How Big Is Your Baby This Week? Week-by-Week Pregnancy Milestones
Track your baby's amazing week-by-week growth with relatable size comparisons and developmental milestones.
How Big Is Your Baby This Week?
Pregnancy is a journey filled with excitement, anticipation, and countless questions. One of the most common questions expectant parents ask is: “How big is my baby right now?” Tracking your baby’s growth week by week not only satisfies curiosity but also helps you understand the remarkable changes taking place inside your body. Each week brings a new stage of development, with your baby rapidly growing in size and complexity. In this comprehensive guide, we’ll explore your baby’s size and development during each week of pregnancy, using fun, relatable size comparisons and outlining the key milestones you and your baby will reach together.
First Trimester: Weeks 4 – 13
During the first trimester, your baby grows from a single cell to a complex embryo with developing organs, heartbeat, and early human features. Here’s how big your baby is each week, and the amazing changes happening inside:
Weeks 4–5: Poppy Seed – Sesame Seed
- Size: About the size of a poppy seed at 4 weeks, growing to a sesame seed by 5 weeks.
- Milestones: Fertilized egg implants in the uterus, forming the embryo and placenta. Basic structures for the brain, spinal cord, and heart begin to develop.
Week 6: Lentil
- Size: About the size of a lentil.
- Milestones: Baby’s neural tube (which becomes the brain and spinal cord) closes. The heart starts beating and blood begins to circulate.
Week 7: Blueberry
- Size: Roughly the size of a blueberry.
- Milestones: Bones start to form, though still soft. Eyelids develop and stay shut. Genitals begin to form.
Week 8: Kidney Bean
- Size: Size of a kidney bean.
- Milestones: Major organs and body systems are developing. The placenta is now functioning, providing crucial nutrients.
Week 9: Grape
- Size: About the size of a grape, close to ½ an inch long.
- Milestones: Tiny buds appear for future teeth. Facial features such as the tip of the nose and eyelids become more distinct.
Week 10: Prune
- Size: Size of a prune.
- Milestones: Fingers and toes continue developing. Nails begin to grow. You might hear your baby’s heartbeat at a prenatal checkup.
Week 11: Lime
- Size: Roughly the size of a lime.
- Milestones: Bones start to harden. The skin remains thin and transparent, but will soon become less so. The head is nearly half the baby’s size.
Week 12: Plum
- Size: About the size of a plum, 2 inches long and ½ an ounce.
- Milestones: Hands are developing faster than feet. Movements increase, though you likely won’t feel them yet.
Week 13: Peach
- Size: Size of a peach.
- Milestones: The second trimester begins. Organs are fully formed and continue to mature. Ultrasounds may show breathing and swallowing motions.
Second Trimester: Weeks 14 – 27
The second trimester is a period of rapid growth. By the end, your baby will be much larger and capable of more complex movements and responses.
Week 14: Lemon
- Size: Size of a lemon.
- Milestones: Eyes begin to move. Nose and taste buds are developing. Skin thickens, and hair follicles form. Baby starts to open and close hands and brings them to the mouth.
Week 15: Apple
- Size: Size of an apple.
- Milestones: Skeleton begins to harden, and baby may be able to make facial expressions. The scalp hair pattern is forming.
Week 16: Avocado
- Size: Size of an avocado.
- Milestones: Limbs are more flexible, and movements are becoming coordinated. Ears are close to their final position on the head.
Week 17: Turnip
- Size: About the size of a turnip.
- Milestones: Sweat glands are developing. The skeleton continues to harden, turning from cartilage to bone.
Week 18: Bell Pepper
- Size: Bell pepper sized.
- Milestones: Ears stand out on the sides of the head and can detect sounds.
Week 19: Heirloom Tomato
- Size: Heirloom tomato.
- Milestones: Kicks and movements grow stronger; baby learns to suck (necessary for feeding after birth) and might even suck their thumb.
Week 20: Banana
- Size: About 10 inches long, weighing 1 pound—comparable to a banana.
- Milestones: Nails are growing to the ends of fingers. First-time mothers may start feeling baby’s movements.
Week 21: Carrot
- Size: Carrot length.
- Milestones: Fingers and toes are fully formed, including fingerprints and toe prints. Baby is able to swallow and may hiccup, felt as jerky movements.
Week 22: Spaghetti Squash
- Size: Spaghetti squash.
- Milestones: Eyelids remain closed but eyes move behind them. Tear ducts develop. Eyebrows may start to appear. Baby may move suddenly in response to loud sounds.
Week 23: Grapefruit
- Size: Grapefruit sized.
- Milestones: Baby can recognize sounds, such as your voice. Talking to your baby may prompt movement in response.
Week 24: Ear of Corn
- Size: About 12 inches long and weighing a little more than 1 pound—like an ear of corn.
- Milestones: Rapid muscle growth. Some hair may be present on the head. Lungs are fully formed but not yet mature enough for breathing outside the womb.
Week 25-27: Rutabaga to Cauliflower
- Size: From rutabaga to cauliflower.
- Milestones: Baby experiences growth in both size and complexity. Nervous system matures, and movements continue to get stronger.
Third Trimester: Weeks 28 – 40
The third trimester is the home stretch. Your baby is growing rapidly—gaining weight, practicing breathing, and preparing for life outside the womb.
