A pregnancy is calculated as 40 weeks long, and the first day of your pregnancy begins on the first day of your last menstrual period (LMP).
Most women conceive two weeks after their LMP. Your baby, therefore, will only have lived 38 weeks by the time your pregnancy has reached the 40-week mark.
This calculation makes sense because you know which day you started bleeding, but you do not know with 100 percent accuracy the day you ovulated. And even if you do, do you know with certainty the date you conceived or the date sperm and egg actually met?
Counting weeks like birthdays
The weeks in pregnancy are counted like birthdays. Just as we say that a child turns one 1 after it has lived one year, we say that a woman is pregnant for 1 week after she has completed 1 week from the day of her last menstrual period (LMP).
Why 3 Trimester
Usually, most women’s pregnancies are around nine months long, which are divided into three trimesters. Each trimester is three months long. Defining the trimesters in pregnancy helps in explaining your body changes.
First trimester: starts from the first day of your pregnancy to week 13, day 6. Other than the excitement of knowing that you’re pregnant, you may develop pregnancy symptoms such as morning sickness, nausea, and feeling exhausted.
Second trimester: starts from week 14 to week 27, day 6. You may feel much better in this trimester because the pregnancy symptoms are likely to lessen day by day. Another major change is that your bump is starting to grow bigger.
Third trimester: starts from week 28 to the day the baby is born. You’ll probably have tiredness and fatigue because Your Baby is growing very fast and this drains your energy.
Fourth trimester: starts from the day Your Baby was born to 3 months later. It is defined as the bonding period between you and your little one.
Is my due date accurate?
Actually, your due date is just an estimate of when you will give birth, calculated from your LMP. Though most babies arrive between week 38 to 41, another 5% are born exactly on their due date.