How accurate are transvaginal ultrasounds in dating conception date if have irregular periods?

Pretty good: Transvaginal ultrasounds, especially early in pregnancy and repeated can be pretty accurate in determining the length getation and thus can calculate the date of conception.

Very good: Ultrasound uses measurements not dates to estimate the date of conception.

Very accurate.: The dating accuracy is within +/-3-5 days before 6 weeks, +/-5-7 days before 13 weeks. Take Folic Acid 1-5 mg daily!

Most Accurate: Transvaginal ultrasound is the most reliable way to determine a pregnancy due date. When done early, it can date a pregnancy within a few days and is more accurate than determining a due date of the last menstrual period.