Really worried...

[me28715]

I am really concerned because I had sex with a friend from work on Dec 17th.  I got back together with my husband very soon after.  The friend and I did not use a condom but he did not ejaculate inside of me. My husband and I didnt use a condom and he did ejaculate inside.  I had a period on Jan 5th.  The first of Feb, I discovered I was pregnant.  My doc determined my due date to be Oct 16th because of my last period, which puts me at 24 weeks, 2 days.  I had an ultrasound and it showed that I was 25 weeks, 3 days-which is 8 days further along than expected.  My doctor says he is leaving my due date at Oct 16th.  I am concerned that the friend is the father...is that possible? What day did I conceive?

[AnnieBrooke]

A doctor, nurse, ultrasonographer, or anyone else in the medical profession including researchers and medical textbook editors and writers, uses gestational age, not conception, as a start point on a pregnancy.  Gestational age (GA) begins on the first day of your last period.  The January 9 date was an estimated first day of your last period based on the size of your baby.  Doctors don't think a woman who is on the first day of her period is pregnant, but the first day of bleeding is a traditional beginning of the count (in the old days, there were no ultrasounds, and they had to tag the count to something).  They will tell you a possible date of conception pretty much only if you ask them, and you have to specifically say "conception."  It's normal for them to talk about pregnancy using GA.

That is why the conception calculator gives the following based on the due date of October 16:

     First day of last menstrual period:  January 9
     Probable date of ovulation:  January 23
     Possible dates of conception:  January 19 to 27
     Due date:  October 16 (40 weeks)

Since the estimated first day of your period (based on the measurements of the actual baby), is only 4 days off when your real period was, count the January 23 date as accurate to within four days, i.e., a range of January 19 - 23.  Your side guy, having had sex with you on January 21, is unfortunately right smack in the middle of that time, especially when you consider the length of time sperm can live.  On the other hand, so is your husband.  They could both have had viable sperm in your system on January 23.

Sorry this is not something you can use to definitely rule out the wrong guy, but you just can't.  Especially if the sex was unprotected, whether or not he ejaculated is unfortunately not enough to be sure.  (You've heard of pre-ejaculatory fluid having sperm in it in some situations, I am sure.)

A DNA test, as I said, is the only way to know for sure.

[me28715]

I guess I am confused because the vaginal ultrasound measured the baby at 5 weeks old on Feb 14th, putting the date at Jan 9th. Wouldn't that be the date of conception?

[AnnieBrooke]

*21st of January, not 19th

[AnnieBrooke]

Hate to say it, but you will definitely need a DNA test.  There is no way to write the guy off with whom you had sex on the 19th of January.  It doesn't matter that he didn't ejaculate, especially if the sex was unprotected.

I assume you have not confessed to your husband that even after you got back together, you had sex with someone else?  If you fully intend never to have such a lapse again, then you might just test with the boyfriend and not ever tell your husband anything if the DNA test shows the baby is not from the boyfriend.  But if you think the marriage is shaky anyway, I would consider testing with both men.  Obviously this means confessing, but really, if you think it might happen again (or if it is a signal of other issues that might mean the marriage is not going to last) what is the point of hiding the truth?  It's a material piece of information for your husband, that you cheated.  He deserves to know as much as you would deserve to know if the situations were reversed.  And it matters to the child -- you need to know who the dad is.

[me28715]

The 23rd is possible...I am just not sure.  We are pregnant with a boy.

[AnnieBrooke]

Are you sure you didn't have sex with your husband around the 23rd?  If you are positive, then the question is, when *did* you last have sex with him before the 19th?  Your husband's sperm could have lived in your system for several days, so even if you didn't have sex with him on the exact day of ovulation, you could still have gotten pregnant with his sperm that was waiting around.  If you're pregnant with a girl, that makes this possibility more likely.

[me28715]

I had a vaginal ultrasound on Feb 14th, and it said I was 5 wk, 1 day I believe.  I had another on Mar 11, and it said I was 9 weeks, 2 days which was about 4 days ahead of the previous one.

[me28715]

This is my other problem...during that time my relationship was on again off again with my husband...I had sex with that guy one other time on January 21st I believe, but he did not ejaculate...Your response about conception date has me really worried.

[me28715]

Yes...I have had several..the earliest ones said I was 8 days further along than the original day.  The last one I had, said I was 4 days further along...

[AnnieBrooke]

Do you have an earlier ultrasound than the one in your 25th week?

[me28715]

Thanks for the response...although my period started on January 5th and lasted only 3 days, which is abnormal for me, I still am worrying over nothing?  Because I don't remember the exact dates I had sex with my husband, but I know it was not during that Jan 19-27 range because I was working heavy hours that week.

[AnnieBrooke]

Hi, me28715, I assume you know that over time in a pregnancy, ultrasounds get less accurate for purposes of dating the pregnancy to the point where by the final weeks they can be off by two weeks or even more.  (Though babies all start out the same size, they grow at different rates.)  For that reason, if the ultrasound at 25w3d was your first one, it is no more than broadly useful as a dating tool.  (I.e., it can narrow down the month but certainly not the day.  The 8-day discrepancy you've named could just be the standard margin for error in action.)  Did you happen to have any other ultrasounds, perhaps earlier in your pregnancy?

That said, you are worrying about an event that was more than a month before you would have gotten pregnant.  It's not like it's even close.  Along with the wide gap in time, you also had a period more than two weeks after having had sex with Mr. Wrong.  Women who are pregnant don't commonly have periods, no matter how often someone posts on the Internet a story that someone they know once told them that they had an aunt who had periods all through her pregnancy.

Here is what the conception calculator gives based on the due date of October 16:

     First day of last menstrual period:  January 9
     Probable date of ovulation:  January 23
     Possible dates of conception:  January 19 to 27
     Due date:  October 16 (40 weeks)

Since the period is only 4 days off when your real period was, count the January 23 date as accurate to within four days, i.e., a range of January 19 - 23).  It has nothing to do with December, let alone December 17.

Don't worry about paternity.