When Did I Conceive? Pregnancy Timing and Testing

When did conception occur?

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.
A pregnancy test on March 13 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 that showed one strong line and one faint line.
The doctor estimated my due date to be December 21.
Could you please tell me when I might have conceived? Additionally, I would like to ask if the ultrasound on May 7, which showed 8 weeks and 1 day, could indicate that conception occurred during the encounter on February 21?

Erjie, 20~29 year old female. Ask Date: 2021/05/27

Dr. Cao Guotao reply Obstetrics and Gynecology

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

Reply Date: 2021/05/27

More Info

To determine when you conceived, we need to consider several factors, including your menstrual cycle, ovulation timing, and the results of your pregnancy tests.

Based on your information, your last menstrual period (LMP) started on February 10, 2020. Typically, ovulation occurs about 14 days after the start of your last menstrual period in a regular cycle. Given that your cycle is regular, ovulation would likely have occurred around February 24, 2020. If you had unprotected intercourse on February 21 and took emergency contraception afterward, it is possible that the emergency contraception could have prevented ovulation or fertilization.

You mentioned experiencing light bleeding from February 28 for three days, which could be implantation bleeding, but it is also possible that it was just a side effect of the emergency contraception. The pregnancy test on March 13 was negative, which suggests that you were not pregnant at that time. However, you did not get your period in March, which could indicate a delay due to various factors, including the use of emergency contraception.

When you took a home pregnancy test on April 10 and received a faint positive result, it suggests that you might have conceived around the time of ovulation, which would align with the timing of your last menstrual period. The ultrasound on May 7 showing 8 weeks and 1 day of gestation would place your estimated conception date around the end of February or early March, which is consistent with the ovulation date calculated from your LMP.

To summarize, while the exact date of conception can be difficult to pinpoint, it is likely that you conceived around late February to early March. The ultrasound results further support this timeline, indicating that the pregnancy is consistent with conception occurring after February 21, especially considering the negative pregnancy tests prior to April.

In terms of pregnancy dating, healthcare providers typically calculate gestational age from the first day of your last menstrual period, which is why your estimated due date is December 21. This method assumes a 28-day cycle, with ovulation occurring approximately 14 days after the LMP. Therefore, if your cycle is longer or shorter, adjustments may be made based on ultrasound findings.

It's important to continue regular prenatal care and follow up with your healthcare provider for any concerns or questions regarding your pregnancy. They can provide personalized guidance based on your medical history and current health status.

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