How to Determine the Father of a Baby by Conception Date. For some women, determining their baby's father can come with great difficulty. If you had multiple sexual partners and don't know the identity of your baby's father, use the following steps to help you determine your baby's father by first determining your conception date.
Determine the date on which you ovulated (released an egg). You can do this using several methods. You can determine your ovulation date using basal body temperature charting. You can also think back to the date of your last menstrual period and add two weeks to that date to get the ovulation date. Note that not all women ovulate two weeks after their menstrual period. This can serve as an approximation, however. You can also determine your ovulation date if your doctor gives you an ultrasound. Using an ultrasound to look at your baby, your doctor will be able to tell you how many weeks pregnant you are. If you subtract two weeks from this number and count backwards with a calendar, you can determine your approximate ovulation date.
Understand the relationship between conception and ovulation. Women typically can only get pregnant from sexual intercourse in the five days before ovulation and on the day of ovulation. This is because sperm can only survive for five days in fertile cervical fluid and because the egg can only survive for approximately one day. Therefore, if you know your date of ovulation, you will know the window in which you have conceived.
Remember your sexual partners from your conception window that you determined in Step 2.
Figure out your baby's father using the information from Steps 1 through 3. If you have only had one sexual partner during your conception window, that man is your baby's father. However, if you have had more than one sexual partner in your conception window, you can't determine your baby's father with 100 percent certainty. In this instance, you will want to take advantage of DNA testing after your baby is born to determine your baby's biological father.
If you are pregnant, be sure to visit your doctor for proper prenatal care. Talk to your own personal doctor if you need assistance in determining your conception date. You can also take advantage of websites that provide conception calculation assistance to determine the date you conceived. (See link in Resources.)