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Pregnancy trimester timeline – week-by-week guide

Mother holds newborn

First trimester

Your bump: Week 1

It’s week one of your pregnancy, but you’re not actually pregnant! That’s right - your doctor tracks your pregnancy and due date from the first day of your last period. So, what’s going on? Your body is preparing for the moment you do get pregnant – your uterus is thickening and getting ready for the arrival of your fertilized egg. You may even notice an increase in cervical mucus as you head towards conception. Make sure you start getting at least 400 micrograms of folic acid daily – a must for baby’s brain and spinal cord development!

Your bump: Week 2

It’s week two and you’re ovulating. If sperm meets an egg in your fallopian tube, you’re going to conceive! During this time, you may notice some light spotting. This isn’t your period - it’s a sign that a fertilized egg has attached itself to the wall of your uterus!

Your bump: Week 3

Congratulations, mama - you’re pregnant (but you don’t feel it yet)! Sperm and egg have merged to form a single cell called a zygote – and a lot is going on inside that tiny cell! Your and your partner’s chromosomes are combining to decide baby’s gender, hair and eye color. As the zygote starts traveling from the fallopian tubes to your uterus, it’s dividing into multiple cells which will go on to become each organ in your baby’s body. Pretty cool, huh?

Your bump: Week 4

The real work has begun! Your embryo has attached to the wall of your uterus and is about the size of a poppy seed. Cells continue to divide to create your baby’s organs and your amniotic sac is forming which surrounds and protects your baby as he or she grows. Also attached to the amniotic sac is the yolk sac, which will feed your baby during these early weeks. You’ll miss your period but may notice some spotting – this is called implantation bleeding and it’s normal. If you’ve taken a test and it’s negative, no worries – it can take a week or more after a missed period for pregnancy hormones (hCG) to be detected on a test. 

Your bump: Week 5

Your pregnancy hormones are high enough to show a positive pregnancy test! Your little embryo may resemble a tadpole, but not for long! Right now, your embryo is starting to look like a fetus with a neural tube (formation of spinal cord and brain) running from head to bum. Another tube is developing your baby’s heart, while tiny buds will grow into arms and legs. During week 5, you might start to feel early pregnancy signs – exhaustion, tender breasts and bouts of nausea. 

Once you have that positive pregnancy test, it’s time to schedule your first prenatal appointment. Find an OBGYN or midwife that’s right for you.

Your bump: Week 6

Your baby is the size of a sweet pea. You may not be able to hear it, but your baby’s little heart has started to beat! He or she still looks like a tiny tadpole, but their face is starting to take shape. Your body hasn’t changed much, but you may have noticed an increasing urge to urinate, breast tenderness, nausea and bloating. Now is the time to start preparing for your first prenatal visit – be prepared for lots of tests and questions!

Your bump: Week 7

Your baby is the size of a blueberry and is already developing every organ he or she will need! Baby’s heart, kidneys, liver, lungs, intestines and arms and feet are forming. Your baby is now attached to you by an umbilical cord, so you can provide food and filter away any waste. You may be coping with nausea, food cravings and aversions and very swollen, tender breasts. Now’s a good time to invest in a good maternity bra!

Your bump: Week 8

Your baby is the size of a raspberry and his or her hands and feet are sprouting webbed fingers and toes! You may not look pregnant, but you’re probably feeling it. Inside your uterus, your baby is growing fast – in fact, he or she has officially graduated from embryo to fetus. Your baby now has lips, a nose and very thin eyelids! You might be thinking about first-trimester prenatal tests – your OBGYN or midwife can help you decide what’s right for you.

Your bump: Week 9

Your baby is now the size of a cherry, and he or she is looking more like a tiny human – that tadpole-like tail is almost gone! Your baby’s reproductive organs are forming, but it’s still too early to know if you’re having a boy or girl. You’re probably feeling extreme pregnancy fatigue – hang in there, mama! Your energy levels will increase once you’re into your second trimester. Try to catch some extra sleep and snooze on your left side. This allows for better blood flow to baby.

