Hallow Dear, The successive two intercourses with two different partners are barely a week apart. By date calculations, it is very difficult to derive about the probable intercourse responsible for the conception as the prediction of pregnancy dating varies by few days to a week by ultrasonography in early pregnancy. The due date also is derived by ultrasonography which may have such variation. If your due date is considered as April 27 2017, your last menstrual period date would be 20 July 2016 and intercourse in the first week of August would be responsible for the conception; however, this calculation is again not the perfect one. On September 6th, 2016, your ultrasound has calculated the pregnancy to be about 6-7 weeks duration. This infers that the conception would be due to intercourse around middle to third week of July; however, this is not a perfect calculation due to the variation of ultrasound calculations. However, if your menses are regular, you may tentatively guess about the probable intercourse responsible for pregnancy. The egg is released 14 days prior to the next expected period. Calculate which intercourse was on or nearer to this day. However, this also is not a fool proof method. The fool proof answer to your dilemma would be DNA test which will give you the scientific answer. I hope this helps you. Dr. Nishikant Shrotri