Calculating Conception Dates: Determining Paternity in Early Pregnancy

Calculation of Conception Date

I have been trying to conceive for over a year, and finally, I became pregnant.
However, I encountered a troubling situation that has left me feeling regretful and helpless.
I urgently need a doctor to help me determine my conception date, as I must confirm the identity of the father of my child.
My menstrual cycle lasts about 4 to 5 days, with a cycle length of approximately 30 days.
My last menstrual period started on February 19 and ended on February 22.
I had unprotected intercourse with a male friend on February 23 and February 27.
From February 28 to March 6, I had intercourse with my husband (as we are trying to conceive).
During this time, I used ovulation test strips from March 2 to March 5, with March 5 showing two very dark lines.
Prior to that, the tests showed one dark line and one very faint line.
My menstrual cycles have always been very regular, so when my period did not arrive on March 21, I took a pregnancy test, which surprisingly showed two dark red lines.
On March 26, I went to the obstetrics and gynecology department for a vaginal ultrasound, which revealed a small dot.
The doctor said that the gestational sac is forming and advised me to return in two weeks to check for a heartbeat.
I am both excited and scared.
Please help me understand if the dates of February 23 and 27 would be considered safe days, and whose child this might be.
Thank you very much.

JEAN, 30~39 year old female. Ask Date: 2018/04/16

Dr. Cao Guotao reply Obstetrics and Gynecology

Hello, February 23rd and 27th should theoretically be safe days.
Wishing you good health.

Reply Date: 2018/04/16

More Info

Determining the conception date and paternity in early pregnancy can be a complex issue, especially when there are multiple potential partners involved. Based on the information you've provided, let's break down the details to help clarify your situation.

First, it's important to understand how conception is typically calculated. The most common method is to start counting from the first day of your last menstrual period (LMP). In your case, your last menstrual period began on February 19 and lasted until February 22. Given your cycle length of approximately 30 days, ovulation likely occurred around 14 days after the first day of your last period, which would be around March 5. This is consistent with your observation of a strong positive result on the ovulation test on March 5, indicating that you were likely at your peak fertility during that time.

You mentioned having unprotected intercourse on February 23 and 27 with a male friend, and then from March 1 to March 5 with your husband. Since sperm can live inside the female reproductive tract for up to five days, it is possible that intercourse on February 23 could lead to conception if ovulation occurred shortly after. However, given that your ovulation test was strongest on March 5, it is more likely that conception occurred from intercourse on March 1 to March 5, especially since you were actively trying to conceive with your husband during this time.

The ultrasound on March 26 indicated that a gestational sac was forming, which aligns with the timeline of conception occurring around early March. If you were to calculate the estimated due date based on the first day of your last menstrual period, it would typically be around November 25, which is consistent with a conception date in early March.

Regarding your concern about the safety period, it is important to note that the concept of a "safe period" can be misleading. While there are days in the menstrual cycle when the likelihood of conception is lower, the variability in ovulation timing can make it difficult to predict. Given that you have a regular cycle, the days leading up to and including ovulation are considered high-risk for conception.

In terms of determining paternity, the timing of intercourse is crucial. Since the most likely conception window appears to be from March 1 to March 5, it would suggest that your husband is the likely father, especially since you were actively trying to conceive during that time. However, if there is still uncertainty, a paternity test can be performed after the baby is born, which would provide a definitive answer.

In conclusion, while it is understandable to have concerns about paternity, the timing of your ovulation and intercourse suggests that your husband is likely the father of the child. If you have further questions or concerns, it may be beneficial to discuss them with a healthcare provider who can offer personalized advice and support. Remember to take care of your health during this early stage of pregnancy, and best wishes for a healthy pregnancy journey ahead.

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