To confirm the pregnancy (location of pregnancy, number of fetuses, viability/heart beat). The gestational sac is visualised as early as four and a half weeks of gestation. The embryo can be observed and measured by about five and a half weeks.

Ultrasound at this stage can also confirm the location of pregnancy within the cavity of the uterus (normal) or out of uterine cavity (ectopic pregnancy).

• To accurately date the pregnancy. This is particularly important for women who do not know the date of their last menstrual period, have an irregular cycle or have conceived whilst breastfeeding or soon after stopping the pill.
• To diagnose multiple pregnancy. Approximately 2% of natural conceptions and 10% of assisted conceptions result in a multiple pregnancies.
• To diagnose early pregnancy failure. Sadly, approximately 3% of women who attend for an early pregnancy scan will find that the fetus has died or has not developed. In this case we can arrange or advised as to other procedures that may be necessary.

The first trimester scan you should be offered is a Nuchal Translucency scan (NT Scan) between 11 and 13 weeks 6 days however the crown rum length (CRL) from the top of the baby’s head to the bottom of the spine should be within 45 and 84 mm.

The main reason for the NT scan is to assess of likelihood of a chromosomal abnormality, such as Down syndrome, however the NT scan can also reveal other conditions. If this is your first scan, then dating the pregnancy and diagnosing multiple pregnancies are another purpose of First trimester scan.

This scan can detect the gender of your baby. This scan is usually performed after 16 weeks of pregnancy.

• Confirm the gestation
• Confirm Gender

Determination is about 97% accurate by ultrasound.

It should be noted ultrasound cannot provide 100% confirmation, since in some occasions the images can be ambiguous or it is not possible to get good views.

Usually, a scan in the third trimester is done to check how well the baby is growing. Sometimes, the doctor or midwife may suggest a scan if they think baby’s measurements are smaller or larger than expected for the stage of pregnancy.

Other reasons for growth/ wellbeing scan are:

• Monitoring fetal growth
• Presentation of the baby (which way the baby is facing)
• Monitoring blood flow to the baby and placenta (called Dopplers)
• Position of placenta
• Amount of fluid around the baby
• Individual growth of babies in twins or triplets

A short cervix diagnosed by vaginal ultrasound has a good predictive value for preterm delivery, even in a low-risk pregnancy using vaginal ultrasound.

Women with risk factors for early preterm delivery because of previous surgery to cervix or previous early delivery will have this scan regularly in the first half of pregnancy.