How to know when I got pregnant?

Can an exact date of conception be determined accurately without a paternity test? Many women have questions about the date of possible conception, and unfortunately figuring this out is not always so easy. The assumption is that if a woman has pretty regular menstrual cycles, then she will be ovulating during a certain time of the month. Ovulation is the time when conception can take place because that is when an egg is made available.

The problem is that most women do not ovulate on an exact date each month, and many women have a different ovulation day from month to month. If you also take into account that sperm can live in the body 3-5 days after intercourse has taken place, this can make figuring out conception very difficult.

Most doctors use the first day of the last period (LMP) and ultrasound measurements to gage the gestational age of a baby and determine when the baby was conceived. But these are just tools used to estimate the dates—it is very hard for anything to tell what the exact date of conception really is. Most people do not realize that ultrasounds can be off up to 5-7 days in early pregnancy and up to a couple weeks off if the first ultrasounds are done farther into the second trimester or beyond.

Due dates are not an accurate tool for determining conception since they also are only an estimation date (only 5% of women give birth on their due dates).

If you are seeking the estimated date of conception for paternity reasons, and intercourse with two different partners took place within 10 days of each other, we strongly encourage that paternity testing be done; this testing can be done during pregnancy or after the baby is born. This is the only way to accurately know who the father is.

http://www.americanpregnancy.org/prenataltesting/paternitytesting.html