Obstetric (Pregnancy)

Ultrasound imaging in pregnancy is widely used to evaluate the baby. It can determine if a baby is present, the position of the fetus and if there is a multiple pregnancy. It can also help to diagnose abnormalities or problems, help determine the age of the pregnancy and subsequent due date as well as showing the position of the placenta in relation to the birth canal.

The Royal College of Obstetricians & Gynaecologists (in their 2000 document on Ultrasound Screening), recommend an Early Pregnancy Scan, undertaken before 15 weeks, which can combine the functions of the Early Viability Scan, Nuchal Translucency Scan and dating scan. There is also then a routine scan at 20 weeks. These two scans are the ‘minimum’ number of scans required during pregnancy and are offered by ¾ of ultrasound units in the UK. Individual circumstances may dictate that more scans may be offered and a breakdown of what you could receive is detailed below.

Early viability scan

This usually takes place at 6 to 10 weeks of pregnancy. The scan can confirm the number of babies in the uterus, the embryo can be observed and measured by about five and a half weeks and a heartbeat usually detected by 6 weeks. Scans at this stage in pregnancy are reassuring for women experiencing bleeding, pain or who have had previous miscarriages. Transvaginal scanning may also be used to obtain a better image of the womb.

Nuchal translucency scan

This is a scan which is usually carried out at 11-13 weeks and is a method of screening for chromosomal abnormalities without having an invasive test such as an amniocentesis. The nuchal translucency is a measurement of an area of fluid behind the baby’s neck. An increase in the amount of fluid may indicate an increased risk of a chromosomal abnormality, such as Down’s syndrome. This has an accuracy of about 70% and can lead to recommendations for further testing, such as an amniocentesis.

Pregnancy Dating

Gestational age is usually determined by the date of the woman's last menstrual period - assuming ovulation occurred on day fourteen of the menstrual cycle. Ultrasound scans offer an alternative method of estimating gestational age. The most accurate measurement for dating is the crown-rump length of the fetus, which can be done between 7 and 13 weeks of gestation. After 13 weeks gestation, the fetal age may be estimated by the diameter of the head and the length of the femur. Dating is more accurate when done early in the pregnancy. When a later scan gives a different estimate of gestational age, the estimated age is not normally changed but rather it is assumed the fetus is not growing at the expected rate.

 Anomaly scan and fetal sex determination (20 weeks scan)

This scan is a routine scan in the UK which takes place at around 20 weeks. This is one of the best times to have an ultrasound done as most infants are the same size at this stage of development. A thorough examination of the fetus’s brain, heart, spine, kidneys, organs and limbs will be carried out and the placenta checked for its position. Measurements of the fetus will also be taken to ensure it is growing normally. At this point, should you wish to know the sex of your baby, you can ask the sonographer to tell you. Although this is usually fairly accurate, it can not be taken as a guarantee of sex as ultrasound is not 100% accurate. This scan is the most significant one undertaken during pregnancy, because it can reassure the parents that everything appears to be as it should be. If a potential problem is indicated, a further follow up scan may be needed. If this does occur, the possible complications of or implications for the pregnancy will be fully discussed with the parents by a doctor or consultant and advice and guidance will be provided.

Souvenir Scanning

Developments in real-time 3D and 4D ultrasonic imaging have led to parents asking for souvenir (keepsake) video recordings of the fetus, sometimes at several stages during the pregnancy. Anyone who wishes to have a “keepsake” scan carried out at a private clinic should ensure that the person carrying out the scan is fully qualified. Since such scans are performed for non-diagnostic purposes, potential clients should ensure that the clinic has procedures in place to deal with any incidental findings, such as the finding of fetal abnormality, in a sensitive and professional manner, and that the ultrasound equipment is operated at settings which conform to the BMUS guidelines for non-diagnostic scanning. A balance must always be maintained between diagnostic benefit and risk to the patient.

The position of BMUS on the use of ultrasound to produce “keepsake” images of the fetus is outlined in the European Committee of Medical Ultrasound Safety (ECMUS) statement, endorsed by BMUS. The views expressed in this statement are that:

1. Ultrasound scans should not be performed solely for producing souvenir images or recordings of a fetus or embryo.

2. The production of souvenir images or recordings for the parents to keep is reasonable if they are produced during a diagnostic scan, provided that this does not require the ultrasound exposure to be greater in time or magnitude (as indicated by the displayed MI and TI) than that necessary to produce the required diagnostic information.

3. Attention is drawn to the recommendation of the EFSUMB Clinical Safety Statement for Diagnostic Ultrasound that ultrasound examinations should be performed only by competent personnel who are trained and updated in ultrasound safety matters.

For all Obstetrics scans, no special preparation is needed, although it is best to wear loose clothing that can easily be lifted or removed in order to expose your abdomen. You will lie on your back on an examination couch and the transducer moved back and forth across your stomach in order to gain the best possible image of the fetus. 

Download - Patient Information Leaflet

CARE Quality Commission (CQC) advice - Choosing a baby scanning service