Screening for Down Syndrome During Pregnancy: What You Need to Know

Highlights

• Down syndrome is a common genetic (chromosomal) disorder that leads to intellectual disability.
• You can have a screening test to find out if your baby is likely to be born with Down syndrome.
• Screening tests are usually done during the first trimester of pregnancy.
• Talk to your doctor or a genetic counselor to decide if screening is right for you.

In This Article

• Down Syndrome Overview
• Screening for Down Syndrome
• Reasons for Screening for Down Syndrome
• Preparing for Screening for Down Syndrome
• Methods of Screening for Down Syndrome
• Cost of Screening for Down Syndrome
• Understanding Screening Test Results
• Diagnostic Tests for Down Syndrome
• Optional Nature of Down Syndrome Screening
• Questions for Your Midwife or Doctor
• Tools and Assistance

Down Syndrome Overview

Down syndrome is a common genetic (chromosomal) condition that causes mild to moderate intellectual disability. People with Down syndrome may have distinct physical features and some additional health concerns.

Most people have 23 pairs of chromosomes in every cell of their body. Individuals with Down syndrome have an extra chromosome 21. This is why Down syndrome is also known as Trisomy 21.

Screening for Down Syndrome

There are several antenatal tests available to assess the health of a developing baby. Screening tests can help determine if a baby has an increased likelihood of being born with a chromosomal condition such as Down syndrome.

These tests include ultrasound scans and blood tests. However, a screening test does not diagnose Down syndrome but only estimates the probability of the condition.

Reasons for Screening for Down Syndrome

There is always a possibility that a baby may be born with a genetic or chromosomal condition. Screening tests provide parents with early information, allowing them to make informed choices about pregnancy and potential care options.

Screening results can help in:

• Planning for medical care and support after birth.
• Making decisions about additional diagnostic testing.
• Monitoring the pregnancy more closely if needed.

If screening results indicate an increased chance of Down syndrome, further testing will be offered to confirm the diagnosis.

Preparing for Screening for Down Syndrome

Before undergoing screening, it is important to consider why you are choosing to take the test and how you might feel about the results.

Discuss the available options with your doctor, midwife, or a genetic counselor.

Think about whom you would like to discuss your results with—your partner, a family member, or a close friend.

Ask your healthcare provider if any preparation is required before the test.

Methods of Screening for Down Syndrome

There are three primary screening methods for Down syndrome:

• Combined First Trimester Screening: This is the most common screening method and involves:
  • A blood test between week 10 and week 13 of pregnancy.
  • A nuchal translucency ultrasound scan between week 11 and week 14 of pregnancy.
  • The blood test measures two substances:
    • Pregnancy-associated plasma protein A (PAPP-A), which is made in the placenta.
    • Free beta human chorionic gonadotropin (free β-hCG), a pregnancy-related hormone.
  • These results, combined with the nuchal translucency measurement, along with maternal age and weight, estimate the likelihood of the baby having Down syndrome. This test detects about 85% to 90% of cases.
• Non-Invasive Prenatal Testing (NIPT): NIPT is a more advanced screening method that involves a blood test taken after 10 weeks of pregnancy. It analyzes fetal DNA circulating in the mother’s blood and is 99% accurate in detecting Down syndrome.
  • This test does not require an ultrasound but can be expensive.
• Second Trimester Serum Screening: If the first-trimester screening is missed, an alternative blood test can be taken between weeks 14 and 20 of pregnancy.
  • This test measures certain proteins and hormones in the mother’s blood and can detect about 75% of Down syndrome cases.

Cost of Screening for Down Syndrome

The cost of screening tests varies by location and healthcare provider. Some healthcare systems may cover part or all of the cost, while others may require out-of-pocket expenses.

The first-trimester blood test and ultrasound may have associated costs.

NIPT is typically more expensive than other screening methods.

Second-trimester screening may be more accessible but slightly less accurate.

It is best to consult with your healthcare provider to understand the financial aspects of each test.

Understanding Screening Test Results

Your doctor or midwife will explain your test results. Screening tests provide a probability rather than a definitive diagnosis.

