Pregnancy Weeks and Trimesters

Your Pregnancy: Week by Week

Nine months can seem like forever when you're expecting a baby. But when you think about all that happens week by week during pregnancy, it's a wonder that so much gets done in that time frame.

You can see and feel some of the developments—your growing belly, your baby kicking. It's what you can't detect on your own, however, that is what's truly amazing, methodical, and complex.

Many don't realize this, but you start the first trimester when you are not even pregnant.

You might even be halfway through this trimester before you realize that you are expecting. Despite this, it is a busy time for your body and your baby—and as the weeks roll on, things only get busier.

Our guides to each trimester of pregnancy, week by week, give you a sense and a look at what's happening in these important periods.

Take a look at fetal development throughout pregnancy.

The First Trimester

Week 1 & Week 2
Though considered the first two weeks of your pregnancy, you are not actually pregnant.

However, your body is preparing. You’re having your last period for a long while in the first week. The second week, you are preparing to ovulate the egg that will be fertilized and building the uterine lining where that egg will eventually implant itself.

Week 3
You ovulation this week. The sperm will meet the egg in the outer part of the fallopian tube and begin its journey toward the uterus.

Week 4
The egg now implants itself in the uterus. You will also finally have some signals from your body that you are expecting. This is the earliest a pregnancy test would accurately show that you’re pregnant.

Week 5
This week your baby’s rudimentary heart will begin to beat. You might even start feeling some of the earliest symptoms of pregnancy from morning sickness to extreme exhaustion.

Week 6
While your baby's heart began beating last week, most early ultrasounds can only now pick up the tiny flickering pixels that indicate that heartbeat. It’s still too early to use external Doppler devices. If you haven’t had symptoms of pregnancy yet, this might be your lucky week.

Week 7
Your baby has a genital tubercle—the beginning of what will be the penis or clitoris. Your baby is also forming nostrils this week.

Week 8
This is the week of elbows and knees. The arm and leg buds have formed, and now come the parts that help them kick and wave. You may start your prenatal care this week.

Week 9
This week your baby weighs the same as a paper clip. It’s hard to imagine something so small has so many body parts (and that most of them are working to some degree). You might be feeling like you have a stuffy nose.

This is a common, but not fun, part of pregnancy.

Week 10
You might feel like you’re boasting a belly, though that bulge is not really the baby. That said, welcome to the fetal period.

Week 11
About half the baby is head at this period. Before you blame your partner, that’s perfectly normal. (Your baby's proportions will even out over time.)

Week 12
Your baby is moving around, though you don’t feel it. He or she is also producing bile.

Week 13
Your baby weighs a whole ounce at this point. That’s a huge leap in the last few weeks. Your baby also has formed teeth, but can’t bite yet.

The Second Trimester

Week 14
Your breasts have probably begun changing already. They may have previously been sore from preparing for breastfeeding, and you may also notice the darkening of the areola. This is normal.

Week 15
Your baby might be a thumb- or finger-sucker already. This is great practice for your baby. Your body has already increased its blood volume, which causes your heart to work harder.

Week 16
Your baby is emptying his or her bladder every 45 minutes.

You, on the other hand, can probably hold it a bit longer than that in this trimester. Some mothers will be able to feel the first flutterings of baby beginning this week, particularly if this is not your first baby or if you are really thin.

Week 17
Extra sweating is normal at this stage. You are carrying your own heat source (your baby), after all. Trying to stay cool can help, as can bathing and deodorant.

Week 18
Your baby weighs about seven ounces. It also happens that his or her bones are beginning to harden, a process known as ossification.

Week 19
Your baby is pretty hairy this week. He or she is covered with a fine hair called lanugo that will fall off closer to birth, and even a bit after.

Week 20
In addition to body hair, your baby’s skin is covered in a thick white coating called vernix. This helps protect the skin. If he or she is born at term, you won’t see much of it. Your uterus is at the point of your belly button or navel now. This means your doctor or midwife will start measuring it to see how your baby is growing.

Week 21
Your baby weighs just under a pound at this point. He or she can still move fairly freely in the amniotic fluid. You are most likely feeling your little gymnast now.

Week 22
Your baby now has eyebrows. If you haven’t yet, sign up for childbirth classes. They fill faster than you would imagine.

Week 23
You might notice that your abdomen is sometimes hard. This due to Braxton Hicks contractions, which are essentially practice contractions.

Week 24
Your baby is depositing something called brown fat. This will help him or her regulate body temperature after birth. This is also considered the week of viability, though your goal—of course—is to keep baby in as long as you can.

Week 25
Your partner might start to be able to feel the baby move. This is a huge deal for all involved. You are finishing up the second trimester soon.

Week 26
Are you having trouble sleeping? Various positions can help you get better rest. Experiment with what works well for you. Pillows are usually a must.

Week 27
Your baby weighs in at about two pounds. Though baby’s skin is wrinkled from floating in amniotic fluid, it will fill out after birth.

