Pregnancy scans and screening tests

You can accept a dating scan and decline genetic screening. You can also choose all, some or none of the screening tests offered. A scan appointment is a chance to discuss those choices; agreeing to attend leaves those decisions open.

What a scan can look for

Ultrasound 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 apply some pressure to get a clear view. If the baby’s position makes it hard to get clear images, the scan may take longer or need repeating.

In England, the first routine scan is offered at 11 to 14 weeks. It helps estimate the due date and can show whether there is 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 certain physical conditions. Neither scan can identify 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 further information, but it cannot provide certainty. Diagnostic tests can confirm whether certain conditions are present. Examples include chorionic villus sampling, usually shortened to 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. Ask what a proposed test can find, what it cannot find and what its possible risks are before deciding.

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 fluid at the back of the baby’s neck during the scan at 11 to 14 weeks. The blood test and scan may be done together or separately.

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

After a higher-chance screening result, NHS choices include non-invasive prenatal testing, or NIPT, a more accurate screening blood test; CVS or amniocentesis; or no further tests. NIPT is still a screening test. The maternity team can explain each option without assuming which choice you want to make.

How the US and international offers differ

ACOG says both screening and diagnostic testing are offered to all pregnant women. Its guidance describes cell-free DNA screening, which examines DNA released from the placenta into your blood, starting at 10 weeks. It describes an anatomy ultrasound between 18 weeks and 22 weeks. The US quad test also screens for Edwards syndrome and neural tube defects, so it is not identical to the NHS quad-test offer.

WHO recommends an ultrasound scan before 24 weeks. This international recommendation does not list every test available in each country. Ask your local maternity service which screening programme it uses and which decisions have a time window.

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 have not received an expected result. The NHS advises contacting your midwife or GP if you are between 10 and 14 weeks and have not been offered the chromosome screening. Ask before leaving an appointment how results will arrive and who to contact if they do not.

ACOG describes different reasons people choose testing or decline it, including preparing for a baby’s care. Ask to talk through what you would want to know and how you might use that information.