Your bump: Week 10

Your baby is the size of a strawberry, and his or her tiny fingernails are starting to develop. You may not be able to feel it yet, but your baby is kicking up a storm – and flexing his or her tiny arms. At your next prenatal appointment, you may even be able to hear your baby’s heartbeat! Feeling a little backed up? Constipation is a common first-trimester symptom. Try adding more fiber to your diet – and don’t forget to wash it down with plenty of water!

Your bump: Week 11

Your baby is now the size of a lime and is busy growing and moving – but you won’t feel these movements for another month or two. At week 11, your baby has distinct human characteristics – hands and feet, ears and even nasal passages on his or her tiny nose. You may be noticing some changes, too. Extra gassy and bloated? Thank the pregnancy hormone progesterone. Try to opt for smaller meals – don’t forget that fiber!

Your bump: Week 12

Your baby is the size of a plum and can open and close hands and curl his or her tiny toes! You’re probably barely showing, but your baby has more than doubled in size during the last three weeks. Most of your baby’s systems are fully formed, but there’s a lot of maturing to do! Your early pregnancy symptoms are starting to subside, but you may start to feel dizzy (thanks again, progesterone). If you feel dizzy, sit or lie down, breathe deeply and loosen any tight clothing. Once you feel better, grab something to eat and drink.

Your bump: Week 13

Congratulations, mama - you made it through your first trimester! Your baby is now the size of a lemon, and his or her body is starting to look more proportional. Fingerprints are starting to form on your baby’s tiny fingertips and if you’re having a girl, her ovaries are filled with more than two million eggs! Also developing this week, your baby’s vocal cords. Your second trimester should bring some sweet relief from your early pregnancy symptoms. However, you may have noticed an increase in vaginal discharge called leukorrhea. If it makes you more comfortable, wear a panty liner to stay dry.

Second trimester

Your bump: Week 14

Your baby is as big as a peach or Rubik’s cube, about 3.42 inches long. At this point, he or she can suck their thumb! Your little one’s face has all its features, and they are starting to respond to outside noises and movement. You may also notice some constipation around this time. Moderate exercise, plenty of fluids, fruits and vegetables can help to ease constipation.

Your bump: Week 15

Your baby is the size of an apple or a baseball, about 3.98 inches. They are forming taste buds and their skeleton is ossifying—officially turning into bone. To help with your circulation, you’ll want to begin sleeping on your left side with the assistance of a pillow, if needed. At this point, you may wish to undergo prenatal tests that can screen your child for disorders such as Down syndrome.

Your bump: Week 16

Your child is now the size of an avocado or a light bulb at 4.57 inches! You can now hear your baby’s heartbeat at your doctor visits. Your body’s blood volume has increased to help support your baby, and you may notice your leg veins are more prominent. Ask your doctor about wearing support stockings and light exercise to help improve your blood flow.

Your bump: Week 17

Your baby is the size of a pear or softball at around 5.12 inches. You might start to feel baby hiccup now, and he or she has doubled in weight over the last two weeks. Your appetite has grown and your baby now has some fat to help with heat protection and their metabolism. During this time, you might start to feel dizzy or faint. Move slowly to help with this, especially when moving from lying down.

Your bump: Week 18

Your baby is about the size of a sweet potato, measuring around 5.59 inches. At this point, you may be able to learn the sex of your child! You’ll have a mid-pregnancy ultrasound between now and week 22 to check on baby’s development and verify a due date. At this point, your heart is working up to 50% harder to support your pregnancy. How amazing is that?

Your bump: Week 19

Your little one is about the size of a mango, measuring around 6.02 inches. Your baby is starting to move around, and you can really feel it now! If you don’t, that’s OK—women feel this at different times during their pregnancy. These movements are tiny, and they may feel like flutters or even gas. They’ll continue to grow stronger throughout the second trimester.

