Expert: Dorothy H, LCCE - 4/18/2009

Question
QUESTION: I had sex with my ex on March 12(one day after my cycle ended). On march 21 I had sex with him again,and then on March 25 I had sex with a male friend(unprotected). On the 2nd of April I took a hpt and it was +. I went to the gyn on the 10th of april and had an u/s and was told I was 4weeks and 5 days. I also had a blood test on that same day(4/10) which put me at the end of 4weeks starting 5 weeks.Out of the 3 dates I had sex which one seems the most logic for my conception date?

ANSWER: Based on the infomation that you gave me, the most likely date of conception from the three dates you gave would have been March 21.

Dorothy Haines, LCCE

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

QUESTION: Thank you Dorothy for replying. I have a follow up question:
I went to the gyn again on Friday the 17th and this time he said that my gestional was 5 weeks and 5 days and the fetal age is about 3 weeks and 2 days. Do you still think that adds up to March 21 being my conception date?

Answer
If you are 5 weeks 6 days now, that would put the first date of your last period as March 7, and if your cycles are usually around 28 days, that puts the most likely date of conception around the 21-22nd, which would make the 21st the most likely date (sperm can live 3-5 days in the reproductive track, whereas the egg can only live 24 hours.)

However, if you tend to have long cycles (over 30 days)or irregular cycles and if your period started after March 7, then it is possible that you conceived March 25.  

Sincerely,

Dorothy Haines, LCCE