Exact number of weeks between last menstrual period and expected date of delivery :March 2005

Ans. C: 40 weeksChildbih usually occurs about 38 weeks after conception; i.e., approximately 40 weeks from the last normal menstrual period (LNMP).The World Health Organization defines normal term for delivery as between 37 weeks and 42 weeksEDD is calculated by Naegele's ruleAdd 7 days to the first day of the last period and subtract 3 monthsNaegele's rule is based on 28 days regular cycle.If the cycle is shoer or longer than 28 days, EDD will be corrected and written as corrected EDD.Examples:40 days cycle regularly, to get corrected EDD, add 12 days (40-28) with the EDD calculated from LMP.21 days cycle regularly, to get corrected EDD, subtract 7 days (28-21) with the EDD calculated from LMP.