From conception to labor, your baby is constantly growing and developing. Your baby moves through different stages, starting as a blastocyst, then maturing into an embryo, and then a fetus. Around the 5 week mark, your baby’s heart will begin to beat, at 27 weeks they’ll have regular sleep and wake cycles, and at 39 weeks your baby is physically developed. Use this timeline to learn how big your baby is, plus how they’re developing throughout pregnancy.

First Trimester

2 weeks pregnant: It’s a potentially life-changing week. You’ll ovulate, and if egg meets sperm, you’ll be on your way to pregnancy!

3 weeks pregnant: Your baby is a tiny ball – called a blastocyst – made up of several hundred cells that are multiplying quickly.

4 weeks pregnant: Deep in your uterus, your baby is an embryo made up of two layers, and your primitive placenta is developing.

5 weeks pregnant: Your tiny embryo is growing like crazy, and you may be noticing pregnancy discomforts like sore breasts and fatigue.

6 weeks pregnant: Your baby’s nose, mouth, and ears are beginning to take shape. You may be having morning sickness and spotting.

7 weeks pregnant: Your baby – still an embryo with a small tail – is forming hands and feet. Your uterus has doubled in size.

8 weeks pregnant: Your baby is constantly moving, though you can’t feel it. Meanwhile, you may be making decisions about prenatal tests.

9 weeks pregnant: Nearly an inch long now, your baby is starting to look more human. You’ve probably noticed your waist thickening.

10 weeks pregnant: Your baby has finished the most critical part of development! Organs and structures are in place and ready to grow.

13 weeks pregnant: It’s the last week of the first trimester! Your baby now has exquisite fingerprints and is almost 3 inches long.

Second Trimester

14 weeks pregnant: Your baby’s tiny features are making different expressions. And you may be feeling more energetic and less nauseated.

15 weeks pregnant: Your baby can sense light and is forming taste buds. Have a stuffy nose? It’s a surprising pregnancy side effect. 

16 weeks pregnant: Get ready for a growth spurt. In the next few weeks, your baby will double his weight and add inches to his length.

17 weeks pregnant: Your baby’s skeleton is changing from soft cartilage to bone, and the umbilical cord is growing stronger and thicker. 

18 weeks pregnant: Your baby’s genitals are developed enough to see on an ultrasound. Hungry? An increase in appetite is normal now.

19 weeks pregnant: Go ahead and sing: Your baby may be able to hear you! And if your sides are aching, it could be round ligament pain.

20 weeks pregnant: Congratulations, you’re at the halfway mark in your pregnancy! Your baby is swallowing more now and producing meconium. 

21 weeks pregnant: Feeling your baby move? Those early flutters will turn into full-fledged kicks. Cool fact: She has eyebrows now!

22 weeks pregnant: Your baby is starting to look like a miniature newborn. And your growing belly may be turning into a hand-magnet.

23 weeks pregnant: When you’re on the move, your baby can feel the motion. Pretty soon, you may notice swelling in your ankles and feet.

24 weeks pregnant: Your baby is long and lean, like an ear of corn. And your growing uterus is now the size of a soccer ball.

25 weeks pregnant: Your little one is starting to add some baby fat and grow more hair. Your hair may be looking extra lustrous, too.

26 weeks pregnant: Your baby is inhaling and exhaling small amounts of amniotic fluid, which is good practice for breathing.

27 weeks pregnant: Feel a tickle? It may be your baby hiccupping. He’s also opening and closing his eyes and even sucking his fingers.

Third Trimester

28 weeks pregnant: Welcome to your last trimester! Your developing baby’s eyes may be able to see light filtering in through your womb.

29 weeks pregnant: Your baby’s muscles and lungs are continuing to mature, and her head is growing to make room for her developing brain.

30 weeks pregnant: Your baby now weighs almost 3 pounds. Meanwhile, you may be battling mood swings, clumsiness, and fatigue.

31 weeks pregnant: Your baby’s strong kicks might be keeping you up at night – and you may be feeling Braxton Hicks contractions, too.

32 weeks pregnant: Your baby is plumping up! Meanwhile, your expanding uterus may cause heartburn and shortness of breath.

33 weeks pregnant: With your baby now weighing a little over 4 pounds, you might be waddling – and having trouble getting comfy in bed.

34 weeks pregnant: Your baby’s central nervous system and lungs are maturing, and dizziness and fatigue may be slowing you down.

35 weeks pregnant: Your baby is too snug in your womb to do somersaults, but you’ll still feel frequent – if less dramatic – movements.

36 weeks pregnant: Your baby is gaining about an ounce a day. You may feel her “drop” down into your pelvis as you approach your due date.

37 weeks pregnant: Your baby’s brain and lungs are continuing to mature. You may have more vaginal discharge and occasional contractions.

38 weeks pregnant: Your baby has a firm grasp, which you’ll soon be able to test in person! Meanwhile, watch out for signs of preeclampsia.

39 weeks pregnant: Your baby is full term this week and waiting to greet the world! If your water breaks, call your healthcare provider.

40 weeks pregnant: Your baby is the size of a small pumpkin! Don’t worry if you’re still pregnant – it’s common to go past your due date.

41 weeks pregnant: As cozy as he is, your baby can’t stay inside you much longer. You’ll go into labor or be induced soon