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Who is the father?

My first day of my last period was January 15th. My cyle is about 28 days. I had sex on the 23rd of January with guy #1. I had sex with guy #2 January 27th. My period calendar says I ovulated the 28th. Could it be either guy?
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134578 tn?1546634665
Could what be either guy? Are you pregnant?
Yes 5 weeks which was caculatated from my first day of my last period
Did you do the calculation, or did the doctor do it when looking at the measurements of the baby on an ultrasound?
If it was you and not the doctor, do you have access to an ob/gyn who will do an ultrasound scan if you ask for one? If so, get one in your 6th or 7th week from the first day of your last period, meaning no earlier than next week but no later than the week after that. Ask the doctor to assess the due date of the baby just from the baby's measurements, not using the first day of your last period in the assessment.

The problem this advice is trying to address is, you can't count forward from a last period and get a reliable idea of when you next ovulated, no matter what your app says.

Ovulation is the starting event, and the period is the ending event. But then the next ovulation comes again whenever it feels like it, it's up to the brain, not the last period, to send the chemical signals to begin the ovulation process. So though there is a roughly certain time between ovulating and the period that does the clean-up work from it, it's anyone's guess how long it will be to the next ovulation. The period does not start anything, it finishes it.

This makes counting forward from the first day of your last period useless or even misleading, Most women are not really regular enough to assume they ovulate exactly at mid-cycle. I know apps use that assumption, but that is because apps have to use averages or they can't guess at anything at all.

You need precision in measuring, and you need to rule in or out the possibility of having ovulated at the time when you had live sperm in your body from each man. For this, you need an ultrasound. (You can also do a prenatal DNA test, but let's take the easy one first.)

Go to your doc and have an ultrasound done, and ask the doctor to give you an estimated due date based only on the embryo's crown-to-rump measurement and other developmental markers, not on when your last period was. (Say you don't remember when it was, or that your cycles are too irregular to count on, if you want to be sure the doctor is not influenced by when your last period came.)  Best time for the ultrasound would be in your sixth or seventh week.  5th week is too early (because sometimes a woman's fifth week from her last period is not really her third week since conception for the reason mentioned above -- women can ovulate whenever). And after the 7th week, babies' growth rates can begin to diverge from the average, to the point where by the woman's 40th week the margin for error is +/- 3 weeks.  

Once the doctor gives you an estimated due date (a calendar date, not "x weeks"), take it home and put it into an online conception calculator or just count back 266 days from it and that will be your estimated date of conception.

If you are super lucky, your estimated date of conception will suggest one guy and not the other. For it to do that, it would have to point pretty clearly to well before January 27 (like, January 23 or 24 or maybe 25), or to after January 29.  (This is due to the long life of sperm in your body.) A date in the middle gives you a predicament.

There are prenatal DNA tests. They cost a whole ton of money and only a few labs have a good reputation. Try the ultrasound route first, possibly it will give you the answer you need.

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