Possible Conception Dates: A Guide for Women

Inquire about the possible date of conception?

The last menstrual period was on July 7, with a regular cycle of 26-28 days, so the next period was expected on August 3.
Intercourse occurred on July 13, July 19, July 24, and July 27, all with ejaculation inside.
Emergency contraception was taken the day after the intercourse on July 24.
A pregnancy test on July 31 showed two lines indicating pregnancy.
I would like to know the possible conception date.
On September 2 and September 4, ultrasounds performed by different doctors indicated a gestational age of 7 weeks, which is smaller than the actual gestational age.
One doctor suggested that conception may have occurred later.
Is it possible that conception occurred on July 24 or July 27? Since it was with an ex-boyfriend, it is difficult to determine, or would it be better to do prenatal genetic testing? The ultrasound on September 4 indicated that there might have originally been twins, but the other gestational sac did not develop.
Could the presence of twins have caused the smaller gestational age?

Niming, 20~29 year old female. Ask Date: 2020/09/04

Dr. Cao Guotao reply Obstetrics and Gynecology

Hello, on July 31, two lines indicated pregnancy.
The possible conception date is around July 15.
The ultrasound will be monitored for now.
Wishing you good health.

Reply Date: 2020/09/04

More Info

Understanding possible conception dates can be quite complex, especially when considering the variability of menstrual cycles and the timing of ovulation. Based on the information provided, let's break down the details to better understand your situation.

Menstrual Cycle and Ovulation
Your last menstrual period (LMP) started on July 7, and you mentioned that your menstrual cycle is regular, ranging from 26 to 28 days. This means that your next expected period would likely be around August 3. Ovulation typically occurs about 14 days before the start of your next period. Therefore, if we assume a 28-day cycle, ovulation would likely occur around July 21. If your cycle is on the shorter side (26 days), ovulation could occur as early as July 19.

Possible Conception Dates
You engaged in sexual intercourse on July 13, July 19, July 24, and July 27. The timing of these encounters in relation to your ovulation is crucial for determining possible conception dates:
1. July 13: This is before your expected ovulation, so the likelihood of conception is low.

2. July 19: This is very close to your ovulation window, making it a possible conception date.

3. July 24: This is a few days after ovulation, but sperm can survive in the female reproductive tract for up to five days. Therefore, if you ovulated later than expected, conception could still occur from this encounter.

4. July 27: This is likely too late for conception if ovulation occurred around July 21, but again, if ovulation was delayed, there is a slight chance.

Given that you received a positive pregnancy test on July 31, it is likely that conception occurred around July 19 or July 24, especially since you mentioned that you took emergency contraception after the encounter on July 24.

Ultrasound Findings and Gestational Age
Regarding the ultrasound findings on September 2 and September 4, which indicated a gestational age of 7 weeks but seemed smaller than expected, it’s important to note that early ultrasounds can sometimes show variability in gestational age due to several factors, including the timing of ovulation and conception. If you conceived later than the estimated ovulation date, this could explain the discrepancy.

Twin Pregnancy Considerations
You mentioned that there was initially a possibility of twins, but one embryo did not develop. In twin pregnancies, especially in the early stages, it is not uncommon for one embryo to be absorbed or to stop developing. This can sometimes lead to a smaller gestational size if the surviving embryo is affected by the presence of the other.

Conclusion and Recommendations
In summary, the most likely conception dates based on your cycle would be July 19 or July 24. If you are uncertain about the paternity of the child, a prenatal paternity test can be conducted, but it is typically recommended to wait until after the first trimester for more accurate results.

If you have further concerns about your pregnancy, including the health of the fetus or any complications, it is advisable to consult with your healthcare provider for personalized guidance and monitoring. They can provide you with the best advice based on your specific circumstances and medical history.

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