It is very important to know the date when your former girlfriend's last menstruation began and usual duration of her cycle. An ultrasound apparatus does not calculate the age of a pregnancy according to the calendar but measures the fetal dimensions and compare them with standard values. The results from such a calculation can be different than an age calculated with the calendar because fetal growth is not always standard during pregnancy. No doctor can guarantee an exact conception date. Conception usually occurs 2 weeks after the beginning of the last menstruation (around ovulation) if the cycle lasts 28 days (as in most women). If we accept the 22nd of May as a due date, then her last menstruation probably began on August 15th. This puts the conception date around August 29th. If the due date is the 20th of May, the conception day will be mathematically 2 days earlier. These mathematical calculations can’t be 100% sure. Only a paternity test can identify the real father. Your former girlfriend might be hiding something and this might be the real reason she's not interested in a paternity (DNA) test.


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