Antenatal dating scan explained

The scan can help establish an estimated due date, show whether more than one embryo or fetus is present, and assess features visible at that stage. It is a snapshot in time rather than a guarantee about the rest of the pregnancy.

A sonographer places an ultrasound probe on the abdomen with gel. If the pregnancy is too early to see clearly through the abdomen, a transvaginal scan may be offered; the probe is covered and inserted gently into the vagina with consent.

Measurements are compared with expected early growth to estimate gestational age. The calculated date may differ from one based on the last menstrual period because ovulation timing and cycle length vary. If findings are uncertain, the clinician may recommend another scan after an interval rather than drawing a conclusion from a single image.

Follow the clinic's instructions about bladder filling, since preparation differs by scan approach and pregnancy stage. Bring the date of the last menstrual period if known, information about fertility treatment, previous scan reports, and a list of medicines.

During the visit, you can ask the sonographer to explain which method is recommended and whether a support person may attend. Afterward, check who will discuss the report, whether the estimated due date changes the maternity schedule, and whether another assessment has been advised.

Do not wait for a scheduled dating scan if you develop vaginal bleeding, worsening pelvic or abdominal pain, shoulder-tip pain, dizziness, fainting, fever, or feel acutely unwell. These symptoms need prompt clinical assessment. Heavy bleeding, collapse, or severe pain with weakness requires emergency care.

Ask whether the pregnancy location and development were clearly seen, which due date will be used, and whether any view was limited. If follow-up is suggested, clarify its purpose, timing, and which new symptoms should lead to earlier review.