Pregnancy Testing and Estimated Conception Dates

Pregnancy Testing and Conception Dates Inquiry

I apologize for the question, but I would like to consult a physician.
My menstrual cycle has been very regular for the past year.
The app indicated that my ovulation period was on February 7, and I had sexual intercourse on that day (without a condom and no ejaculation inside).
Another instance was on February 17 (without a condom and external ejaculation).
The first day of my menstrual cycle in January was January 25, and I was supposed to get my period on February 21, but it did not come.
The next day, on February 22, I bought a pregnancy test and used it in the afternoon (not with morning urine), which resulted in one line.
Today, February 28, I am a week late and bought another pregnancy test, which showed two lines (one dark and one faint, but not too faint; both lines were clearly visible).
I would like to ask: which date is more likely to be the conception date, February 7 or February 17? If it was February 7, I should have been able to detect it by February 22; could it be that the urine concentration was insufficient at that time? Or is the chance greater for February 17? Additionally, I wonder if an ultrasound can help estimate the conception date.
Thank you for your response, and I wish you well.

Xiong, 30~39 year old female. Ask Date: 2022/02/28

Dr. Zhang Kunmin reply Obstetrics and Gynecology

Hello, based on your description of symptoms, it is likely that conception occurred around February 7th.
There are many factors that can interfere with the accuracy of a pregnancy test.
Additionally, ultrasound calculations for the date of conception also have a certain margin of error.
Thank you! Wishing you peace and health.
Dr.
Zhang

Reply Date: 2022/02/28

More Info

To determine the estimated conception date and understand the implications of pregnancy testing, it's essential to consider several factors, including the timing of ovulation, the nature of sexual intercourse, and the sensitivity of the pregnancy test used.

Based on your menstrual cycle, which began on January 25, and the ovulation app indicating February 7 as your ovulation day, it is likely that conception occurred around that time. Sperm can survive in the female reproductive tract for up to five days, so if you had unprotected intercourse on February 7, it is plausible that conception could have occurred shortly after. The second instance of unprotected intercourse on February 17, while still possible for conception, is less likely to be the primary date of conception since it is further away from the ovulation window.

Regarding your pregnancy test results, the fact that you tested negative on February 22, but positive on February 28, could be attributed to several factors. The most likely explanation is that the hormone hCG (human chorionic gonadotropin), which is produced after conception, may not have reached detectable levels in your urine on February 22. This can happen if the test is taken too early or if the urine is diluted, as you mentioned using an afternoon sample rather than the first morning urine, which is typically more concentrated.
The presence of two lines on your pregnancy test, with one being faint, indicates that you are indeed pregnant, but the concentration of hCG may still be increasing. It is common for hCG levels to vary in early pregnancy, and a faint line can indicate that you are in the early stages of pregnancy.
As for ultrasound examinations, they can provide a more accurate estimation of gestational age and, consequently, the likely date of conception. An ultrasound can measure the size of the gestational sac or the embryo, which can help determine how far along you are. Generally, the earlier the ultrasound is performed, the more accurate it is in estimating gestational age.
In summary, while the most likely date of conception is February 7, the possibility of conception on February 17 cannot be entirely ruled out. The negative test on February 22 suggests that it was too early to detect pregnancy, while the positive test on February 28 confirms that you are pregnant. For the most accurate assessment of gestational age and to estimate the conception date more precisely, an ultrasound would be beneficial.
If you have any further questions or concerns, especially regarding your health and the progress of your pregnancy, it is advisable to consult with a healthcare provider who can offer personalized guidance and support.

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Hello, the date of conception is usually estimated accurately through ultrasound at around 8 to 9 weeks of pregnancy. Based on your description, it is difficult to make an accurate calculation and explanation. Thank you! Wishing you peace and health, Dr. Zhang.

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