Why are ultrasound scans used in pregnancy?

Posted on September 5, 2011

Ultrasound is considered to be the best way of investigating the foetus. It is considered to be very safe and non-invasive to mother and baby, accurate (from the help of modern technology) and cost effective. These scans are very important for all pregnant women, at all stages of their pregnancy.

There are many uses for ultrasound scans in the area of pregnancy. Firstly, the most obvious reason may be considered to be the diagnosis and confirmation of the pregnancy itself. The gestational sac can be seen as early as 4 weeks into pregnancy, and the yolk sac as early as 5 weeks – important parts of the embryo, and the development of the baby. The embryo can be observed and monitored from at least five and a half weeks, which can be of great use to women who have not been successful in pregnancy before; for example, have experienced miscarriages or have has trouble conceiving. Ultrasound scans can also confirm the site of the pregnancy, and discover ectopic pregnancies from an early stage.

Another important reason for ultrasound scans during pregnancy is determining the viability of the embryo, and to investigate vaginal bleeding in early pregnancy. Heartbeats can be visualised by around 6 weeks of pregnancy, and usually clearly depictable by 7 weeks. Around 5-8 weeks is where the embryo is at most risk from miscarriage and if the embryo’s heartbeat is below that of 90bpm, it is associated with a very high risk of miscarriage. Ultrasound scans are accurate at detecting these heartbeats and help the parents and doctors to determine the best course of action for the pregnancy.

Ultrasound scans also are a good instrument to determine gestational age and the assessment of the size of the foetus, especially in early gestation (around 5-11 weeks). Four measurements are usually made whilst performing the scan; firstly, the crown-rump length (CRL, measured at 7-13 weeks) and gives very accurate information of the age of the embryo/foetus. Secondly, the Biparietal Diameter is taken after 13 weeks, which measures the diameter between the two sides of the head. Thirdly, the femur length can be measured; the longest bone in the body reflects the longitudinal growth of the foetus. Fourthly, the abdominal circumference can be measured, the most important measurement in late pregnancy.

Lastly, malformations of the foetus can be diagnosed and monitored by ultrasound scans. These are usually made before 20 weeks and with most recent ultrasound equipment, cleft lips and cardiac abnormalities can be detected. In the first trimester of pregnancy, “ultrasonic soft markers” are used to detect abnormalities such as the lack of a foetal nasal bone, to enable detection of Down syndrome foetuses.

Ultrasound scans are of great usefulness in other areas as well. Intrauterine death can be detected and confirmed through this procedure; foetal movements, tone and breathing can be monitored in a Biophysical Profile, and scans can also diagnose uterine and pelvic abnormalities during pregnancy, for example an ovarian cyst. All of this is valuable to pregnant women and help monitor and keep the baby healthy through the full 9 months of pregnancy.

This entry was posted in News, Obstetric

Tom Farrell

Written by Tom Farrell

Tom Farrell works in both the NHS and private sector providing gynaecology, pregnancy ultrasound and maternity care clinics in the Jessop Wing (NHS) and BMI Thornbury & Claremont Hospital (Private sector) in Sheffield.

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The anxieties we had with our IVF pregnancy were allayed with the extra scans at Thornbury hospital with Tom Farrell. Helen (Sheffield)