screening is as smooth and informative as possible. Remember, your healthcare team is there to support you every step of the way.

During the screening

During the screening, your doctor will review your health, carry out the ultrasound scan, and draw blood samples from you if further tests are required. The ultrasound is painless and involves gliding a probe across your abdomen to visualise the baby. The process usually takes about 20-30 minutes, depending on your baby’s position and movement. 

The results will then be compiled to provide a comprehensive and informative assessment of the potential risk for chromosomal conditions, ensuring that you have the information needed to make informed decisions for your baby’s health.

What do the results mean?

The results from first-trimester screening offer an estimated risk of chromosomal abnormalities in the baby, rather than a definitive diagnosis. A "low-risk" result suggests that it is unlikely for your baby to have a chromosomal condition, whereas a "high-risk" outcome indicates that further testing might be recommended. 

In cases of high risk, your doctor could suggest more in-depth screenings, like non-invasive prenatal testing, or diagnostic procedures such as chorionic villus sampling or amniocentesis. Regardless of the results, your healthcare provider will clearly discuss what they mean and guide you through the next steps.

Have questions about your screening results? Our obstetrics and gynaecology specialists are here to clear your doubts. Request an appointment.

Are there any risks for this procedure?

First-trimester screening is typically safe and does not present any significant risks to either the mother or the baby.

The ultrasound procedure is non-invasive and harmless, while blood sampling involves only minimal risks, such as minor bruising or slight discomfort at the site of needle insertion. Importantly, the screening does not elevate the risk of miscarriage.

In cases where further diagnostic tests are suggested, like amniocentesis or chorionic villus sampling, there are minor risks involved, but the initial screening remains a safe and standard practice for expectant mothers.

FAQ

How to confirm your pregnancy in the first month?

Pregnancy in the first month can be confirmed through an at-home pregnancy test, which detects the presence of human chorionic gonadotropin (hCG), a hormone produced by the placenta shortly after implantation. These tests are widely available, simple to use, and can often detect pregnancy even a few days after a missed period. 

For greater accuracy, a blood test may be performed in a clinic to measure the exact level of hCG. An early ultrasound is not usually helpful in the first month, since the pregnancy may be too small to visualise, but by around 5–6 weeks, an ultrasound can confirm the presence of a pregnancy sac in the uterus.

What tests are done in first-trimester screening?

First-trimester screening usually includes a combination of maternal blood tests and an ultrasound scan. The blood tests measure specific pregnancy-related hormones, such as pregnancy-associated plasma protein A (PAPP-A) and human chorionic gonadotropin (hCG), which can be altered in pregnancies affected by chromosomal abnormalities. 

The ultrasound involves measuring the nuchal translucency, which is the fluid at the back of the baby’s neck, as well as checking the baby’s anatomy, heart rate, and growth. Together, these results are used to estimate the risk of conditions such as Down syndrome, Edwards syndrome, and Patau syndrome.

How soon can you do first-trimester screening?

First-trimester screening is typically performed between 11 weeks and 13 weeks plus 6 days of pregnancy. This time frame is important because the baby must be developed enough to allow accurate ultrasound measurements, especially of the nuchal translucency. If the test is done too early, the measurements may not be reliable, and if it is done after 14 weeks, the screening window is considered missed.

Is 12 weeks too late for the first prenatal visit?

Twelve weeks is not too late for the first prenatal visit, but ideally, it is best to book an appointment as soon as pregnancy is confirmed. Early prenatal visits are important to establish gestational age, review maternal health, start necessary supplements like folic acid, and perform initial blood tests. 

If the first visit occurs at 12 weeks, most essential checks, including the first-trimester screening, can still be completed within the recommended time frame. However, delaying beyond this point may result in missed opportunities to detect certain conditions early.

What are early signs of Down syndrome in pregnancy?

Down syndrome does not usually present with obvious physical signs during early pregnancy that a mother can feel or notice. Instead, potential markers may be detected through ultrasound or blood tests. On ultrasound, increased nuchal translucency thickness, absence of the nasal bone, or certain heart and organ findings may raise suspicion. 

Blood test results showing abnormal levels of PAPP-A or hCG may also suggest a higher risk. These are only screening indicators, not definitive signs, and further testing is required to confirm the diagnosis.

What happens if you miss first-trimester screening?

If you miss the first-trimester screening, you still have other opportunities to assess the baby's health. A second-trimester screening, often called the “quadruple test”, can be performed between 15 and 20 weeks to estimate the risk of chromosomal abnormalities. Detailed anomaly scans around 18–22 weeks can also help detect structural abnormalities. 

In addition, non-invasive prenatal testing (NIPT) provides a highly accurate assessment of chromosomal conditions and can be done at almost any point after 10 weeks. While missing the first-trimester screening may limit some early diagnostic options, there are still effective alternatives later in pregnancy.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations and tailored advice, please consult a specialist at Thomson Medical. Request an appointment with Thomson Medical.