Your bump: Week 20

At half way through your pregnancy, your baby is now the size of a banana - 10.08 inches. Noticed a big jump in that measurement? Your baby is now measured from head to toe, rather than from crown to rump. Now is a great time to sign up for childbirth classes. Also, watch your posture to help ease any back pain you’re feeling.

Your bump: Week 21

Your little one is about the size of a carrot at 10.51 inches. His or her eyelids are fully formed, and their growth rate starts to slow down now. Baby has even started to form buds for permanent teeth. You’re probably really starting to show now, too!

Your bump: Week 22

Your baby is the size of a small spaghetti squash at 10.94 inches. With eyebrows and stronger muscles, your little one is moving a lot at this point. You may be feeling more cramps and swelling of your feet and ankles. Eat more calcium and potassium to help combat those cramps!

Your bump: Week 23

Your baby is the length of an eggplant, around 11.38 inches. The fine hair, called lanugo, that covers baby’s body may grow darker. Your skin may be itchy as it stretches to accommodate your growing baby. Using lotions will help to ease the itch—just be sure to ask your doctor about any creams you’re consider using!

Your bump: Week 24

Your baby is the length of an ear of corn, about 11.81 inches. Baby can “open” their nostrils to practice breathing, and his or her brain is beginning to develop quickly. You’ll start gaining about one pound a week after this point and will be tested for gestational diabetes (a pregnancy-related, high-blood-sugar condition) between now and week 28. If you test positive, no worries! It’s not permanent and your doctor will help you navigate the rest of your pregnancy.

Your bump: Week 25

Your baby is the size of a rutabaga, measuring around 13.62 inches. You might be able to feel him or her kicking your ribs (it’s an accident!), and they can stick their tongue out. Thanks to extra hormones, your hair will feel fuller, but you might be experiencing ingestion, heartburn or hemorrhoids. Whatever treatments you use, avoid laxatives and mineral oil. 

Your bump: Week 26

Your baby is now the length of a scallion, about 14.02 inches. The nerves in the ears are developing, so baby can respond to your voice and will even “dance” to music! They’re starting to breathe, exhaling amniotic fluid and getting their immune system ready by soaking up your antibodies. At this point, especially if you’re pregnant with twins, you might start experiencing Braxton Hicks contractions—but no worries. It’s just your body practicing for labor. Make sure to let your doctor know if they are severe or steady. 

Your bump: Week 27

Your baby is the size of a cauliflower, measuring 14.41 inches. He or she may be able to distinguish between your and your partner’s voices! They’re beginning to show brain activity at this point, too. You may start to notice stretch marks and balance problems. Be careful when exercising and talk with your doctor about any creams you want to use on your stretch marks. It’s also time to start thinking about a birth plan—how fun! 


Third trimester

Your bump: Week 28

Your baby’s as big as a medium squash, about 14.8 inches long! Baby’s brain is beginning to form grooves as it develops into a more complex organ – your little one may even begin to dream! Baby’s eyelids are opening now and lungs are forming bronchi, tiny tubular branches that carry air through the lungs. Mom, if you tested Rh negative, you’ll receive your injection this week to keep baby safe (if you haven’t already received it yet).

Your bump: Week 29

Your baby’s as big as a large butternut squash, about 15.2 inches long! Baby’s muscles are maturing, along with every other part of baby’s body, including brain and lungs. Baby’s also able to detect light from inside your belly! You may experience Braxton Hicks contractions. Don’t panic, mom – these are commonly called practice contractions and can last from 30 seconds to two minutes. However, if contractions become closer together or more painful, or if you being to leak fluid, call your care team or head to the nearest hospital to make sure you’re not going into labor early.

Your bump: Week 30

Your baby’s as big as a head of cabbage, about 15.71 inches long! Baby’s eyebrows and eyelashes are fully formed, and so are those tiny hands (with even tinier fingernails starting to grow). With less space inside your belly, baby is getting cozy and sleeping in 30- to 90- minute bursts. But that doesn’t mean mom is. Although you’re likely feeling extra sleepy these days, getting a good night’s rest may become more difficult. Try experimenting with different sleep positions or talk to your care team. Now is also a good time to sign up for childbirth education classes, if you haven’t already done so.

