When Did I Conceive? Your Fertility Timeline

What is the date of conception?

Hello Doctor, my menstrual period started normally on February 10, 2020.
I had sexual intercourse with a male friend on February 21 and took emergency contraception.
I experienced bleeding for three days starting February 28.
On March 13, I took a pregnancy test which showed negative results.
I did not have my period in March.
Throughout early March to April, my husband and I were actively trying to conceive.
During a visit to the obstetrician on April 6, a pregnancy test also showed negative results.
However, on the morning of April 10, I took a home pregnancy test and got one strong line and one faint line.
The doctor estimated my due date to be December 21.
When do you think I conceived?

Erjie, 20~29 year old female. Ask Date: 2021/05/26

Dr. Cao Guotao reply Obstetrics and Gynecology

Hello, it should not be the one on February 21, but rather conception likely occurred at the end of March.
Wishing you good health.

Reply Date: 2021/05/26

More Info

To determine when you conceived, we need to analyze your menstrual cycle and the events you described. Based on the information you provided, your last menstrual period (LMP) began on February 10, 2020. You had unprotected intercourse on February 21 and took emergency contraception afterward. You experienced some bleeding from February 28 for three days, which could be a side effect of the emergency contraception or an early sign of pregnancy.

You mentioned that you took a pregnancy test on March 13, which was negative, and continued to have unprotected intercourse with your husband throughout March. However, you did not have a menstrual period in March, which is significant. On April 6, you again tested negative for pregnancy at the doctor's office, but by April 10, you received a positive result with one line being faint and the other clear.

Given that your doctor estimated your due date as December 21, 2020, we can calculate your estimated conception date. Typically, pregnancy is calculated from the first day of your last menstrual period, which in your case is February 10. The average gestation period is about 40 weeks (280 days) from the LMP. Therefore, if we count back from your due date of December 21, 2020, we arrive at an estimated conception date around March 28, 2020.

This timeline suggests that the positive pregnancy test you received on April 10 likely indicates that you conceived around the end of March, which aligns with the fact that you did not have a menstrual period in March. The faint line on your test could indicate that it was still early in your pregnancy, and hormone levels (hCG) were just beginning to rise.

It is also important to note that the timing of ovulation can vary from cycle to cycle, and while many women ovulate approximately 14 days before their next period, this is not a strict rule. Factors such as stress, illness, and hormonal imbalances can affect ovulation timing.
In summary, based on your menstrual history and the timing of your positive pregnancy test, it is likely that you conceived around the end of March 2020. If you have further questions or concerns about your pregnancy or fertility, it is always best to consult with your healthcare provider for personalized advice and guidance.

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