Estimating Your Conception Date: A Guide for Women Struggling to Conceive

Please help me calculate the exact date of conception?

Hello Doctor, I have been unable to conceive for a long time and I am currently troubled by some situations.
I am confused about the size of the gestational sac and whether it corresponds to the weeks of pregnancy.
I have done some research and I am unsure about my conception date.
My menstrual cycle is approximately 24 days, lasting about 5-7 days.

My menstrual dates are as follows:
- 2019/12/13 to 12/19
- 2020/1/4 to 1/10
- 2020/1/27 to 2/1
- 2020/2/22 to 2/26
I had intercourse on 2/16, 2/29, 3/1, and 3/13.
On 3/2, I went for a follicle scan and the doctor said the endometrium was 1.3 cm and the follicle was only 0.9 cm, indicating that the egg was too small and would need a few more days to mature (but it was estimated to be my ovulation day).
On 3/7, the doctor said the follicle could no longer be seen, indicating ovulation had occurred.

My expected menstrual period on 3/17 did not arrive.
On 3/24, I took a pregnancy test and saw two lines, both of which were equally dark.
The LH test showed a second line that was darker than the control line.
On 3/24, I also did a blood test for HCG, which was 833.
On the same day, the doctor measured the gestational sac at 0.75 cm, describing it as a dark blob (the doctor said it was just amniotic fluid), estimating it to be about 5 weeks along, and advised to check for a heartbeat in 3 weeks.
1.
Can you help me estimate my conception date? How long has it been since the actual conception based on the size of the gestational sac?
2.
The doctor mentioned the gestational sac is 4-5 weeks along and the HCG levels suggest that I may have actually conceived about a month ago?
3.
Is it still possible that I conceived on 2/29? However, the follicle was still small on 3/2?
4.
Could it be that I conceived on 2/16 and then had my period afterward? The app indicates that ovulation day was several days ago, with the expected ovulation day being 2/8.
5.
Is it possible that my baby is developing too quickly? Is there a problem?
6.
Is the size of the gestational sac measured by its longest length or its shortest width? Currently, aside from feeling a bit dizzy and experiencing premenstrual syndrome, I have no bleeding symptoms.
I am very confused and sincerely ask for your help.

883, 30~39 year old female. Ask Date: 2020/03/26

Dr. Wu Xianghui reply Obstetrics and Gynecology

If the estimated gestational age is 5 weeks, conception likely occurred between mid-February and the end of the month.
For accurate dates and other related concerns, please consult an obstetrics and gynecology clinic for evaluation.

Reply Date: 2020/03/26

More Info

Estimating your conception date can be quite complex, especially for women who have irregular menstrual cycles or are experiencing difficulties in conceiving. Based on the information you've provided, let's break down your situation and address your questions systematically.

1. Understanding Your Menstrual Cycle: You mentioned that your menstrual cycle averages around 24 days, with periods lasting 5-7 days. This shorter cycle can lead to more frequent ovulation, which may affect your conception timing. Typically, ovulation occurs about 14 days before your next period starts. However, with a 24-day cycle, ovulation could occur as early as day 10 or 11 of your cycle.
2. Estimating Your Conception Date: Given your menstrual history, your last period started on February 22, 2020. If we assume ovulation occurred around February 10-12, then conception could have happened around that time. However, you also mentioned having sexual intercourse on February 16, February 29, and March 1. If ovulation was delayed or if you had a follicle that matured earlier than expected, it's possible that conception could have occurred from any of these encounters.
3. Embryo Development and HCG Levels: You reported an HCG level of 833 on March 24, which is consistent with early pregnancy. The presence of a gestational sac measuring 0.75 cm suggests that you are approximately 5 weeks pregnant. HCG levels typically double every 48-72 hours in early pregnancy, so your levels should be monitored to ensure they are rising appropriately.

4. Possible Conception Dates: Regarding your question about the possibility of conceiving on February 29, it is plausible if ovulation occurred later than expected. The fact that your follicle was small on March 2 suggests that ovulation may have been delayed, which can happen due to various factors such as stress or hormonal fluctuations.
5. Understanding Menstrual Irregularities: It’s also worth noting that some women can experience what is known as "breakthrough bleeding," which can occur even when they are pregnant. This could explain why you might have had a period-like experience after conception.
6. Measuring the Gestational Sac: The size of the gestational sac is typically measured in its longest dimension, and it is a key indicator of the gestational age. The size you mentioned (0.75 cm) aligns with what would be expected at around 5 weeks of gestation.

7. Symptoms and Concerns: Feeling dizzy and experiencing premenstrual symptoms can be common in early pregnancy due to hormonal changes. However, if you experience any severe symptoms or bleeding, it is crucial to consult your healthcare provider immediately.

In conclusion, while it is challenging to pinpoint the exact date of conception, the information you provided suggests that it likely occurred around mid-February, with the possibility of conception from any of the sexual encounters you mentioned. It is essential to continue monitoring your HCG levels and follow up with your healthcare provider for ultrasounds and further assessments to ensure a healthy pregnancy. If you have any concerns or experience unusual symptoms, do not hesitate to seek medical advice.

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