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How Early Can I Find Out Who the Father Is?

“How early can I find out who the father is?” This might be considered by some to be an awkward question. If you have just found out you’re pregnant, however, and need to be asking this question, it’s a really important one for you. It’s also important for you to be able to ask it in a safe, nonjudgmental environment. Avenue Women’s Center can be that environment for you.

At Avenue Women’s Center, we understand that every woman’s situation is unique. We are a first step resource for Chicagoland women facing an unplanned pregnancy. We support women through their unique situations with confidentiality, care, and compassion. Please contact us and allow us to walk with you through the challenging journey you are facing.

Finding Out Who the Father Is

Whatever the circumstances that have brought you to this place, whatever your reasons why you need to ask it, the answer to your question about how to find out who the father is may well have great significance in determining what course you will pursue next.

Here are a few things you can do when you’re not sure who the father is.

Gather your information.

  • Identify and list dates of sexual activity
  • Confirm the date when your last menstrual period started
  • Clarify information about your cycles. How long do they typically last? How regular are you? Are you able to estimate when you ovulate in the course of your cycle?

Consult professionals.

Have you had an ultrasound to determine the likely due date? An ultrasound may be helpful in identifying the possible time of conception. However, there are variables that can impact the accuracy of this calculation as well. More information about that follows later in this article.

Using Ultrasound to Determine Conception

A number of factors can make it difficult to determine precisely the time of conception. These include whether or not a woman has a regular 28-day cycle and the fact that ovulation does not necessarily take place at the same time from month to month. After ovulation, the egg usually remains in the fallopian tube for up to about 24 hours. There, it may be fertilized by a sperm. Sperm may remain in the body up to 3-5 days after intercourse. These variables contribute to the difficulty in pinpointing the exact time of conception for the purpose of establishing paternity.

When trying to determine the time of conception with an ultrasound, the age of the pregnancy is estimated by fetal measurements that are taken by the physician or sonographer. Since a fetus may be larger or smaller than average, the measurements may not give a completely accurate conclusion. Additionally, based on when the ultrasound is done, date calculations can be off by as much as one to two weeks. The best accuracy in identifying the conception date is during the first trimester, from the 8th to the 14th week of gestation. The earlier the ultrasound, the more accurate will be the estimation. If the ultrasound is done later in the pregnancy, the calculation becomes less accurate.

In light of all these variables and qualifications, it’s probably safest to say that the best possible calculations based on likely time of conception, or even by ultrasound, are often not a reliable method for identifying paternity. According to the American Pregnancy Association, “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.”*

There are other reliable ways to identify paternity, including tests that are legally admissible if this is a concern for you. We’ll share more about these in a subsequent posting, so please come back to our blog for further information.

If you are asking the question, “How early can I find out who the father is?” Avenue is here to help. We offer you four decades of experience and compassionate care for the challenges ahead of you. Please call, text, email, or chat to set up a private appointment at one of our six DuPage County locations.  We will be honored to serve you.


  • * American Pregnancy Association. (2017, March). Paternity Testing. Retrieved from:
  • American College of Obstetricians and Gynecologists. (2017, May). Methods for Estimating the Due Date. Retrieved from:
  • American Pregnancy Association. ( 2017, March). Calculating Conception. Retrieved from:
  • Estimating Your Conception Date. Retrieved from:
  • Healthline. Tests During Pergnancy: the Abdominal Ultrasound. Retrieved from:
  • WebMD. (2016, August). Pregnancy and Conception. Retrieved from:

Reviewed by Patricia Kuenzi, APN-CNP, MSN, ANP, PNP.

The information provided here is general in nature.  It is not a substitute for a consultation with a medical professional. Before any medical procedure, it is imperative that you discuss your personal medical history, risks, and concerns with your doctor. If you have questions during or after a procedure, your doctor should be immediately contacted. Avenue Women’s Center is not an emergency center.  If you are experiencing severe symptoms, such as bleeding and/or pain, seek immediate medical attention.  Contact your physician, go to an emergency room, or call 911.