Hello,
Welcome to the ehealthforum and I am really glad to help you out.
Other than calcualting the gestational age by date of last menstrual period, Ultrasound scans alsooffer an alternative method of estimating gestational age. But the most accurate measurement for dating is the crown-rump length of the fetus, which can be done between 7 and 13 weeks of gestation. So ultrasounds at 7 weeks gestation are quite accurate.
Since you had intercourse with both partners close to ovulation, it is difficult to predict who is the father of the child. However, to confirm the same, Iâll suggest getting a paternity test.
I sincerely hope that helps. Take care.