Pregnancy scans and screening tests

You can have a dating scan and say no to genetic screening. You can also choose all, some or none of the screening tests you’re offered. A scan appointment is a chance to talk about these choices. Going to the scan doesn’t mean you’ve agreed to anything else.

What a scan can look for

An ultrasound scan uses sound waves to make a picture of the baby in the womb. A sonographer usually puts gel on your tummy and moves a probe over it. They may need to press a little to get a clear view. If the baby’s position makes it hard to get clear pictures, the scan may take longer or need to be done again.

In England, the first routine scan is offered at 11 to 14 weeks. It helps work out your due date and can show whether there’s more than one baby. The mid-pregnancy scan is usually at 18 to 21 weeks and is also called the anomaly scan. It checks for some physical conditions. Neither scan can find every possible health condition.

Screening and diagnostic tests answer different questions

Screening estimates the chance of a particular condition. It can help you decide whether you want more information, but it can’t give you certainty. Diagnostic tests can confirm whether certain conditions are there. Examples include chorionic villus sampling (CVS) and amniocentesis.

CVS tests a small sample of cells from the placenta. Amniocentesis takes fluid and cells from the sac around the baby for testing. These are separate procedures from a screening blood test. Before you decide, ask what a test can find, what it can’t find and what its possible risks are.

The NHS combined test, quadruple test and NIPT

The combined test screens for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome. It combines a blood test at 10 to 14 weeks with a measurement of the fluid at the back of the baby’s neck, taken during the scan at 11 to 14 weeks. The blood test and scan may be done together or separately.

If the combined test wasn’t possible, the NHS offers a quadruple blood test, usually at 14 to 20 weeks. This screens for Down’s syndrome. It doesn’t replace the mid-pregnancy scan, which also looks for signs of Edwards’ and Patau’s syndromes.

After a higher-chance screening result, the NHS offers some choices. You can have non-invasive prenatal testing (NIPT), which is a more accurate screening blood test. You can have CVS or amniocentesis. Or you can choose no more tests. NIPT is still a screening test. The maternity team can explain each option without assuming what you’ll choose.

How the US and international offers differ

ACOG says both screening and diagnostic tests are offered to all pregnant women. Its guidance describes cell-free DNA screening from 10 weeks. This test looks at DNA from the placenta that has passed into your blood. It describes an anatomy scan between 18 weeks and 22 weeks. The US quad test also screens for Edwards syndrome and neural tube defects (problems with the brain and spine), so it isn’t the same as the NHS quad test.

WHO recommends an ultrasound scan before 24 weeks. This international advice doesn’t list every test available in each country. Ask your local maternity service which screening programme it uses and which decisions need to be made by a certain time.

Getting help with choices and results

Contact your midwife or GP in the UK, your obstetric clinician in the US, or your doctor or midwife elsewhere if you need help deciding, or haven’t had a result you were expecting. The NHS advises contacting your midwife or GP if you’re between 10 and 14 weeks and haven’t been offered screening for chromosome conditions. Before you leave an appointment, ask how you’ll get your results and who to contact if they don’t arrive.

ACOG describes different reasons people choose to have tests or say no, including getting ready to care for a baby. Ask to talk through what you’d want to know and how you might use that information.