From the Research
Based on a last menstrual period (LMP) of January 26,2025, the estimated due date (EDD) would be November 2,2025. This calculation uses Naegele's rule, which adds 7 days to the first day of the last menstrual period and then counts forward 9 months. The formula works because a typical pregnancy lasts approximately 280 days or 40 weeks from the start of the last menstrual period. This method assumes a regular 28-day menstrual cycle and that ovulation occurred on day 14 of the cycle. If your cycles are significantly longer or shorter than 28 days, or if you know your ovulation date was different, the EDD might need adjustment. During prenatal care, this initial EDD calculation may be refined based on ultrasound measurements, particularly those done in the first trimester which provide the most accurate dating, as seen in studies such as 1. Remember that only about 5% of babies are actually born on their estimated due date, with most births occurring within two weeks before or after this date. It's also worth noting that while the provided studies discuss various aspects of pregnancy and ultrasound use, such as 2, 3, 4, and 5, the calculation of the EDD based on LMP remains a fundamental approach in obstetrics. However, for the most accurate estimation, especially in cases where the LMP is uncertain or the cycle length varies significantly, ultrasound dating, as discussed in 1, becomes crucial for refining the EDD to ensure the best possible outcomes in terms of morbidity, mortality, and quality of life.