Verified answer

If you have regular periods and you know when you had sex, they say sperm can take three days to travel through your tubes to meet the egg so the date of conception isn't always the say day you had sex. Also you don't always ovulate exactly 14 days after your period. As long as everyone is healthy I would take the 14 weeks over 11.

Since it's very hard to pinpoint exactly when you conceived, pregnancy is calculated 40 weeks from the first day of your last period. Typically a women ovulates and thus conceives about 2 weeks after this date, which is why you are considered 2 weeks pregnant at that point. A little confusing I know, but they should be able to give you a fairly accurate due date during your first ultrasound if you're concerned about the due date.

Nagele's Rule is the standard method used to predict the length of a pregnancy. If fertilization occurs early in a menstrual cycle, the pregnancy will probably end "early"; if ovulation and fertilization occur later in the cycle, the pregnancy will end late. Because of these normal variations, a pregnancy ending 2 weeks before or 2 weeks after the estimated calculated date of birth is considered well within the normal limit.To calculate the date of birth, count backward 3 calendar months from the first day of the last menstrual period and add 7 days.

Ah, one of my favourite subjects to rant about!

The due date is based on a *very* out of date calculation, which is traditional but doesn't take account of recent advances in scientific knowledge.

The date is always calculated from the first day of a woman's last menstrual period, even if she can be sure she conceived a week after her period, or three weeks after her period. It's the standard practice to count from the date of the last period.

Also growth rates are calculated within a 'normal range'. Your baby's size is within the normal range for someone whose last menstrual period was 14 weeks ago. If you had conceived a week earlier, your baby's size would still be within the normal range.

It gets more complicated: growth is calculated according to a centile curve. Your baby might be on the 50th centile (i.e. bang on average) or on the 25th centile (smaller than average but still within the normal range) or on the 90th centile (bigger than most, but still within the normal range). As long as the baby stays on approximately the same centile all through the pregnancy, no one will get worried. But if a baby goes from the 90th centile to the 10th centile, obviously it's having a growth problem.

And there's something else every pregnant woman should know: your due date is NOT your due date! The average length of a human pregnancy is 8 days AFTER the due date calculated by doctors. So more women will give birth after their due date than before it.

Hope that helps a bit.

because they do not know exactly when you conceived and you have a 2 week give or take due date. so, 2 weeks late or 2 weeks early is normal