Your bump: Week 31

Your baby’s the size of a coconut, about 16.18 inches long! Baby’s getting pudgier, as an extra layer of fat begins to develop under the skin. Your little one can now make out distinct sounds, like voices and music. Mom, you may begin to notice stains on your shirt or that your breasts are leaking a creamy, yellowish substance called colostrum. This is the first stage of breast milk starting to develop.

Your bump: Week 32

Your baby’s as big as a Napa cabbage, about 16.69 inches long! Baby is beginning to breathe and lungs are continuing to mature but aren’t quite there yet. If you gave birth now, baby would need to be on a ventilator. Now is the time to choose a pediatrician for your newborn, if you haven’t already done so. Find a pediatrician near you.

Your bump: Week 33

Your baby’s as big as a large pineapple, about 17.2 inches long! The fine layer of body hair covering baby, called lanugo, is falling off, leaving hair only where it’s supposed to be – on baby’s head, eyebrows and eyelashes. Now is a good time to start thinking about what form of birth control, if any, you plan to use after your delivery – yes, it’s possible to get pregnant just a few weeks after your little one arrives!

Your bump: Week 34

Your baby’s the size of a cantaloupe, about 17.72 inches long! Baby’s bones are fully developed now, so don’t be surprised if you feel a few extra jabs and karate kicks inside your belly. Although you’ve still got several weeks to go before the big arrival, now is a great time to pack your hospital bag. 

Your bump: Week 35

Your baby’s the size of a honeydew melon, about 18.19 inches long! By now, baby’s likely made the downward turn and is facing head down, called vertex. Your little one’s still plumping up with fat deposits under the skin to prepare for womb departure. Your OBGYN or midwife may send you for a Group B strep (GBS) test, to check for GBS bacteria. If you test positive, don’t panic – we’ll simply ask you to come to the hospital as soon as labor begins to get you started on antibiotics that protect baby.

Your bump: Week 36

Your baby’s the size of a canary melon, about 18.66 inches long! Baby is plumping up with more fat developing. Skin is becoming smoother and less wrinkly, getting primed for plenty of snuggles. By now, baby’s lungs are fully mature. Mom, your back may ache more and you may feel heaviness in your lower body as baby drops lower into your abdomen. We’ll see you every week to monitor your progress and teach you about signs of labor and when its time to go to the hospital.

Your bump: Week 37

Your baby’s as long as a bunch of Swiss chard, about 19.13 inches long! You’re in the home stretch and space in your belly is getting tighter – which means baby has less room to kick. You’ll feel more wiggles and stretches. We’ll continue to see you each week and will monitor your blood pressure to watch for preeclampsia, a high blood pressure caused by pregnancy. 

Your bump: Week 38

Your baby’s as long as a stalk of rhubarb, about 19.61 inches long! Baby is still gaining weight (mainly fat to stay warm), but all organs should be fully functioning. Reflexes are working now too, and the brain is ready for life outside the womb. Your feet may swell more, which is a normal part of pregnancy. However, if you experience sudden or severe swelling in your hands, feet, ankles or face, call your care team, as this can be a sign of preeclampsia.

Your bump: Week 39

Your baby’s the size of a mini watermelon, about 19.96 inches long! You’re almost at the finish line, and baby’s grand entry could be any day now! Baby has dropped down into your pelvis, which may provide some relief. Your Braxton Hicks contractions may kick up a notch. Monitor your body, but don’t become obsessive. If contractions become more frequent and intense, it’s time to call your OBGYN or midwife.

Your bump: Week 40

Your baby’s as big as a watermelon, weighing between 6.5 to 8 lbs. and measuring about 20.16 inches long – full size! Although you’ll be meeting your bundle of joy any day now, babies like to set their own schedules. Try to rest and relax as best as you can. If you’re past your due date, talk to your care team about whether you’ll be induced for labor. Hang in there – you’re almost there!

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