Fetal Weeks and Conception Dates: A Guide for Expecting Mothers

Fetal gestational age and conception date?

I hope the doctor can help me clarify the following questions.
I experienced vaginal inflammation and a Candida infection in August and September of 2022.
I am unsure if my physical condition affected this.
By mid-October, I had not gotten my period and took a pregnancy test, which was positive.
My actual last menstrual period was on August 28, 2022.
The doctor informed me that my last menstrual period was on September 17, 2022, and that conception likely occurred around September 30, 2022, with a due date of June 24, 2023.
I would like to clarify the following points:
1.
My actual last menstrual period was on August 28, 2022.
I am concerned that the conception date provided by the doctor does not align with the ovulation dates indicated by my app for this menstrual cycle or the next.
What could explain this discrepancy? Is it due to ultrasound measurement errors or other factors?
2.
If the conception date provided by the doctor is accurate, I would like to know which of the following dates—September 19, 24, 26, 28, or October 3, 5—was most likely the date of intercourse that led to conception.

Niming, 20~29 year old female. Ask Date: 2023/04/30

Dr. Cao Guotao reply Obstetrics and Gynecology

Hello, it is possible to estimate the date of conception using ultrasound; however, it is not possible to determine the exact day around September 30th.
Wishing you good health.

Reply Date: 2023/04/30

More Info

Understanding fetal weeks and conception dates can indeed be confusing for expecting mothers, especially when there are discrepancies in menstrual cycle tracking and medical advice. Let’s break down your questions and clarify the situation based on medical knowledge.

1. Discrepancies in Last Menstrual Period (LMP) and Conception Dates
You mentioned that your last menstrual period (LMP) was on August 28, 2022, while your doctor indicated September 17, 2022, as your LMP. This discrepancy can arise from several factors:
- Irregular Cycles: If your menstrual cycles are not consistently 28 days, this can lead to confusion regarding the LMP. For example, if your cycles vary in length, the estimated ovulation date (which typically occurs about 14 days after the LMP) may not align with the standard calculations.

- Ovulation Timing: The timing of ovulation can also vary. While many women ovulate around day 14 of a 28-day cycle, some may ovulate earlier or later. If you have a shorter cycle, ovulation might occur sooner than expected.

- Medical Estimation: Doctors sometimes use ultrasound measurements to estimate gestational age, which can lead to different conclusions about the LMP and conception dates. Ultrasound is often more accurate in determining gestational age, especially in the first trimester.

- Infections and Health Conditions: Conditions like vaginal infections or yeast infections can sometimes affect menstrual regularity, leading to confusion about the timing of your last period.

2. Determining the Most Likely Conception Date
If we assume your doctor’s estimation of the conception date around September 30, 2022, and you are trying to pinpoint the most likely days of conception from the dates you provided (September 19, 24, 26, 28, and October 3, 5), here’s how to approach it:
- Fertile Window: The fertile window typically spans from about five days before ovulation to one day after. If you ovulated around September 30, then the days leading up to that date (September 24-30) would be the most likely candidates for conception.

- Sperm Viability: Sperm can live inside the female reproductive tract for up to five days. Therefore, intercourse on September 24, 26, or even 28 could potentially lead to conception if ovulation occurred shortly after.

- Tracking Symptoms: If you were tracking ovulation symptoms (like changes in cervical mucus or basal body temperature), this could provide additional clues about when you ovulated.

Conclusion
In summary, the discrepancies in your LMP and conception dates can be attributed to variations in menstrual cycles, ovulation timing, and the accuracy of ultrasound measurements. To clarify your situation, it may be beneficial to have a follow-up appointment with your healthcare provider to discuss these discrepancies and possibly undergo a dating ultrasound if you haven’t already.
As for determining the most likely conception date, focus on the days leading up to your estimated ovulation date, particularly September 24-30. Understanding these factors can help alleviate some of the confusion and anxiety surrounding your pregnancy timeline.
Always remember that every pregnancy is unique, and if you have any concerns, don’t hesitate to reach out to your healthcare provider for personalized advice and reassurance.

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