Expert: Catherine Beier MS CBE - 1/12/2009

Question
In May, my boyfriend & I had a separation for about a month. I went back to my previous ex & was w/ him sexually only once. I do not know the exact date, but I know it was on or before May 21st, 08. Now I am 32 weeks pregnant w/ EDD
Mar. 11th, 09. My periods are very irregular, so it's difficult to determine my ovulation date. Here is the list of dates as I know them:

5/12/08 possible LMP -ususally last no more than 4 days, spotting, irregular
5/21/08 On or before this date was the last time I was w/ ex sexually
5/24/08 reconciled w/ current boyfriend & have been w/ him only ever since
6/05/08 negative home pregnancy test
6/17/08 my doctor later quoted my conception date
6/27/08 positive home pregnancy test
6/30/08 vaginal sonogram #1, nothing shows, no sac or baby
7/10/08 sonogram#2 shows sac only 5wks, 2days
7/24/08 sonogram #3 shows sac & small seed-like baby; 7wks 1 day

Questions:
What is the difference between conception date & the date of
intercourse?
At what # of weeks should the baby show in a sonogram & how accurate are they?
I keep getting different conception dates from various sources, all in June 2008, some agreeing w/ my doctor on 6/17/08, while others go to the first week of June. Is it a possibility my ex is the father considering when we had intercourse?

I would appreciate any advice.  

Answer
Anita,


Let's address your questions one at a time.

1.  The conception date is when you actually conceive.  It is typically not the same day you had intercourse because sperm can live for up to 5 days in the reproductive tract, meaning you could have conceived 5 days after having intercourse.


Conception typically occurs from having intercourse in the 2 days prior to ovulation.  It takes the sperm a while to swim through the reproductive tract to reach the egg and fertilize it, so the best chances of conceiving are when the sperm are already in the body.



2.  The baby typically doesn't show in the ultrasound until about 6 weeks.  Early transvaginal ultrasound between 8-10 weeks is the most accurate way to assess fetal age and is typically accurate within +/- 2 days at most.  Ultrasound becomes less reliable as your pregnancy progresses, eventually with a margin of error of +/- 2 weeks.


3.  There is no way your ex was the father.  You definitely conceived in June and based on your dates from ultrasounds, it was around the 17-18th of June.




Best,
Catherine