Dating Ultrasound (First Trimester)
The dating ultrasound — usually done at 8–12 weeks — confirms pregnancy viability, measures the embryo to establish gestational age, and calculates your due date. It's often the first time you see and hear your baby's heartbeat.
Typically performed: Weeks 8–12
What's Checked
The sonographer will:
- Confirm the pregnancy is in the uterus (not ectopic)
- Detect a heartbeat
- Measure crown-rump length (CRL) to establish gestational age
- Calculate your due date (EDD) based on CRL
- Check for twins or multiples
- Assess the uterus and ovaries
Transvaginal vs. Abdominal Ultrasound
Very early ultrasounds (before 8 weeks) are often done transvaginally for clearer images, as the embryo is too small to see clearly through the abdomen. After 10 weeks, abdominal ultrasound is usually sufficient.
Your Due Date
If the CRL-based due date differs from your LMP (last menstrual period) due date by more than 5–7 days, your due date will be changed to reflect the ultrasound measurement. The dating scan is considered more accurate than LMP calculation, particularly if your cycles are irregular.
Frequently Asked Questions
If no heartbeat is detected at 8 weeks or later, a follow-up scan is typically scheduled in 1–2 weeks before any conclusions are made. If seen at less than 7 weeks, the embryo may just be too small.
Usually no — at 8–12 weeks, it's too early to reliably determine sex from anatomy. Some technicians make early guesses, but these aren't reliable until 18–20 weeks.