Pregnancy - tests and scans

A range of tests and scans are an important part of pregnancy care. They can confirm a pregnancy, monitor the health of you and your baby, and provide information about whether a pregnancy is affected by certain conditions. Your doctor or midwife can explain what tests are available and which ones may be useful for you.

The tests available to pregnant women generally fall into a few groups: tests to confirm pregnancy, routine prenatal tests to monitor health, and tests for specific medical conditions (screening and diagnostic tests).

Confirming a pregnancy#

A missed menstrual period is often the first sign of pregnancy.

Tests that confirm pregnancy detect a hormone called human chorionic gonadotropin (βhCG). Options include:

• Home test kits, available from pharmacies. A typical kit includes special paper that reacts to βhCG in urine. It is important to follow the manufacturer’s instructions carefully, because incorrect use can give false results.
• A urine test done by your doctor.
• A blood test, which measures βhCG levels and can be accurate within about a week of conception.

Pregnancy tests done by your doctor are rarely inaccurate, so it is a good idea to confirm a home test result with your doctor.

Routine prenatal tests#

Once a pregnancy is confirmed, care involves regular appointments with your doctor or midwife to monitor the pregnancy and your baby’s growth. Routine tests check the health of both you and your baby and help identify any potential problems early. They may include:

• Blood tests at different stages of pregnancy, for example to check your blood group, iron levels, immunity to rubella, and for diabetes that can develop in pregnancy, as well as screening for some infections.
• A first-trimester ultrasound. This is a painless, non-invasive scan done in the first 3 months of pregnancy. It can confirm the number of babies and help estimate your due date.
• A second-trimester ultrasound, usually performed between about 18 and 20 weeks. It checks the baby’s development and monitors the size and position of the placenta. The baby’s sex can often be seen at this scan if you wish to know, although this is not always 100 per cent accurate.
• A third-trimester ultrasound, which may be offered in the last 3 months to check the baby’s growth, the fluid levels around the baby, and the position of the placenta.

Screening tests and diagnostic tests#

Tests for specific conditions, such as chromosome differences or genetic conditions that run in a family, are optional. You may or may not wish to have them, and you can discuss your options with your doctor, midwife or a genetic counselor before deciding.

It is important to understand the difference between screening tests and diagnostic tests. Screening tests can show how likely it is that a baby has a particular condition, but they cannot give a definite answer. For example, a result may suggest an increased chance or a low chance, or give an estimate such as one in 1,000.

A diagnostic test gives a more definite result. If a screening test suggests an increased chance, further tests are available to confirm the result.

Routine screening tests#

Examples of routine screening tests include:

• Combined first-trimester screening, which brings together information from a first-trimester ultrasound (including a measurement taken from the back of the baby’s neck, known as the nuchal translucency) and a blood test from the mother to estimate the chance of a group of chromosome differences, including Down syndrome.
• Second-trimester maternal serum screening, a blood test that helps estimate the chance of some conditions affecting the unborn baby, such as chromosome differences (including Down syndrome) or neural tube defects (such as spina bifida).
• Non-invasive prenatal testing (NIPT), also known as cell-free DNA screening. This blood test looks at the baby’s genetic material (DNA) found in the mother’s bloodstream. It can give information about the chance of conditions such as Down syndrome and some other chromosome differences, and can be done any time from about 10 weeks. It is more accurate than combined first-trimester screening or second-trimester maternal serum screening, but it usually costs more.

Some pregnancies are known to have an increased chance of a particular condition. For example, there may be a family history of an inherited disorder, or the mother may be older (the chance of a baby having a chromosome difference such as Down syndrome increases with age). In other cases, a screening test may have suggested an increased chance.

Diagnostic tests#

A diagnostic test can provide more definite information about whether a condition is present. Some diagnostic tests use a needle to collect a sample of placenta or amniotic fluid and carry a small risk of complications, including miscarriage. Diagnostic tests include:

• A detailed ultrasound, which may be used to check the baby’s health if there are unusual pregnancy symptoms, such as vaginal bleeding or reduced fetal movement.
• Chorionic villus sampling (CVS), which checks for specific conditions by taking a small sample of the placenta. Because the placenta originally formed from the same cells as the baby, testing it can give information about the baby. The doctor inserts a slender needle through the mother’s abdomen, guided by ultrasound, and the tissue (the chorionic villus sample) is examined in a laboratory.
• Amniocentesis, in which the doctor inserts a slender needle through the abdomen to withdraw a small amount of amniotic fluid, the fluid that surrounds the baby in the womb. This fluid contains some of the baby’s cells, which are then examined in the laboratory.

Because screening tests cannot give definitive information, many women who have an increased-chance result will go on to have a healthy pregnancy. The decision to have further tests to confirm whether a condition is present is up to the woman and her family, after discussion with her doctor or midwife.

Making decisions about testing#

Diagnostic tests may be considered for a range of reasons. If a test confirms a medical condition, some abnormalities can be treated, sometimes even before birth, and a woman and her baby may need specialist care before, during and after the birth. Knowing in advance that a baby has a particular condition can give a family time to prepare. Depending on the condition identified, some women or families may decide not to continue a pregnancy and to arrange a termination.

It is essential that health practitioners give families accurate, balanced information before and after screening and diagnostic testing, along with the time to make an informed decision. Good practice includes:

• Delivering high-chance or confirmed results using neutral, factual language (for example, “chance” rather than “risk”) and avoiding emotive terms such as “I’m sorry” or “bad news”.
• Providing up-to-date, evidence-based information on Down syndrome and other conditions being screened for, both before screening and after results are given.
• Offering referrals to peer support services, such as Down syndrome support associations.
• Offering non-directive counseling and support both before and after a decision is made about whether to continue a pregnancy.
• Respecting the decisions families make, not revisiting a decision once it has been communicated, while making clear that they have the right to change their mind.

Genetic counseling services are available through many large maternity hospitals.

Immunizations in pregnancy#

Immunization can help protect you and your unborn baby against some infectious diseases.

• The seasonal influenza vaccine (often called the flu shot) is recommended at any stage of pregnancy. It is considered safe in pregnancy and can provide protection for you and for your baby in the early months of life.
• A whooping cough (pertussis) vaccine, given as a combination vaccine that also protects against diphtheria and tetanus, is recommended during pregnancy. It helps protect your baby against whooping cough in the period before they can be fully vaccinated themselves.
• A COVID-19 vaccine may also be recommended.

Vaccine schedules and eligibility vary from place to place, so ask your doctor or immunization provider what is recommended for you.

Key points#

• A range of tests can confirm pregnancy and monitor the health of the mother and baby.
• Tests to confirm pregnancy detect the hormone βhCG and include home kits, urine tests and blood tests.
• Screening tests estimate the chance of a condition; diagnostic tests give a more definite answer.
• Diagnostic tests such as CVS and amniocentesis carry a small risk of complications, including miscarriage.
• All tests for specific conditions are optional, and you can discuss your choices with your doctor, midwife or a genetic counselor.

Where to get help#