A question stemming from the Vet Image Solutions Facebook page regarding gestational age motivated me to look at how reliable ultrasonography is for such an assessment. The majority of us take ultrasound imaging for granted when it comes to assessing the gestational age of a foetus during pregnancy, irrespective of our prior knowledge on either the maternal ovulation cycle or the date of proposed conception. However, is the calculation of gestational age really best carried out through the use of ultrasound imaging, and if so, why? The information contained in this article directly relates to human pregnancy, but the conclusions drawn can also be shared in incidences of veterinary pregnancy.

A suspected pregnancy will more than likely be confirmed with a pregnancy test followed by a visit to the doctor. It is then in the hands of the ultrasound practitioner to calculate the gestational age of the ever-growing foetus in order to give the expectant parents an idea of when delivery can be expected as well as to aid in the monitoring of foetal abnormalities throughout pregnancy. Currently, calculation of gestational age may be worked out either by identifying the date of the woman’s last known menstrual period, carrying out ultrasound imaging and/or following examination, although it is fair to say that ultrasonography is thought to be the most reliable method. Ultrasonography can also be used to identify other aspects of pregnancy that would be of interest to both the clinician and the parents, such as (although not limited to) the establishment of a placental-associated complication. Consequently, ultrasound imaging plays multiple useful, and some may even argue indispensable, roles throughout pregnancy.

Drawing on my own personal experience, here in the UK the NHS routinely offer 2 ultrasound scans during pregnancy – one at what is estimated to be 12 weeks of gestation, and the other at 20 weeks of gestation. There are obviously deviations from this schedule, particularly if the gestational age is not accurately known before the first scan is carried out, or if a pregnancy is considered 'higher risk'. Earlier on in pregnancy, age is calculated either by measuring the gestational sac or the crown-rump length, subsequently allowing a predicted delivery date to be worked out. It is usually preferable to predict gestational age earlier on, whereby clinicians exert more confidence in their findings due to the occurrence of less variation (particularly evident during the third trimester).

Despite there existing a variety of ways by which gestational age can be worked out, it is fair to conclude that ultrasonography is an essential technique here and a method that should always be employed where ever possible. Seeing as ultrasound imaging can be used with ease across the veterinary species, being able to calculate the gestational age and approximate delivery date of the animal in question will be of great use to breeders, farmers and veterinarians.