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What is it that makes you pretty sure that you ovulated on 11/30
Since you had typical symptoms of ovulation on 12/1/15, which is consistent with the LMP, it is very possible that that the ultrasound is off by a several days. The accuracy of a first trimester ultrasound is +/- about 8%, which would include the time frame that includes ovulation on 12/1.
However, neither symptoms, Lcx, or a first trimester ultrasound are able to accurately differentiate between two potential fathers with whom you engaged in intercourse 6 days apart, so it is impossible to state with certainty who is the father based solely on this information. There is more support for the fatherhood of the partner of 11/30, but it cannot be stated with certainty.
If I can provide any additional information, please let me know.