QuestionI was just wondering, how accurate are early transvaginal ultrasounds? Does it matter if you do not know your LMP and can tell give you a pretty good estimate of when you may have gotten pregnant? Thank you.
AnswerCarmen,
Early transvaginal ultrasounds between 8-10 weeks are the most accurate, within +/- 3 days. In most cases, they are accurate within +/- 1 day. It does not matter if you do not know your LMP, although it can be helpful to determine if the growth rate is appropriate.
For example, if by your LMP you should be 10 weeks, but the ultrasound shows 5 weeks, then there may be a problem with the pregnancy. If you are supposed to be 10 weeks by LMP but are 13 weeks via ultrasound, then again, there could be a problem or you could have had implantation bleeding, not a true period.
In any case, a fairly reliable estimate of conception will also be determined, which is usually about 2 weeks less than the weeks you are pregnant (If you are told you're 10 weeks, 1 day, then you most likely conceived 8 weeks, 1 day ago).
Best,
Catherine