Week 28: Eggplant
- Size: Similar in size to an eggplant.
- Milestones: Eyes can open and close, and baby can sense changes in light. Layers of fat are forming, and the brain continues to develop quickly.
Week 29-30: Butternut Squash to Cabbage
- Size: As large as a butternut squash, progressing to a cabbage.
- Milestones: Baby’s bones are fully developed, though still soft. Brain and lungs continue to mature. Baby is practicing breathing by inhaling and exhaling amniotic fluid.
Week 31: Coconut
- Size: Coconut sized.
- Milestones: The brain grows rapidly and now helps regulate body temperature. Movements may feel more coordinated and rhythmic.
Week 32: Jicama
- Size: About 18 inches long, weighing close to 5 pounds—similar to a jicama.
- Milestones: Skin is now opaque, thanks to added fat. The immune system is getting stronger and preparing to function independently after birth.
Week 33: Pineapple
- Size: Pineapple.
- Milestones: Baby is gaining about half a pound per week, getting plumper as the due date approaches.
Week 34: Cantaloupe
- Size: Cantaloupe.
- Milestones: Vernix (the creamy layer protecting baby’s skin) gets thicker. Most babies move into a head-down position, readying for delivery.
Week 35: Honeydew Melon
- Size: Honeydew melon.
- Milestones: Brain and lungs keep developing. A baby’s brain at 35 weeks is only two-thirds of what it will be by full-term. If pregnancy is healthy, it’s best to let labor begin on its own unless medically necessary.
Week 36: Head of Romaine Lettuce
- Size: Head of lettuce, weighing about 6 to 7 pounds.
- Milestones: Movements may feel less dramatic due to crowded conditions, but you’ll still sense kicks and stretches. Changes in movement frequency should always be reported to your healthcare provider.
Week 37–40: Small Pumpkin to Watermelon
- Size: Your baby grows from the size of a small pumpkin (around 18-20 inches and 6-9 pounds) to a watermelon by week 40.
- Milestones: Baby reaches full maturity. Lungs and brain are fully developed, and baby is ready for birth. Most babies are born head-down, but positions may vary. At this stage, you may feel a lot of pressure as the baby descends deeper into your pelvis in preparation for delivery.
Comparing Baby Size Week by Week
| Week | Baby Size | Developmental Milestones |
|---|---|---|
| 4 | Poppy Seed | Implantation, embryo forms |
| 8 | Kidney Bean | Organ and body system development |
| 12 | Plum | Movement increases |
| 20 | Banana | Nails grow to fingertips, weight ~1 lb |
| 24 | Ear of Corn | Lungs fully formed, rapid muscle growth |
| 32 | Jicama (~5 lbs) | Skin opaque, immune system matures |
| 36 | Romaine Lettuce (6–7 lbs) | Less room to move, notice movement frequency |
| 40 | Watermelon (6–9 lbs) | Full maturity, ready for birth |
Pregnancy Milestones: What Else Is Happening Each Week?
- Organ Development: Most organs form in the first trimester and continue to mature throughout pregnancy.
- Heartbeat: Typically detectable around week 10.
- Movement: Early movements occur by week 8; stronger kicks by week 19-20.
- Senses: Baby learns to recognize your voice and responds to sounds by week 23.
- Brain Growth: Accelerates in the final weeks, helping your baby regulate body temperature and breathing.
- Preparation for Birth: Baby gains weight, stores fat, and acquires protective vernix for the outside world in the last month.
Frequently Asked Questions (FAQs)
Q: How accurate are baby size comparisons each week?
A: Baby size comparisons, such as fruits and vegetables, are useful visual guides based on average fetal length and weight. Keep in mind, every pregnancy is unique and actual sizes may vary.
Q: When can I start feeling my baby move?
A: Many first-time mothers begin feeling fetal movement, often called quickening, between weeks 18 and 22. If you’ve had a previous pregnancy, you may notice movement earlier.
Q: What if my baby seems smaller or larger than the weekly average?
A: Ultrasound measurements and medical assessments help estimate your baby’s size. Variations are common and your healthcare provider will monitor growth to ensure everything is on track.
Q: Why does my baby’s position change in late pregnancy?
A: Most babies switch to a head-down position by week 34, which is optimal for birth. Some may not shift until later, but healthcare providers monitor this closely in the final weeks.
Q: Are changes in movement a cause for concern?
A: If you notice a decrease in your baby’s usual movements, especially after week 28, contact your healthcare provider promptly to ensure your baby’s well-being.
Tips for Tracking Your Baby’s Growth
- Attend all prenatal appointments for close monitoring of your baby’s health and size.
- Keep a pregnancy journal or use a pregnancy app to note weekly changes and experiences.
- Eat a balanced diet and stay hydrated to support baby’s growth and development.
- Don’t hesitate to ask your healthcare provider about any concerns regarding your baby’s size or development.
Conclusion
Pregnancy showcases the intricate process of human development, week by week. Watching your baby grow from a tiny cluster of cells to a fully formed infant is awe-inspiring. Use this guide to follow your baby’s size and major milestones, nurture your own health, and cherish the transition into parenthood. Every journey is different, so remember that your baby’s growth will follow their unique timeline—enjoy each new week and milestone!
