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For most expectant mothers, one of the first and most frequently asked questions is “How many weeks pregnant am I?” All pregnancy-related calculations are based on the assumption that a normal pregnancy lasts approximately 40 weeks, which equals 9 months and 10 days. However, not every pregnancy ends exactly at week 40. Even when there are no medical problems and pregnancy progresses normally, some babies may be born earlier, while others may arrive later.
Knowing how many weeks pregnant you are is essential for tracking fetal development, planning prenatal care, and preparing for delivery. From a medical perspective, pregnancy is followed week by week, not month by month. Ultrasound examinations and routine check-ups rely on gestational age to assess whether the baby’s growth and development are progressing as expected.
For women with regular menstrual cycles, pregnancy calculation is based on the first day of the last menstrual period (LMP). A menstrual cycle begins on the first day of bleeding and ends on the first day of the next period. While cycle length varies among women, it is commonly accepted as an average of 28 days, with a normal range between 21 and 35 days.
During each cycle, hormonal changes cause one egg to mature in the ovaries. Around the middle of the cycle—often near day 14—this egg is released during ovulation. If the egg meets sperm during this time, fertilization occurs and pregnancy begins.
Although fertilization happens days after the start of the menstrual cycle, the exact moment of fertilization cannot be determined with certainty. For this reason, doctors do not calculate pregnancy based on the date of intercourse or fertilization. Instead, pregnancy is calculated from the first day of the last menstrual period, which is a clearly identifiable and reliable reference point.
Calculating pregnancy based on the date of sexual intercourse is not considered a reliable method. Sperm can survive in the female reproductive tract for up to 72 hours, and ovulation does not always occur exactly on day 14 of the cycle.
Even in planned pregnancies, fertilization may occur one or more days after intercourse. Therefore, knowing the intercourse date alone is not sufficient to accurately determine gestational age or due date. Medical professionals continue to rely on the last menstrual period or ultrasound measurements for accurate pregnancy dating.
If you know the first day of your last menstrual period, pregnancy weeks can be calculated by counting the number of weeks from that date to today. This method allows you to estimate:
For example, if your last menstrual period started on May 7, pregnancy week calculation begins from that date, not from the date of ovulation or intercourse.
Pregnancy calculation differs slightly in IVF pregnancies, as the exact date of embryo transfer is known. However, IVF pregnancies are still calculated in a way that aligns with natural pregnancy timelines.
In IVF:
This standardized approach ensures that IVF pregnancies are followed using the same medical framework as spontaneous pregnancies.
Pregnancy calculations can be confusing, especially since pregnancy is often described in months rather than weeks. Medically, pregnancy is divided into three trimesters, each lasting approximately three months.
A pregnancy calculation chart helps expectant mothers visualize:
Such charts are commonly used in pregnancy calculators and during prenatal visits.
The most widely used method for estimating the due date is based on the last menstrual period. The calculation is performed by:
This method provides an estimated due date, but variations of up to ±2 weeks are considered normal. Ultrasound measurements may sometimes differ from calculations based on the last menstrual period. When discrepancies occur, doctors may rely more on ultrasound dating, especially in early pregnancy.
Labor can normally occur anytime between 38 and 42 weeks. Going beyond 42 weeks is generally not recommended, as it may increase risks for both mother and baby.
No due date calculation method is 100% accurate. Pregnancy week calculations provide an estimate, not a guaranteed delivery date. Although many theories exist regarding what triggers labor—such as physical activity, sexual intercourse, or certain foods—there is no definitive scientific evidence confirming these methods.
For this reason, pregnancy follow-up should always be based on regular medical check-ups rather than a fixed date. Each baby ultimately determines when it is ready to be born.
For all your questions, you can contact us at 444 39 49.
Pregnancy weeks are calculated from the first day of your last menstrual period. This method is used worldwide by healthcare professionals.
In IVF pregnancies, the embryo transfer date is used. Pregnancy is considered to be 4 weeks at the time of a positive β-hCG test, and the due date is calculated by adding 38 weeks to the transfer date.
This method is not reliable because ovulation and fertilization timing vary, and sperm can survive for several days.
Pregnancy is divided into three trimesters: weeks 1–13, 14–27, and 28 until birth.
No. The due date is an estimate. Normal delivery can occur between 38 and 42 weeks.
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