Calculating Conception Date: Pregnancy Timing and Factors

Please help me estimate my conception date, doctor?

Hello Dr.
Huang: My menstrual cycle started on February 3, 2018, with an uncertain cycle length of about 25-28 days.
My periods typically last around 8-10 days, and I have polycystic ovary syndrome (PCOS).
I have been trying ovulation induction therapy with my boyfriend for nine years, but I have never been pregnant.
I continued taking ovulation medication in February, and on February 24, my obstetrician said I would receive an ovulation trigger injection that day.
On February 25 and 26, I had unprotected intercourse with my boyfriend.
On March 12, I had unprotected sexual intercourse with someone else.
On March 16, I used a home pregnancy test, which showed two strong lines.
A visit to the obstetrician also confirmed pregnancy, but the gestational sac could not be seen initially.
On March 19, a 0.6 cm gestational sac was observed, and on March 30, a heartbeat was detected.
On April 7, the measurement was 0.87 cm, and the ultrasound indicated 6 weeks and 6 days of gestation.
Dr.
Huang, could my baby have been conceived during the encounter on March 12? Given that I had unprotected intercourse with my boyfriend for nine years without conceiving, it feels overwhelming that this unexpected pregnancy occurred after a single encounter.
The timeline is concerning because the sexual activity on March 12 was only four days before I tested positive on March 16, and the gestational sac was seen just seven days later on March 19.
Is this possible? Thank you for your response, Dr.
Huang.

Yilian, 30~39 year old female. Ask Date: 2018/04/09

Dr. Huang Jianzhong reply Obstetrics and Gynecology

The first day of the menstrual period was on February 3, 2018, with an uncertain cycle of approximately 25-28 days.
The menstrual flow lasts about 8-10 days each time, and I have polycystic ovary syndrome (PCOS).
I have been trying ovulation induction therapy with my boyfriend for nine years but have never been pregnant.
I continued taking ovulation medication in February, and on February 24, my obstetrician said I would receive an ovulation trigger injection.
On February 25 and 26, I had unprotected intercourse with my boyfriend.
On March 12, I had unprotected sexual intercourse with someone else.
On March 16, I used a home pregnancy test, which showed two strong lines.
A visit to the obstetrician confirmed pregnancy, but the gestational sac was not visible.
On March 19, a 0.6 cm gestational sac was seen, and on March 30, a heartbeat was detected.
On April 7, the measurement was 0.87 cm, and a heartbeat was heard (the ultrasound indicated 6 weeks and 6 days).

Dr.
Huang, could my baby have been conceived from the encounter on March 12?
Answer: It is unlikely that the pregnancy resulted from the encounter on March 12, as I had unprotected intercourse with my boyfriend for nine years without conceiving.
The unexpected pregnancy occurred after the first deviation from our routine.
I feel helpless because the sexual encounter on March 12 was only four days before I tested positive on March 16, and the gestational sac was seen just seven days later on March 19.
Is that possible?
Answer: It is not very likely.

Reply Date: 2018/04/09

More Info

To calculate the conception date and understand pregnancy timing, it's essential to consider several factors, including the menstrual cycle, ovulation, and the timing of sexual intercourse. In your case, you have a history of irregular menstrual cycles due to polycystic ovary syndrome (PCOS), which can complicate the calculation of ovulation and conception dates.

Typically, the first day of your last menstrual period (LMP) is used as a reference point for calculating pregnancy weeks. In your case, you mentioned that your LMP was on February 3, 2018, and your cycle length varies between 25 to 28 days. This variability can affect when you ovulate, which is crucial for determining the conception date.

Based on your account, you received an ovulation trigger shot on February 24, which would likely induce ovulation within 24 to 36 hours. Therefore, ovulation would have occurred around February 25 or 26. Engaging in unprotected intercourse on these dates would be the most likely window for conception.
You also mentioned having sexual intercourse on March 12, which is quite a bit later than your ovulation window. Given the timing, it is highly unlikely that conception occurred from the March 12 encounter. Sperm can survive in the female reproductive tract for up to five days, but since your ovulation window was around February 25-26, the sperm from the March 12 encounter would not have been viable for fertilization.

The positive pregnancy test on March 16, just four days after the March 12 encounter, further supports that conception likely occurred earlier. The ultrasound on March 19 showing a gestational sac and the subsequent ultrasound on April 7 confirming a heartbeat at 6 weeks and 6 days also align with conception occurring around the end of February, not in March.

In summary, it is most probable that your conception occurred shortly after your ovulation on February 25 or 26, following the ovulation trigger shot. The timing of your sexual encounters suggests that the pregnancy is a result of the intercourse that took place around your ovulation date rather than the later encounter on March 12.

Given your history of trying to conceive for nine years without success, this unexpected pregnancy may feel overwhelming. It's important to discuss your feelings and any concerns with your healthcare provider, who can offer support and guidance tailored to your situation. Regular prenatal care is crucial, especially considering your PCOS, to monitor the health of both you and your baby throughout the pregnancy.
If you have any further questions or need clarification on any points, please feel free to ask.

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