Expert: Dorothy H, LCCE - 10/28/2009

Question
QUESTION: I have been tracking my periods this year because in pass years they have been really off due to bc. my periods are as follows 12/13/08, 1/28/09/ 3/6/09, 4/12/09, 5/17/09 and 6/29/09. My lp seems to be every 14 days. the problem is I don't know when my period was in aug. I found out i was pregnant on 9/19/09. I went to the doc for a transvaginal u/s on 10/7/09, they told me I was 9 weeks 3 days and gave me a due date of 5/9/09. Given all this long infomation lol, do you think i could have gotten pregnant anytime before the 13th of Aug?

ANSWER: Hi Tasha,

A transvaginal ultrasound done at 9 weeks is generally very accurate but it can be off by +/-3 days.  That ultrasound puts your LMP at August 2 (which seems to fit in with your cycles) and puts conception around August 16.  

Because the conception date could be up to 3 days off and also because sperm can live in the reproductive track for 3-5 days, it is possible but not likely that having sex before August 13 resulted in your pregnancy. However, I don't think it's likely at all that you conceived before August 9.

I think it's much more likely that you conceived after August 13 than before August 13.

I hope that helps!

Dorothy Haines, LCCE

---------- FOLLOW-UP ----------

QUESTION: thank you for answering my question. So based off of your knowledge, if I had sex on 8/6/09 and 8/14 and 8/17, I prob couldn't have conceived by having sex on 86/09, because the sperm would have or should have been dead by at least aug 11th right?

Answer
If you had sex on August 6, the sperm would have died probably by August 9 and definitely by August 11.  The transvaginal ultrasound at 9 weeks puts conception at somewhere between August 13-19. It is highly unlikely that a transvaginal ultrasound at 9 weeks would be off by more than 3 days.