17 Weeks Pregnant: Baby's Skeleton Is Hardening

At 17 weeks pregnant, your baby is about the size of a pomegranate or turnip (approximately 130-140 mm or 5.1-5.5 inches). Your baby’s skeleton is transitioning from soft cartilage to hardening bone, and sweat glands are developing. You may start feeling movements more regularly now.¹

What’s Happening at 17 Weeks Pregnant?

Week 17 keeps you in the comfortable, energetic second trimester. Your baby is growing rapidly—both in length and weight—and becoming more active every day. If you haven’t felt movements yet, you likely will within the next few weeks.

Your body is visibly pregnant now, with a noticeable bump and the pregnancy “glow” that comes from increased blood flow. This is an excellent time to tackle projects, enjoy activities, and prepare for your baby’s arrival while you still have abundant energy.²

You’re also getting closer to the anatomy ultrasound (typically performed at weeks 18-20), which will provide a detailed look at your baby’s development and may reveal your baby’s sex if you choose to find out.

How Big is My Baby at 17 Weeks?

Your baby at 17 weeks is about the size of a pomegranate or turnip, measuring approximately 130-140 millimeters (5.1-5.5 inches) from crown to rump and weighing about 140-150 grams (4.9-5.3 ounces).³

Your baby’s weight is increasing rapidly now—gaining about 0.5 ounces (14 grams) per week on average.

Baby Development at Week 17

Significant structural and functional development continues:

Skeleton hardening: Your baby’s skeleton is transforming from soft, flexible cartilage into bone (ossification). This process requires significant amounts of calcium and will continue throughout pregnancy and childhood. The bones in the skull remain soft and somewhat separate to allow your baby’s head to compress during birth.⁴

Umbilical cord strengthening: The umbilical cord is becoming thicker and stronger to support increasing blood flow to your growing baby.

Sweat glands developing: Sweat glands are forming across your baby’s skin, though they won’t function until after birth.

Fat accumulation beginning: Your baby is starting to develop a thin layer of fat beneath the skin. This “baby fat” helps with temperature regulation and energy storage.

Increased movement: Your baby is very active, moving frequently throughout the day. These movements are becoming stronger and more coordinated:

• Kicking and punching
• Somersaults and rolls
• Grasping the umbilical cord
• Sucking thumb or fingers
• Hiccuping
• Practicing breathing movements⁵

Sensory development:

• Hearing: Your baby can hear sounds clearly now—your voice, your heartbeat, digestive sounds, music, and external noises
• Taste: Actively tasting amniotic fluid flavored by what you eat
• Touch: Sensitive to touch throughout the body

Circulatory system: Your baby’s heart is beating at 140-150 beats per minute and pumping increasingly large amounts of blood through the body.

Fingerprints: The unique patterns that form fingerprints are completely developed and will remain the same for life.

Immune system development: Your baby’s immune system is beginning to develop, though it won’t be fully functional until well after birth.

Brain development: The brain continues growing rapidly, with billions of nerve cells forming complex connections that control movement, senses, and eventually thought.

Respiratory practice: Your baby is practicing breathing movements, which help develop the lungs and respiratory muscles.

Common Symptoms at 17 Weeks Pregnant

Week 17 typically brings continued comfort with some new physical changes:⁶

More noticeable movements: If you’ve already felt movements, they’re likely becoming more frequent and distinct.

Increased appetite: Your baby is growing rapidly, and your body needs extra energy.

Growing bump: Your bump is becoming more pronounced and may be visible even in loose clothing.

Round ligament pain: Sharp, brief pains when changing positions or moving quickly.

Lower back pain: As your belly grows and your center of gravity shifts, back pain may increase.

Leg cramps: Some people experience painful leg cramps, especially at night.

Nasal congestion: Pregnancy rhinitis may continue.

Heartburn and indigestion: Ongoing as your uterus expands and pushes on your stomach.

