Thanks for posting your query at DoctorSpring.com
Well, January 17 would be day 13 of your cycle, and January 12 would be 8 of your cycle.
It is very likely that you conceived on the 17th of January.
That is when ovulation is most likely.
Well plan B does inhibit ovulation, but then it has a 5 % failure rate, so you might be amongst that 5 %.
Only that can explain it.
You need to have an ultrasound dating scan, that will further confirm the dates.
Of course DNA paternity test is the only 100 % sure test.
All the best
Please feel free to discuss further.
Patient replied :
Thank you. That's what I was hoping to hear. Will the dating scan be completely accurate? Do I need to ask for that or will they automatically do that at my first visit?
Most centres do it around 12 weeks, and some centres do it at the first visit itself.
You would have to specifically ask at your centre, the earlier the better, for dating.
The dating scan also has an inherent error margin of 1 week, only a paternity test is 100 % sure.