Pregnancy Confirmation and Estimated Conception Dates

Pregnancy Test and Conception Date

Hello Doctor, I have confirmed my pregnancy and would like to ask about my last menstrual period, which was at the end of August last year.
I had sexual intercourse on September 19, 24, 26, and 28, as well as on October 3 and 5.
On October 10, I visited a clinic due to vaginal inflammation, and the pregnancy test result was negative.
However, during a follow-up appointment on October 17, I was confirmed to be pregnant.
I found articles online stating that if a pregnancy test is negative more than 14 or 18 days after intercourse, pregnancy can be ruled out.
The date 18 days before October 10 is September 22, and 14 days before October 10 is September 26.
Does this mean that all sexual intercourse prior to September 26 can be ruled out as the conception date? Additionally, the ultrasound estimated my due date to be September 30.
When might the conception have occurred based on the sexual encounters? Thank you for your explanation, Doctor.

Da C, 30~39 year old female. Ask Date: 2023/05/19

Dr. Huang Yuande reply Obstetrics and Gynecology

1.
Assuming that the menstrual cycle is regular, typically 28 days or a fixed number of days (such as 32 days), ovulation occurs around 14 days before the next period.
Adding 1 to 2 days before and after this date defines the fertile window.
2.
Therefore, if the estimated due date is September 30, conception is likely to have occurred around January 6.

Reply Date: 2023/05/19

More Info

To determine the estimated conception date and understand the implications of your pregnancy confirmation, we need to analyze the information provided regarding your menstrual cycle and sexual activity.

Based on your last menstrual period (LMP) at the end of August, we can estimate your ovulation date. Typically, ovulation occurs about 14 days after the first day of your last menstrual period, assuming a regular cycle. If your cycle is around 28 days, ovulation would likely have occurred around September 14. However, if your cycle varies, ovulation could occur earlier or later.
You mentioned having sexual intercourse on September 19, 24, 26, and October 3 and 5. If we consider the timing of ovulation, the most likely window for conception would be around the time of ovulation, which is September 14, plus a few days, as sperm can survive in the female reproductive tract for up to five days. Therefore, sexual intercourse on September 19 and possibly September 24 could be potential conception dates.

Regarding the negative pregnancy test on October 10, it is important to note that testing too early can yield false negatives. If you ovulated later than expected, it could explain why the test was negative at that time. The general guideline is to wait at least 14 days after ovulation to test for pregnancy, which aligns with your timeline. If you ovulated around September 14, then testing on October 10 would be appropriate, and a positive result would confirm pregnancy.

The ultrasound estimated due date of September 30 suggests that the conception likely occurred around early to mid-September. This aligns with the sexual activity you had on September 19 and 24. Therefore, it is reasonable to conclude that one of these dates could be the likely conception date.

In summary, based on your menstrual cycle and the timing of sexual intercourse, it is plausible that conception occurred around September 19 or 24. The negative pregnancy test on October 10 does not rule out these dates, as it may have been too early to detect pregnancy.
For further confirmation and peace of mind, you may consider discussing with your healthcare provider about the possibility of a dating ultrasound, which can provide more accurate information regarding your gestational age and estimated due date. Additionally, if there are any concerns about the timing of conception or paternity, a DNA test can be conducted after the baby is born.

In conclusion, understanding your menstrual cycle, ovulation timing, and the window of fertility is crucial in estimating conception dates. Always consult with your healthcare provider for personalized advice and to address any concerns regarding your pregnancy.

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