My cousin is 7 months pregnant now, and on March 25, her ultrasound gave her a gestational age of 13 weeks and 1 day. Her given due date was Sept. 29.
We're trying to figure out the odds that the guy she slept with no later than the 21st of Dec. is the father. She may have stopped sooner than that, but definitely no later than the 21st.
Now, of course if she was dated 13 weeks and 1 day on March 25, that gives her a conception date of around January 6. Sperm from the 21st would be pretty impossible. But as we know, ultrasounds at 13 weeks can be off 7 or 8 days, right? And sperm can survive for 7 days at most inside the woman.
I'm just asking what you think the likelihood is that her ultrasound could have been off 9 days or more? That's the worst case scenario: assuming his sperm could last a full week and her ultrasound could be off 9+ days. That would be just enough for the pregnancy to happen. Sadly, I do not know if her measurements were CRL or BPD.
The guy from Dec. 21 was abusive, so we're hoping it isn't him. The guy after that would be a much better father and partner for her, if they chose to stay together. (If it's important, they were sleeping together from around Christmas to the middle of January. He's the most likely one by far, but let's focus on the first guy's likelihood.)
Obviously a paternity test would be the only way to know for sure, but we've been anxious as heck for 7 months.