• Low-risk result: Indicates that the baby is unlikely to have Down syndrome.
• High-risk result: Suggests a higher probability that the baby has Down syndrome, and further diagnostic testing may be recommended.

If a high-risk result is received, additional testing options and genetic counseling may be considered to discuss next steps.

Diagnostic Tests for Down Syndrome

If screening results indicate a high probability of Down syndrome, diagnostic tests can provide a definitive answer.

Diagnostic Tests Include:

• Chorionic Villus Sampling (CVS): A test performed between weeks 10 and 13 that examines placental tissue for chromosomal abnormalities.
• Amniocentesis: A test conducted after week 15 that analyzes amniotic fluid surrounding the baby.

After birth, a blood test can confirm the diagnosis of Down syndrome.

Optional Nature of Down Syndrome Screening

Screening for Down syndrome is entirely optional. It is a personal decision, and discussing the pros and cons with a healthcare provider can help determine whether screening is the right choice.

Questions for Your Midwife or Doctor

Here are some questions to consider asking your healthcare provider:

• Why are you offering me this test?
• What does the test involve?
• Do I need to prepare in any way for the test?
• When will I receive the results?
• Who will discuss the results with me?
• What are my options if the test results show a high probability of Down syndrome?

Tools and Assistance

Support organizations and genetic counselors provide valuable information and assistance for parents facing a Down syndrome diagnosis.

Support services may include:

• Information on Down syndrome and what to expect.
• Parental guidance and counseling.
• Resources for early intervention and medical care.

If you need further information, consult your doctor or midwife, who can guide you to the appropriate resources.

Need more information?

Maternal screening | Pathology Tests ExplainedThe maternal serum screening tests involve the measurement of different pregnancy-associated hormones, which are found in all pregnancies. Read more on Pathology Tests Explained websiteHealth Screening Tool – Down Syndrome AustraliaThis resource provides information on some of the more prevalent health conditions that people with Down syndrome may experience and the health screenings that should be made available.Read more on Down Syndrome Australia websiteSupport – Prenatal ScreeningPeople often contact our service to better understand their screening resultsRead more on Prenatal Screening – Down Syndrome Queensland websiteDSA Prenatal Testing Factsheet – Prenatal ScreeningSupport through the Down Syndrome Queensland support service is available for any prospective parent, health care professional, community service, carer or family members supporting someone who has received unexpected news about their pregnancyRead more on Prenatal Screening – Down Syndrome Queensland websitePrenatal Screening for Chromosomal and Genetic ConditionsOur genetic material, or DNA, is organised into 46 packages called chromosomes. Some people are born with too many or not enough chromosomes, which can affect their health and learning. Smaller changes in the DNA can also occur within a chromosome, resulting in a variety of genetic conditions.Read more on RANZCOG – Royal Australian and New Zealand College of Obstetricians and Gynaecologists websiteNon-invasive prenatal testing (NIPT)A non-invasive prenatal test (NIPT) is a sensitive test to screen for Down syndrome and some other chromosomal disorders early in pregnancy.Read more on Pregnancy, Birth & Baby websiteWhat it’s like to Receive an Unexpected Result – Prenatal ScreeningSupport through the Down Syndrome Queensland support service is available for any prospective parent, health care professional, community service, carer or family members supporting someone who has received unexpected news about their pregnancyRead more on Prenatal Screening – Down Syndrome Queensland websiteMaternity Consumer Network Patient Information Brochure – Prenatal ScreeningSupport through the Down Syndrome Queensland support service is available for any prospective parent, health care professional, community service, carer or family members supporting someone who has received unexpected news about their pregnancyRead more on Prenatal Screening – Down Syndrome Queensland websiteWhat is Down syndrome?Down syndrome is a condition caused by 3 copies of chromosome 21. People with Down syndrome may have physical and intellectual disabilities.Read more on Pregnancy, Birth & Baby websiteDown syndrome: babies, children & teens | Raising Children NetworkDown syndrome causes intellectual disability and other challenges. Early intervention can help children with Down syndrome reach their full potential.Read more on raisingchildren.net.au website