From conception to labor, your baby is constantly growing and developing. Your unborn child goes through several developmental stages as it develops from a blastocyst to an embryo to a fetus. Your baby’s heart will start to beat around week 5, they’ll have normal sleep and wake cycles by week 27, and they’ll be physically mature by week 39. Use this timeline to learn how big your baby is, plus how they’re developing throughout pregnancy.

First Trimester

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: The nose, mouth, and ears of your unborn child are starting to form. You could be spotting and experiencing morning sickness.

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

8 and 9 weeks pregnant: Your baby is constantly moving, though you can’t feel it. Meanwhile, you may be making decisions about prenatal tests.

10 weeks pregnant: The most crucial stage of growth for your kid is over! Structures and organs are present and prepared to develop.

11 weeks pregnant: Soon, your baby’s hands will open and close into fists, and behind the gums, little tooth buds are starting to erupt.

12 weeks pregnant: Your little one’s teeny toes can curl, her brain is growing furiously, and her kidneys are starting to excrete urine.

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 and 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.

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

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 infant is almost 3 pounds now. You could be coping with mood swings, clumsiness, and exhaustion in the meanwhile.

31 and 32 weeks pregnant: Your baby’s strong kicks might be keeping you up at night. Your baby is plumping up!

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 and 38 weeks pregnant: Your baby’s brain and lungs are continuing to mature. 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: This week, your baby is at full term and eager to see the world. Call your healthcare practitioner if your water breaks.

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: Your kid can only stay inside you for so long, comfortable as he is. You will shortly go into labor or have an induction .