Antenatal Screening

All women will be offered a dating scan, and an 18- 20 week mid-pregnancy or fetal anomaly ultrasound scan. 

The main purpose of a dating scan is to check the stage of pregnancy and therefore when the baby is due. Measuring the baby can be more accurate than dating by the last menstrual period.

It is also an opportunity to check the baby is alive and developing as expected, and check for twins. This scan may also be part of your screening test for Down's syndrome (nuchal translucency scan).

Occasionally, if the baby is in an awkward position, an internal scan may be carried out, using a vaginal probe. We spoke to a few women who had experienced this.  They were not distressed by it, though for some people it may be embarrassing.

As with other scans, most women (and their partners) found it enjoyable and reassuring. They were relieved to see there really was a baby. The chance to take home a photograph was valued - a charge may be made for this.

Many people felt positive about the way staff talked them through what they were doing, including a woman who had seen scans before as a health professional. One woman described how special it seemed to her, whilst for the staff it seemed very routine. They did not say much and it seemed very quick.

Sometimes the 12-week scan is performed at the same time as the booking-in visit with the midwife, so there has been little time to discuss beforehand what might happen. For some people, the dating scan is the point when they discover that their baby has not survived. Several people described what a terrible shock this was, and how they did not feel prepared for this possibility.

Because they were not expecting any problems neither of these women had their partner with them, although both had taken a friend or relative instead and were glad not to be alone. One of them explained how she knew straight away from the behaviour of the person doing the scan (the sonographer) that something was wrong, even though she was supportive and tried not to make her anxious. She was given a photo to keep. Another mother who had paid for a private scan was touched that the staff returned her money when the baby was found to have died.

A dating scan cannot usually provide an assessment of the risk of the baby having Down's syndrome, but occasionally it can detect very obvious problems. This is something people did not feel well prepared for. This woman's dating scan was repeated twice that day, and she was eventually told that her baby's nuchal translucency looked very high. This meant the baby had more fluid than expected at the back of the neck.

It later turned out her baby had a serious chromosomal condition (Edwards' syndrome), and the couple decided to end the pregnancy. A mother who did not discover until 20 weeks that her baby's brain was not formed (anencephaly) had since heard that the condition can sometimes be picked up at the dating scan, although it was not in her case. She would have preferred earlier diagnosis.

For people who have discovered at a 12-week scan that something was wrong, scans in future pregnancies are nerve-racking, but they are also relieved and reassured if they can see the baby is alive and well.

A mother who had four miscarriages before her son was born with heart problems commented on how difficult it must be for staff to give bad news, but also described a really positive experience in an early heart scan at 14 weeks in her current pregnancy.

Occasionally, however, communication seems to lack empathy, as described by a woman who had ended her first pregnancy because her baby had anencephaly [undeveloped brain] and who had a bad experience with the 12-week scan in her next pregnancy.

Many experiences discussed here are common to other types of scan - see also Nuchal scans and '18-20 week scans'.

Last reviewed July 2017.
Last updated July 2017.