What to know about a 12-week dating scan

It uses ultrasound rather than radiation. Measurements taken during the appointment can refine the estimated due date. Depending on local practice and your choices, the visit may also include nuchal translucency screening.

The sonographer looks for the pregnancy in the uterus, checks for a heartbeat where this should be visible, and measures the baby. Those measurements may date the pregnancy more accurately than the last menstrual period, especially when cycles are irregular or the period date is uncertain.

A reassuring result confirms what can be seen at that point; it cannot exclude every condition or predict the rest of the pregnancy. If an image or measurement is unclear, the maternity team may recommend another scan or a specialist discussion.

Follow the clinic's instructions about drinking water, because a comfortably full bladder may improve the abdominal view. Bring relevant pregnancy records and note the first day of your last period if known. Tell the sonographer about bleeding, pain, fertility treatment, previous ectopic pregnancy or uncertainty about dates.

Ask before the appointment whether screening is offered at the same visit and what choices you have. You can also ask when and how results will be explained.

Do not wait for a routine scan if you develop heavy vaginal bleeding, severe or worsening abdominal pain, pain focused on one side, shoulder-tip pain, fainting, marked dizziness or sudden weakness. Seek urgent medical assessment, as these symptoms can accompany internal bleeding or another pregnancy complication.

Contact your maternity service promptly for lighter bleeding, persistent cramps, fever, fluid loss or symptoms that concern you. The appropriate assessment depends on the symptoms, not on how close the scheduled scan is.

Useful questions include whether the pregnancy measurements match the expected dates, whether the estimated due date has changed, whether all planned views were obtained, and whether follow-up is needed. If screening is discussed, ask what the test can and cannot tell you and when its result will be available.