The gestational period is calculated from which reference point?

• A. Date of conception
• B. First day of the last menstrual period
• C. Ovulation date
• D. Implantation date

Answer: (B)

Gestational age is counted from the first day of the last menstrual period. This provides a consistent starting point because pregnancy begins before conception, and ovulation typically occurs about two weeks after that day in a typical cycle, making a full term about 40 weeks from LMP (roughly 38 weeks from conception). The exact date of conception is often unknown and varies with cycle length, while implantation happens later and is less reliable for dating. So, using the first day of the last menstrual period standardizes how we measure fetal development and due dates.