What should you know about dating scan weeks?

Pregnancy weeks are generally counted from the first day of the last menstrual period, even though conception happens later. An ultrasound estimate is based on measurements of the developing pregnancy and may adjust the expected due date. This is particularly helpful if periods are irregular, the last period is uncertain or conception followed fertility treatment.

The scan can look at the pregnancy location, development and whether a heartbeat is visible at the time of examination. A result that is unclear may lead to a repeat scan or blood tests, depending on the clinical picture. A nuchal translucency scan is a separate later examination.

Write down your period history, any fertility treatment dates and medicines you take. Follow the service's instructions about bladder preparation, and wear clothing that allows access to your abdomen. You can ask whether a support person may attend and how results are communicated.

Before leaving, check whether the estimated due date has been recorded and whether another scan or appointment is planned. If the scan measures a different stage than expected, ask what that means for follow-up rather than trying to interpret the number alone.

Seek prompt medical advice for heavy bleeding, severe or one-sided pain, fainting, marked dizziness, shoulder-tip pain or a sudden deterioration in how you feel. These warning symptoms should be assessed even if your planned scan is soon. Use the urgent service recommended by your maternity provider.

Ask which weeks are preferred for your scan, how the due date will be estimated, whether a repeat scan could be needed, what preparation is required and when the findings will be discussed. Ask which symptoms should lead you to seek help sooner.