18 Weeks Pregnant: Anatomy Scan Week

At 18 weeks pregnant, your baby is about the size of a bell pepper (approximately 140-150 mm or 5.5-5.9 inches). This week (or next) typically brings your anatomy ultrasound—a detailed scan that examines your baby’s development and may reveal your baby’s sex. Your baby can yawn, hiccup, and hear sounds clearly.¹

What’s Happening at 18 Weeks Pregnant?

Week 18 often brings one of the most anticipated appointments of pregnancy: the anatomy scan (also called the 20-week ultrasound, though it’s typically performed between weeks 18-22). This detailed ultrasound examines your baby’s organs, bones, and overall development to ensure everything is progressing normally. It’s also when many people find out their baby’s sex if they choose to know.²

Your baby is very active now, moving frequently throughout the day. If you haven’t felt movements yet, you likely will within the next week or two. These movements are becoming stronger and more coordinated, and you may notice patterns—times of day when your baby is particularly active.

For you, pregnancy is likely feeling very real. Your bump is visible, you may be feeling movements, and you’re approaching the halfway point of your pregnancy journey.

How Big is My Baby at 18 Weeks?

Your baby at 18 weeks is about the size of a bell pepper or sweet potato, measuring approximately 140-150 millimeters (5.5-5.9 inches) from crown to rump and weighing about 190-200 grams (6.7-7 ounces).³

Your baby is gaining about 1-2 ounces per week now as fat continues accumulating beneath the skin.

Baby Development at Week 18

Remarkable capabilities and refinements characterize this week:

Yawning: Your baby can now yawn—a behavior visible on ultrasound and possibly related to brain development or oxygen regulation.⁴

Hiccuping: Your baby experiences regular hiccups as the diaphragm develops and practices contracting. You might feel these as rhythmic, repetitive movements later in pregnancy.

Advanced hearing: Your baby can hear sounds clearly now—your voice, your heartbeat, music, external noises. Some research suggests babies can distinguish different voices and may even respond to familiar sounds after birth.

Protective coating: Vernix caseosa, a white, creamy substance, is beginning to coat your baby’s skin. This protective covering prevents the skin from becoming waterlogged from constant exposure to amniotic fluid and provides lubrication during birth.

Sleep cycles: Your baby is developing patterns of sleeping and waking, though these don’t yet correspond to day and night. Your baby may sleep 20-30 minutes at a time.

Active movement: Your baby moves frequently:

• Kicking, punching, rolling, and somersaulting
• Grasping the umbilical cord
• Touching face and body
• Sucking thumb
• Stretching and yawning⁵

Sensory development:

• Hearing: Fully functional; can hear and may respond to sounds
• Taste: Actively tasting amniotic fluid
• Touch: Sensitive throughout the body
• Vision: Can detect light but eyes remain closed

Nervous system maturation: Nerves are becoming insulated with myelin, which speeds up communication between nerve cells and improves coordination.

Reproductive development: If you’re having a girl, her uterus and fallopian tubes are formed and in position. If you’re having a boy, his genitals are distinct enough to see on ultrasound.

Bone marrow: Taking over red blood cell production from the liver and spleen.

Common Symptoms at 18 Weeks Pregnant

Week 18 typically brings continued second-trimester comfort:⁶

Feeling movements: Most first-time parents feel first movements between weeks 18-20. If this isn’t your first pregnancy, you may have been feeling movements for weeks.

Growing bump: Your bump is likely obvious now, and you may notice your belly button starting to protrude.

Good energy: Most people still feel energetic during this phase.

Increased appetite: Your baby is growing rapidly and needs additional nutrition.

Lower back pain: As your belly grows and your posture changes, back pain may increase.

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

Leg cramps: May continue, especially at night.

Heartburn: Ongoing as your uterus expands.

Dizziness: Occasionally, especially when standing up quickly.

Increased vaginal discharge: Normal and protective.

Skin changes: Darkening of certain areas (areolas, linea nigra) or the pregnancy glow.

Swollen feet: Mild swelling (edema) is common, especially at the end of the day.

Forgetfulness: “Pregnancy brain” (difficulty concentrating or remembering) is common and normal.

When to Call Your Doctor

Contact your healthcare provider if you experience:

• Heavy bleeding
• Severe abdominal pain
• Fever above 100.4°F (38°C)
• Sudden severe headache with vision changes
• Sudden severe swelling of hands, feet, or face
• No fetal movement for an extended period (if you’ve been feeling regular movements)

Tips for Week 18

Attend your anatomy scan: This detailed ultrasound examines your baby’s organs, limbs, brain, heart, and overall development. The sonographer will measure your baby, check the placenta and amniotic fluid, and look for any signs of abnormalities.⁷

Decide about learning baby’s sex: If you want to know your baby’s sex, the anatomy scan is typically when it can be reliably determined (if baby cooperates with positioning).

Ask questions at your ultrasound: Don’t hesitate to ask the sonographer to explain what you’re seeing or to point out specific features.

Request ultrasound photos: Most facilities provide photos, but ask if you want specific images.

Address back pain: Continue good posture, supportive shoes, gentle exercise, and consider prenatal massage or chiropractic care.

Elevate swollen feet: Rest with feet elevated, avoid prolonged standing, wear compression socks, and stay well-hydrated.

Stay active: Continue regular exercise to maintain strength and flexibility.

Sleep on your left side: This position optimizes blood flow to your baby.

Practice pelvic floor exercises: Kegels help strengthen muscles that support your bladder, uterus, and bowels.

Start planning nursery: With the anatomy scan providing reassurance about your baby’s development, this is a great time to start preparing the nursery.

Consider announcing baby’s sex: If you find out and want to share, plan a fun way to announce the news.

Tracking Your Pregnancy with Nooko

At 18 weeks pregnant, you’re likely having your anatomy scan—a major milestone that provides detailed information about your baby’s development. Tracking this appointment and your baby’s measurements helps you appreciate how much your baby has grown.

With Nooko, you can document your anatomy scan results, including measurements, photos, and any information about your baby’s position or sex. Log when you feel movements and note patterns—times of day when baby is most active. Track symptoms like back pain or swelling to identify effective remedies.

Access detailed information about what your baby can do at 18 weeks, including hearing your voice and yawning. Take weekly bump photos to visualize your changing body. Celebrate reaching the halfway point of pregnancy (coming up at week 20). Download Nooko to make your pregnancy journey well-documented and memorable.

Download Nooko on the App Store | Get Nooko on Google Play

---

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. NCBI. (2023). “Sonography 2nd Trimester Assessment, Protocols, and Interpretation.” StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK570574/ ↩

3. BabyCenter. (2025). “18 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. Mayo Clinic. (2024). “Fetal development: The 2nd trimester.” https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/fetal-development/art-20046151 ↩

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

7. Cleveland Clinic. (2023). “20 Week Ultrasound (Anatomy Scan): What To Expect.” https://my.clevelandclinic.org/health/diagnostics/22644-20-week-ultrasound ↩