Expert: Catherine Beier MS CBE - 3/13/2008

Question
I am currently single, my boyfriend and I have broken up recently due to relationship problems, however I am currently pregnant. my problem is paternity. my ex and I had been broken up for a few months and an old friend of mine came to visit, we had a few drinks and we had unprotected intercourse. later he mentioned to me that he had ejaculated in me. here are my facts in a timeline so i do not confuse you!

my LMP was October 28th, give or take a day, i had it on halloween for sure and the first few days of november. My period was also 7 or 8 days late in october. so my cycle length was about 36 or 37 days long.

I had sex with my old friend on november 6th.

I ran into my ex and we ended up meeting up 2 weeks after that and chatting. We had been together for close to three years and we decided to try it again. Anyhow, we had sex from the 15th or so and on, we stayed together up until recently, other issues we're having. I know we will stay together, just a little riff, probably stress related.

I had an ultrasound on january 2nd which stated i was 8 weeks and 1 day pregnant. The due date given was august 15th. I am wondering when i would have conceived, I have it worked out to the end of november, around the 20th. based on my period this seems off however i am not sure!

this is eating me up inside, is there a chance it is the old friends or does it have to be my boyfriends based on the dates?? I am concerned about how accurate and early ultrasound is and if the 8 weeks fetus could have been mistaken for a 9 or 10 weeks fetus....please help with any information you may have!

Answer
Jenna,

Early ultrasound is the most accurate way to determine a due date, especially if you have long and/or irregular cycles.

All babies develop at very similar rates in the beginning of pregnancy.  This is true up until after the first trimester when genetics and nutrition will have a bigger impact on the rest of their development.

Early ultrasound between 8-10 weeks gestation usually has a standard error of measure of +/- 1 day.  Depending on the equipment used, it can be up to 3 days, but not more than this.  This means that at the time of your ultrasound, you could have been 7wks,4 days to 8wks, 4days, but definitely not 9-10 weeks pregnant.

So, consider that due date to be quite accurate.  Since that's the case, it would mean you conceived with your boyfriend around 11-22-07.


Best,
Catherine