2 possibles or

[MiellaGrace]

My LMP was 3/26 for sure. I had sex 4/1 but I’m sure it was protected and I don’t recall is breaking. On 4/7&4/11 I had sex with a new partner and he certainly finished inside both times. I thought my due date was 12/31 but u/a said 12/27… what do you think?

[ppowb]

In my book it is unusual to get pregnant on cycle day 6. CD8 is the conventional beginning of the fertile window. Your poorly protected sex with the new partner was spot on for a 28-31 cycle. Dec 31 is a good calculated date for a 3/26 LMP. If your due date is now showing earlier, it may just be a bigger than average baby.

[AnnieBrooke]

By "u/a," do you mean an ultrasound? (The only medical use of it I can find has to do with urinalysis.)

If your due date of 12/27 was given to you by an ultrasound, when was the ultrasound done?

Did you get the date of December 31 from a doctor or just counting forward from your last period? And if so, are your menstrual months regular at 28 days or do they vary?

[MiellaGrace]

Sorry spellcheck yes u/s . I’m high risk so I had an extremely early u/s to see if I would be on progesterone. I thought I was just about 5w or so but u/s showed I was about 4 days ahead . I guessed 12/31 as due date from my LMP.  My cycles are usually 28-31 days . My feb cycles was 31 days instead of my norm 28/29 days . So I initially expected my period 3/22

[AnnieBrooke]

When you say "I was about 4 days ahead," do you mean the pregnancy seems to have began further along on the calendar than you thought? (Or would you consider that "behind?") For ease of understanding, could you say the date of the ultrasound, and what its estimate of your GA was, on that day?

[AnnieBrooke]

I am trying to get the details this specifically because you're talking about timing with not much margin for error. With no date given for the ultrasound and saying you were 'about' 4 days ahead of 'about' 5 weeks, any opinion would be more guess than analysis.

[MiellaGrace]

On 5/5 was about 6w 2day but I thought I was around 5w or so. I can’t remember exactly but I’m measuring further along than I would have thought .

[AnnieBrooke]

From what you explained, you had sex with one guy on April 1 that you're "sure it was protected," and had sex April 7 and 11 with a different guy that wasn't protected. Then you had an ultrasound that gave you a due date of December 27.  (Did that December 27 due date come from the May 5 ultrasound or from a later ultrasound?)

You said you expected to be about 5w when you had your first ultrasound (presumably you're talking about the one May 5), but that the ultrasound "showed I was about 4 days ahead." Then just above, you said you were "about 6w 2day" when you had the ultrasound. (Was that a different ultrasound, or just a typo for 5w2d?) Usually an ultrasound lists your days and weeks GA right on the face of the ultrasound, but your conditional wording when giving the GA suggests you don't have that. Is there nothing written on the ultrasound? (Or, did they not give you a copy?)

Anyway, assuming you got the due date of December 27 from the first ultrasound (and assuming the due date hasn't been changed when you have had subsequent ultrasounds), sex from either April 1 or April 7 could have gotten you pregnant. The chances of the father being the guy with whom you didn't use protection are higher. But protection can fail, and if it did on April 1, the guy's sperm could have lived long enough in your system to be there and viable through at least April 5 or 6, and you could have ovulated then.

If you have the specific GA listed on the front of the May 5 ultrasound, by all means write back and say what it is. It might help pinpoint one guy or the other as the most possible.