Most women don't realise they are pregnant until they miss their period once or twice in a row. However the countdown to your pregnancy starts from the first day of your last menstrual cycle just before conception. That means you are considered to be pregnant even before you conceive. There is a logical explanation behind this. To calculate your expected delivery date the days are counted from the first day of your last menstrual cycle. Conception happens about 14 days after your periods start precisely when you start to ovulate. Remember each month you carry a fair chance approximately 25%