Conception Dates: A Guide for Expecting Mothers

What is the date of conception?

Hello Doctor, I am quite troubled about whether the size of the gestational sac corresponds with the weeks of gestation.
I have done some research and am confused about the date of conception.
My menstrual cycle is approximately 24 days, lasting about 5-7 days.

- From December 13 to December 19, 2019, my period lasted 7 days.
- From January 4 to January 10, 2020, my period lasted 7 days.
- From January 27 to February 1, 2020, my period lasted 6 days.
- From February 22 to February 26, 2020, my period lasted 5 days (on February 22, I had only some brown spotting with a little red blood; from February 23 to February 25, the flow was normal; it decreased on February 26 and was completely gone by February 27).
I had intercourse on February 16, February 29, March 1, and March 13.
On March 2, I went for a follicle scan, and the doctor said the follicle was only 0.9 cm and the endometrium was 1.3 cm, indicating that the egg was too small and needed a few more days to mature (but it was estimated to be around my ovulation day).
On March 7, I went for another scan, and the doctor said the follicle was no longer visible, indicating ovulation had occurred.

My period was expected on March 17 but did not arrive.
On March 24, I took a pregnancy test, which showed two lines, with the second line significantly darker than the control line.
On the same day, I had a blood test for HCG, which was 8334 (tested at 7 PM).
The doctor then measured the gestational sac at 0.75 cm, estimating it to be around 5 weeks.
On March 26, an abdominal ultrasound showed the gestational sac at 1.08 cm, but there was no heartbeat yet.
On March 27, my HCG level was 20675 (tested at 7 PM).
1.
Based on this information, can I estimate my date of conception? How long has it been since the actual conception?
2.
The doctor mentioned it was approximately 4-5 weeks based on the blood test information, but it seems like it has already been about a month since conception?
3.
Is it still possible that conception occurred on February 29 or March 1? However, the follicle was still small on March 2.
Could there have been an early ovulation?
4.
Is it possible to conceive on February 16 and still have a period afterward? The app indicates that ovulation occurred several days earlier, likely on February 8.
Can we rule out February 16?
5.
Or is it that my baby is growing too quickly? Is there a problem? Currently, aside from feeling a bit dizzy and experiencing premenstrual syndrome, I have no bleeding symptoms.
I kindly ask for your help in clarifying these concerns.

ay, 30~39 year old female. Ask Date: 2020/03/30

Dr. Cao Guotao reply Obstetrics and Gynecology

Hello, you likely conceived around March 10.
If you have any further questions, please consult your obstetrician-gynecologist.
Wishing you good health.

Reply Date: 2020/03/30

More Info

Understanding conception dates can be quite complex, especially when considering the variability in menstrual cycles and ovulation timing. Based on the information you've provided, let's break down your questions and clarify the situation regarding your conception date and the development of your pregnancy.

1. Estimating the Conception Date: Given your menstrual cycle history, it appears that your cycle length is around 24-28 days. Ovulation typically occurs about 14 days before your next expected period. If we consider your last menstrual period (LMP) starting on February 22, 2020, ovulation would likely have occurred around February 8, 2020. However, you mentioned engaging in intercourse on February 16, February 29, and March 1. The most likely conception date would be around February 29 or March 1, as sperm can survive in the female reproductive tract for up to five days, making it possible for sperm from intercourse on February 29 to fertilize an egg released during ovulation.

2. Development of the Embryo: The size of the gestational sac (0.75 cm on March 24) corresponds to approximately 5 weeks of gestation, which aligns with the timing of your last menstrual period. The gestational age is typically calculated from the first day of your last menstrual period, which means that by the time you had the ultrasound, you were indeed around 5 weeks pregnant. The embryo develops rapidly in the early weeks, and it is not uncommon for the gestational sac to measure slightly ahead of the expected gestational age based on LMP.

3. Possibility of Conception Dates: It is unlikely that you conceived on February 16 if your ovulation was around February 8. The egg would not have been viable for fertilization by the time of your next period. The ultrasound findings and HCG levels suggest that conception likely occurred closer to the end of February or the beginning of March.

4. Menstrual Cycle and Conception: It is also important to note that it is possible to experience light bleeding or spotting even after conception, which some women mistake for a period. However, if you had a full menstrual period starting on February 22, it is unlikely that you conceived during that cycle. The bleeding you experienced could have been implantation bleeding, which can occur around the time your period is due.

5. Rapid Growth of the Embryo: The growth of the gestational sac and embryo can vary from pregnancy to pregnancy. The measurements you provided indicate that your embryo is developing appropriately for the gestational age. The absence of bleeding and the presence of HCG levels that are rising appropriately are positive signs.

In summary, based on your menstrual cycle and the timing of intercourse, it is most likely that conception occurred around February 29 or March 1. The ultrasound and HCG levels support this timeline. If you have any concerns about your pregnancy or symptoms you are experiencing, it is always best to consult with your healthcare provider for personalized advice and care. They can provide reassurance and monitor your pregnancy to ensure everything is progressing well.

Similar Q&A

Calculating Conception Date Based on Due Date: May 14th Insights

Hello, if the due date is May 14 of this year, the estimated conception date would be around August 21 of the previous year.

Dr. Huang Yiwen reply Obstetrics and Gynecology
Hello, Miss Xiao Xiao: If your menstrual cycle is regular and occurs once a month, then your estimated ovulation date would be around two to three days before or after August 21 of last year.

Calculating Conception Date Based on Due Date: A Guide

If the due date is September 20, the estimated conception date would be around December 27 of the previous year. Currently, you are at 19 weeks of gestation.

Dr. Cao Guotao reply Obstetrics and Gynecology
Hello, it should be around the end of December. Wishing you good health.

Determining Your Pregnancy Date: A Guide for Expecting Mothers

To estimate the date of conception, we can consider the details provided. Your last menstrual period (LMP) started on February 10. Typically, ovulation occurs about 14 days after the start of the last menstrual period, which would be around February 24. You mentioned having sex...

Dr. Huang Yuande reply Obstetrics and Gynecology
The gestational age shown by ultrasound is usually more accurate, so you can count back six weeks from May 7, which may indicate the date of conception.

Calculating Conception Date Based on Due Date: A Guide for Parents

Hello Dr. Tsao, my second child is due on January 15, 2021. My wife and I had intercourse in early March, and when I calculate the date back from 40 weeks, it doesn't seem accurate. Am I overthinking this? Thank you.

Dr. Cao Guotao reply Obstetrics and Gynecology
Hello, this question may be more appropriate for your obstetrics and gynecology department. Wishing you good health.