Ultrasound timing

During pregnancy, most expectant mothers will have several ultrasound scans in order to check on the health and development of their baby. These are not compulsory and some mothers decide to forgo ultrasounds for personal reasons (such as avoiding anxiety), but they are recommended for every pregnant woman. Having scans at different times can offer a wider range of knowledge about the baby.

First trimester scans

Doctors now advise all pregnant women in their first trimester to have an ultrasound. Some women will have an initial scan early on, during their 6th or 7th week of pregnancy, particularly if they are experiencing bleeding or excessive pain. The first scan is a wonderful experience, though some mothers have their worries increased if they cannot see a heartbeat or the baby seems smaller than normal. If this happens you can talk to a midwife or sympathetic professional who will talk you through any problems.

The ultrasound which takes places between 10 and 14 weeks into pregnancy is known as a dating scan, and being aware of the dates can be vital for accuracy in later scans and tests, such as when the baby is examined for Down’s syndrome. This scan allows an accurate estimate of the baby’s age and the mother’s due date. Also noted in this scan is the baby’s development, including its limbs and heartbeat. Certain major problems can be detected at this stage, and it is helpful to find out about any problems early on. Multiple pregnancies such as twins or triplets are also identified, which allows the parents more time for preparation.

Second trimester: Anomaly scan

The anomaly scan is offered between 18 and 22 weeks into pregnancy. This is used to ensure that the baby is still developing normally, and to identify any potential problems that were not caught in an earlier scan. You can again see the developing baby’s heartbeat, face and hands, while the sonographer examines in detail for about 15 minutes. The sonographer will also be keen to check on the placenta’s current size and position. In the event of a low-lying placenta, a later scan will see whether the placenta has moved to a better position (the usual outcome); otherwise it can cause blockage of the womb and prompt a caesarean section for the birth. If you have had a scan before this point, the baby will now appear clearer and more fully formed. Most hospitals welcome the presence of a partner, children or other family members to share the experience with the mother. It is your decision whether or not a child is mature enough to handle the scan, particularly if any anomalies are discovered. The purpose of the scan is not to ascertain the baby’s sex, but many hospitals do provide this service. Remember that accuracy depends on multiple factors including the baby’s position during the scan, which is why some hospitals implement the policy of not disclosing whether they think the baby is a boy or girl.

Third trimester scans

Women who have given birth to a small baby in the past are advised to have a growth scan in the third trimester. This is also recommended for women having twins or with particular conditions like diabetes. If the baby seems much smaller than average (by feel of the mother or midwife, and the evidence of earlier ultrasounds), this can also prompt a growth scan. Occasionally a Doppler scan is used to check that the heartbeat and placenta are normal.