Tracking your pregnancy stage can be confusing when you're figuring out weeks, months or trimesters. Doctors use your LMP to date your pregnancy because many women don't know which day they ovulated or conceived. Your due date is just a good guess – but it's helpful. So is knowing about pregnancy trimesters and how to translate weeks to months in pregnancy.
How many weeks are there in a pregnancy?
Counting from the first day of your LMP, your pregnancy due date will be calculated on the basis of 40 weeks. However, that doesn't mean that's when you'll have your baby. Your actual date of delivery could be a few weeks before or after your estimated due date.
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How long is each trimester of pregnancy?
There's no official definition, but the trimesters are generally considered to be about three months each. "Trimester" means "three months". As most pregnancies are around nine calendar months long, each pregnancy is divided into three trimesters.
At BabyCenter, you graduate to the second trimester the day you turn 14 weeks pregnant. The third trimester starts the day you turn 28 weeks pregnant.
Dividing your pregnancy into trimesters is just a useful way to describe the changes that are happening in your body:
First trimester (early pregnancy)
Your first trimester lasts from the very beginning of your pregnancy until you're 13 weeks plus six days pregnant. Along with the excitement of discovering that you're expecting, you may feel exhausted and nauseous.
Second trimester (mid-pregnancy)
Your second trimester lasts from when you're 14 weeks to 27 weeks plus six days pregnant. During this trimester, you'll probably feel much better. You may start to bloom, your bump will show, and early pregnancy symptoms will be behind you.
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Third trimester (late pregnancy)
Your third trimester lasts from when you're 28 weeks pregnant until 40 weeks. You'll need extra energy to help your baby's growth spurt, and tiredness will probably return.
You may also hear people talk about the "fourth trimester". This refers to the three months after the birth, when you're bonding with your newborn baby.
Keep in mind that some doctors may split trimesters into 12 weeks each, while others may add an extra week. Follow your doctor's calculation for the duration of your pregnancy, and don't hesitate to check with her if you have any doubts at all.
Is pregnancy nine or 10 months long?
It depends on how you count it. Most people determine their due date by counting 40 weeks from the first day of their LMP.
40 weeks adds up to about:
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- nine calendar months (30 or 31 days each) or
- 10 lunar months (28 days each)
Keep in mind that you're not actually pregnant for the first two weeks because you haven't even ovulated yet, and you don't usually find out you're pregnant until you're about 5 weeks or so along. But this is how most people count it.
In order to make it easy to count the months, a lot of guidebooks and websites, including BabyCenter India, will count the months of pregnancy as lunar months.
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So, every four weeks, you're another "month" along. Counting this way, you will be 10 lunar months pregnant by the time 40 weeks is up!
Isn't a month four weeks long?
Actually, the only month that's four weeks (or 28 days) long is February - that is, when it's not a leap year. All the others are either 30 or 31 days. So, on average, a month is 30.4 days long - or 4.3 weeks.
How will I know how many weeks pregnant I am?
There's no way to know for sure exactly when you ovulated and conceived. As a result, most people, including health professionals, will date your pregnancy based on your LMP (last menstrual period) instead.
To work out how many weeks pregnant you are by this measure, try to remember when your last period started. The first day of your LMP counts as day one of your pregnancy. You can find out your estimated due date using our handy due date calculator.
Some women prefer to count their pregnancy from the day they were likely to ovulate during the month they became pregnant.
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This will give you an estimated date of conception, which will usually be about two weeks after the first day of your LMP. So you will be two weeks further along in your pregnancy if it's calculated according to your LMP rather than your estimated date of conception.
So, that's why BabyCenter, and most health professionals, say that you've been pregnant for about two weeks longer than you really have been.
How do I convert weeks of pregnancy into months?
Find how many weeks pregnant you are on the chart and scan back to see approximately how many months pregnant you are.
(Note that you're not one month pregnant until it's been one month since your LMP.)
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Download this chart showing the weeks, months, and trimesters of pregnancyOpens a new window.
I'm confused by what week it is in my pregnancy. How can I be sure?
To understand this, it may help to think about age. When a baby is one year old, he has finished his first year of being alive. This means that he will be one year old during his second year of life.
Similarly, you are one week pregnant when you complete your first week of pregnancy. So, you will be one week pregnant during your second week.
It's all about completing each week - putting one week behind you and starting another one. Therefore:
- in your first week, you are zero weeks pregnant
- in your second week, you are one week pregnant
- in your third week, you are two weeks pregnant
- in your fourth week, you are three weeks pregnant
- in your fifth week, you are four weeks pregnant
This is why your personalised weekly newsletters from BabyCenter India will tell you that you're four weeks pregnant when you're in your fifth week of pregnancy.
If you haven't already, sign up for BabyCenter's My Pregnancy this week newsletters here.
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Is my baby the size BabyCenter's fetal development pages say?
Each of our weekly fetal development pages has information about your unborn baby's size and weight. These are average figures.
All babies are about the same size early in pregnancy, but they begin to grow at different rates during the second trimester. That's why some full-term babies weigh less than 2.5kg, and some weigh more than 3.5kg.
Try not to worry too much if an ultrasound scan indicates your baby is not the average size. As your pregnancy progresses, the range of what's considered a normal size grows larger.
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Your doctor will let you know if she has any concerns about the size of your baby.
I'm getting the wrong week's newsletter. How do I change my date?
If you're just getting the newsletter for the wrong week, or if you've had your baby recently and still receiving pregnancy newsletters from BabyCenter India, or if all you need to do is update your family details.
- Either use the link above or click on your profile picture in the top right corner of the screen, then select ‘My profile’ and click on edit my family details.
- This will take you to the family details page.
- You can then remove or change your due date or birth date information.
- When you've changed your due date or your baby's birth date, click on "Save changes".
Now that you know how to date your pregnancy, check out our guide to pregnancy week-by-week.
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हिंदी में पढ़ें: गर्भावस्था गणना - हफ्तों, महीनों और तिमाहियों में
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