Hi,
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If your expected due date is in 5th December, 2011 (completion of 40 weeks of gestation), then your probable conception dates (based on regular menstrual cycle of 28-30 days) would lie between March 10th â March 20th, 2011. For further clarifications, and discussion visit your doctor/gynecologist. You can also request for a dating scan to be done to know your probable conception date.
Take care.