The Third Trimester

Week 28
Your baby now has some eyelashes. They will continue to grow and be normal length at birth. It’s worth noting that you will probably start seeing your doctor or midwife every other week now.

Week 29
The third trimester might make you feel not so great. There is a long list of aches and pains, but did you know that safe exercise and good posture can really alter how well you feel?

Week 30
Your baby can sense light and dark, which is pretty amazing considering the cozy "cave" he or she is resting in. Your baby can also hear your voice.

Week 31
Three pounds and a few ounces—that’s about the average weight for a baby at this point. That’s an amazing transition from the weight of a paper clip.

Week 32
Have you started thinking about the baby? That is, the one who will be in your home soon? Think about car seats and baby carriers, as well as other gear you may need. If you haven’t had a baby shower and plan to (or think one may be coming as a surprise), you may want to register soon.

Week 33
How prepared for labor are you? Have you read some books on labor and birth? Taken a childbirth class? Hired a doula? Time is going to start really passing quickly, so you may want to get educated about what's coming so you feel ready (or as ready as you can be).

Week 34
You may have some questions about where you'll give birth and what will happen when you're there, and a tour of your hospital or birth center can help address them. It’s also a great time to pre-register, if you haven’t already.

Week 35
Your baby’s brain is about to get really groovy (literally). It will grow a lot over the next few weeks until the very end of pregnancy.

Week 36
At about this point, you are entering what's roughly the last month of pregnancy. You will start seeing your doctor or midwife every week until you have the baby.

Week 37
You should pack a bag for labor and birth, if you haven’t already. Pack one for labor and one for postpartum. Be sure that your partner packs his or her own bag—and that it includes snacks!

Week 38
Some babies will be born beginning now, while others will hang out for awhile. Be sure you know who to call and how to determine when "it's time."

Week 39
This really isn’t a magic number, though some think it might be. Most babies are still snug in place, but you might be experiencing more pre-labor symptoms as you get closer.

Week 40
Congratulations on making it to your due date! How do you intend to celebrate? We suggest something enjoyable and relaxing—a nice date night with your partner, a massage, a pedicure. Remember, it may be a matter of hours or days (even weeks) before the big day, so take a moment for yourself.

Week 41
Sometimes babies stick in a bit longer and need some extra time. Try to be patient. You may see your doctor or midwife an extra time or two this week just to keep an eye on you and baby.

Week 42
If you are still pregnant, you are amazing...and probably miserable. Hang in there—most practitioners will recommend an induction of labor by the end of this week.

Variations in Pregnancies

There are a lot of things that you may find surprising about pregnancy. Some women seem to feel pregnant before the test turns positive, while others don't seem to feel anything until the baby starts to move. These are all variations of normal and not something to be concerned with in general.

Prenatal Care

You will get to know your practitioner(s) through prenatal care. This starts off feeling fairly slow-going, as you'll only have appointments about once a month until the third trimester. Appointments will increase to biweekly, then weekly come month nine, totaling about 13 or so when all is said and done. That may sound like a lot of time being evaluated, but many moms say they spend more time in the waiting room than with their OB.

Note that many practices encourage you to see all physicians in their practice over the course of your pregnancy (as any one of them may be the one delivery your baby, schedules depending). This has its benefits, though some women say it causes them to have to re-explain themselves each appointment. This may also make it very hard to really know the person who comes in during your birth. If this is a problem for you, you may want to consider switching practices.

Questions in Pregnancy

You will undoubtedly have a lot of questions over the weeks of your pregnancy. Write everything down. This includes specific questions that you have before a practitioner visit, as well as general topics you want to be sure you talk about while you're there. It's helpful to take notes during your appointments, too, or to have someone attend your visits with you so you can turn over this role.

Any time you have a question or are unsure of something, and you don't have an in-person appointment coming up in the immediate future, contact your midwife or doctor. You might be worried about seeming annoying, but don't be. These professionals know that pregnant women have a lot of questions and that they have the answers.

That said, non-emergent questions should be saved for daytime, regular office hours (not middle-of-the-night calls). Your practitioners, or even your insurance company, may even have a special hotline dedicated to answering questions you may have during your pregnancy; this is usually staffed by nurses.

A Word From Verywell

Remember that your pregnancy is likely to be at least slightly different than anyone you've known. There will be slight differences in everyone's growth and fetal development.

Though there is a lot going on during the weeks of pregnancy, remember that many moms look back and say that this time goes fast. Enjoy your pregnancy as much as you can.


March of Dimes Late Preterm Brain Development Card. March of Dimes. 2011.

Obstetrics: Normal and Problem Pregnancies. Gabbe, S, Niebyl, J, Simpson, JL. Sixth Edition.

Why the Last Weeks of Pregnancy Count. March of Dimes. 2010.

Your Pregnancy and Childbirth: Month to Month, Revised Sixth Edition. American College of Obstetricians and Gynecologists. 2016.

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