Increased vaginal discharge: Normal and protective throughout pregnancy.

Skin changes: Possible darkening of skin in certain areas (linea nigra, melasma) or the pregnancy glow.

Increased blood volume: You now have about 40-50% more blood than before pregnancy, which can make you feel warmer and cause veins to be more visible.

Better sleep: Most people sleep reasonably well during the second trimester.

Weight gain: You’ve likely gained 5-15 pounds by now (weight gain varies significantly among individuals).

When to Call Your Doctor

Contact your healthcare provider if you experience:

• Heavy bleeding or passing clots
• Severe abdominal pain
• Fever above 100.4°F (38°C)
• Severe, persistent headache
• Sudden vision changes
• Sudden severe swelling

Tips for Week 17

Increase calcium intake: Your baby’s bones are hardening rapidly. Aim for 1,000-1,300 mg of calcium daily through dairy products, leafy greens, fortified foods, or supplements.

Address leg cramps: Stretch your calves before bed, stay hydrated, ensure adequate calcium and magnesium intake, and wear supportive shoes.

Support your back: Practice good posture, avoid prolonged standing, wear supportive shoes, use proper lifting technique, and consider prenatal yoga or swimming to strengthen back muscles.

Stay active: Continue regular, moderate exercise. Strengthening your core and back muscles can help prevent or reduce back pain.

Sleep comfortably: Sleep on your left side with pillows supporting your belly and between your knees. Consider a pregnancy pillow for added comfort.

Drink plenty of water: Aim for 8-10 glasses daily to support increased blood volume and prevent leg cramps.

Listen to music: Your baby can hear now, so playing music or singing may be enjoyable for both of you.

Schedule your anatomy ultrasound: Confirm your appointment for the detailed ultrasound at weeks 18-20.

Prepare to learn your baby’s sex: Decide whether you want to find out at the anatomy scan or wait until birth.

Start thinking about baby gear: Research cribs, car seats, strollers, and other essential items.

Consider maternity photos: The second trimester is an ideal time for maternity photos—your bump is visible but you’re still comfortable and energetic.

Tracking Your Pregnancy with Nooko

At 17 weeks pregnant, your baby’s skeleton is hardening and movements may be becoming more noticeable. Tracking these developments helps you appreciate your baby’s rapid growth and stay connected to your pregnancy journey.

With Nooko, you can log when movements become more regular and distinct—documenting the frequency and timing helps you notice patterns. Track your calcium intake to ensure you’re supporting bone development. Log symptoms like back pain or leg cramps to identify triggers and effective remedies.

Access detailed week-by-week information about your baby’s development. Take weekly bump photos to visualize your changing body. Set reminders for exercise, hydration, and prenatal appointments. Plan for upcoming milestones like the anatomy scan. Download Nooko to make your pregnancy journey well-documented and memorable.

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References

Footnotes

1. American College of Obstetricians and Gynecologists. (2025). “How Your Fetus Grows During Pregnancy.” https://www.acog.org/womens-health/faqs/how-your-fetus-grows-during-pregnancy ↩

2. Mayo Clinic. (2024). “Fetal development: The 2nd trimester.” https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/fetal-development/art-20046151 ↩

3. BabyCenter. (2025). “17 weeks pregnant: Symptoms, baby development, and more.” ↩

4. Cleveland Clinic. (2025). “Fetal Development: Week-by-Week Stages of Pregnancy.” https://my.clevelandclinic.org/health/articles/7247-fetal-development-stages-of-growth ↩

5. Parents. (2024). “Second Trimester Fetal Development: Week by Week.” https://www.parents.com/pregnancy/stages/fetal-development/second-trimester-images-of-your-developing-baby/ ↩

6. Mayo Clinic. “Symptoms of pregnancy: What happens first.” https://www.mayoclinic.org/healthy-lifestyle/getting-pregnant/in-depth/symptoms-of-pregnancy/art-20043853 ↩