Determining Your Conception Date: Key Factors and Insights - Obstetrics and Gynecology

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Determining the conception date can be a complex process, influenced by various factors including menstrual cycle regularity, timing of ovulation, and the nature of sexual intercourse. In your case, you have provided a detailed account of your menstrual cycle and sexual activity, which allows for a more accurate assessment.

Firstly, let's consider your menstrual cycle. You mentioned that your cycles have been consistently 28 to 29 days long, with your last menstrual period starting on January 9. This regularity is crucial because it helps predict ovulation. Typically, ovulation occurs about 14 days before the start of your next period. Given your cycle length, ovulation would likely have occurred around January 23.
You had sexual intercourse on January 21, which is just two days before your estimated ovulation date. This timing is significant because sperm can survive in the female reproductive tract for up to five days. Therefore, intercourse on January 21 could indeed lead to conception if ovulation occurred shortly after.

On January 26, you had another sexual encounter, but you indicated that this was not a full intercourse event, as it involved only a few thrusts followed by oral ejaculation. While it is theoretically possible for pre-ejaculate fluid to contain sperm, the likelihood of conception from this encounter is significantly lower compared to a full intercourse event, especially if ejaculation did not occur inside the vagina.

Now, regarding your basal body temperature (BBT) readings, they provide additional insight into your ovulation. You recorded a rise in temperature starting from January 18, peaking around January 28. A sustained increase in BBT typically indicates that ovulation has occurred. The rise in temperature after ovulation is due to the hormone progesterone, which is released after the egg is released from the ovary. The fact that your temperature remained elevated after January 23 supports the idea that you likely ovulated around that time.

Given all this information, it is reasonable to conclude that the sexual encounter on January 21 is more likely to have resulted in conception than the encounter on January 26. The timing aligns closely with your ovulation, and the nature of the second encounter diminishes its potential for leading to pregnancy.

As for the pregnancy test you took on February 9, which yielded a positive result, this aligns with the expected timeline for detecting pregnancy. Typically, home pregnancy tests can reliably detect pregnancy about one week after a missed period, which in your case would be around the time you tested.

In summary, while it is theoretically possible for conception to occur from either encounter, the evidence strongly suggests that the encounter on January 21 is the more likely date of conception. The combination of your menstrual cycle regularity, ovulation timing, and the nature of the sexual activities all point toward this conclusion. If you have further questions or concerns about your pregnancy or conception, it is advisable to consult with a healthcare provider for personalized guidance and support.