13 Weeks Pregnant: Welcome to the Second Trimester

At 13 weeks pregnant, your baby is about the size of a peach (approximately 65-78 mm or 2.6-3.1 inches). Welcome to the second trimester! Morning sickness and fatigue typically improve significantly this week. Your baby’s vocal cords are forming, and proportions are becoming more balanced as the body catches up to the head.¹

What’s Happening at 13 Weeks Pregnant?

Week 13 marks the official start of the second trimester—often called the “honeymoon period” of pregnancy. This trimester (weeks 13-27) is typically the most comfortable phase of pregnancy. Energy returns, morning sickness fades, appetite improves, and you’re not yet large enough to be physically uncomfortable.²

Your baby continues growing rapidly, with the body lengthening and proportions becoming more human-like. The head, which has dominated your baby’s appearance for weeks, is now becoming more proportional to the body as the torso and limbs lengthen.

For you, this week often brings relief from the challenging first-trimester symptoms. Many people feel dramatically better almost overnight as hormone levels stabilize and the placenta fully takes over hormone production.³

How Big is My Baby at 13 Weeks?

Your baby at 13 weeks is about the size of a peach or lemon, measuring approximately 65-78 millimeters (2.6-3.1 inches) from crown to rump and weighing about 23 grams (0.8 ounces).⁴

Your baby has roughly tripled in weight since week 10. Body proportions are shifting, with the head now making up about one-third of total body length (down from one-half in previous weeks).

Baby Development at Week 13

Significant refinement and new capabilities emerge this week:

Proportional development: Your baby’s body is catching up to the head in size. Arms are lengthening to a more proportional length, and legs are continuing to grow (though they’re still shorter than arms at this point).

Vocal cord formation: Your baby’s vocal cords are developing in the larynx. While your baby won’t use them until after birth, these structures are forming now and will enable your baby’s first cry.⁵

Facial development: Features are becoming more defined and unique:

• Ears have moved to their final position on the sides of the head
• Eyes are moving closer together (previously wide-set)
• The nose is more prominent
• The chin is more defined
• Lips are fully formed

Movement and reflexes: Your baby is incredibly active:

• Sucking thumb and fingers
• Swallowing amniotic fluid
• Yawning
• Hiccuping
• Stretching and kicking
• Making faces—frowning, grimacing, squinting⁶

Digestive system: The intestines are moving from the umbilical cord into the abdominal cavity and are practicing wave-like contractions (peristalsis) that will move food through the digestive tract after birth.

Urinary system: Kidneys are producing urine continuously, which is released into the amniotic fluid. Your baby swallows this fluid, and the cycle continues—an important process for kidney and lung development.

Skeletal system: Bones are continuing to harden, especially in the skull and long bones. The skeleton is becoming more defined and sturdy.

Sex organs: If you’re having a boy, the prostate is developing. If you’re having a girl, ovaries contain about 2 million eggs (this number will decrease to about 1-2 million by birth). External genitalia may be visible on ultrasound in some cases.

Placenta: The placenta is fully functional and has taken over hormone production from your ovaries—a transition that often corresponds with decreased nausea and fatigue.

Fine hair: Very fine hair (lanugo) may begin covering your baby’s body. This hair helps regulate body temperature and will be shed before or shortly after birth.

Fingerprints: The unique ridges that form fingerprints are completely developed.

Common Symptoms at 13 Weeks Pregnant

Week 13 typically brings welcome improvements in symptoms:⁷

Decreased or eliminated morning sickness: Most people experience significant relief from nausea and vomiting this week. For some, symptoms disappear entirely. A small percentage continue experiencing nausea into the second trimester.

Increased energy: Fatigue typically lifts as the placenta takes over hormone production. You may feel much more like your pre-pregnancy self.

Increased appetite: As nausea fades, appetite often returns with intensity. Your body needs additional calories to support your growing baby.

Visible baby bump: Your uterus is rising out of the pelvis and into the abdomen, creating a visible bump for many people. You may need maternity clothes or elastic-waist options.

Less frequent urination: As your uterus moves upward out of the pelvis, pressure on your bladder decreases temporarily, reducing bathroom trips.

Improved mood: Hormonal stabilization and physical symptom relief often lead to better mood and emotional well-being.

Increased libido: For many people, sex drive returns in the second trimester after disappearing during the challenging first trimester.

Heartburn and indigestion: As your uterus expands, it can push stomach acid upward, causing heartburn. This symptom may persist throughout pregnancy.

Constipation: Progesterone continues slowing digestion, and your growing uterus puts pressure on your intestines.

Round ligament pain: You may feel sharp, brief pains on one or both sides of your lower abdomen as ligaments stretch to support your growing uterus.

Increased vaginal discharge: Thin, milky discharge is normal and continues throughout pregnancy.

Skin changes: The pregnancy “glow” (radiant skin) is common in the second trimester. Some people develop melasma (dark patches on the face) or linea nigra (a dark line down the abdomen).

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)
• Sudden swelling of hands, feet, or face
• Severe headache with vision changes
• Decreased fetal movement (in later pregnancy)

Tips for Week 13

Embrace the second trimester: Enjoy this often-wonderful phase of pregnancy when you feel good, have energy, and can still move comfortably.

Start or maintain exercise: With returning energy, regular gentle exercise can boost mood, maintain healthy weight gain, and improve overall pregnancy health. Walking, swimming, prenatal yoga, and strength training are great options.

Eat nutritiously: With improved appetite, focus on nutrient-dense foods: lean proteins, fruits, vegetables, whole grains, healthy fats, and calcium-rich foods. You need about 300-350 extra calories daily in the second trimester.

Stay hydrated: Continue drinking 8-10 glasses of water daily to support increased blood volume and prevent constipation.

Consider maternity clothes shopping: As your bump becomes visible, invest in comfortable, well-fitting maternity clothes. Supportive maternity pants and flowing tops can make a big difference.

Address heartburn: Eat small, frequent meals; avoid spicy, fatty, or acidic foods; don’t lie down immediately after eating; and sleep with your head elevated.

Prevent constipation: Increase fiber, drink plenty of water, stay active, and ask your doctor about safe stool softeners if needed.

Schedule your anatomy ultrasound: The detailed anatomy scan typically happens at weeks 18-20. Call your provider’s office to schedule it.

Consider prenatal classes: Research and register for childbirth education, breastfeeding, newborn care, or infant CPR classes.

Connect with other pregnant people: Join a pregnancy group, online community, or prenatal class to connect with others at similar stages.

Enjoy intimacy: If you’re feeling better and interested, the second trimester is often a great time for intimacy with your partner (unless your doctor has advised otherwise).

Tracking Your Pregnancy with Nooko

At 13 weeks pregnant, you’re entering the second trimester—a new chapter in your pregnancy journey. Tracking this transition helps you appreciate the positive changes ahead and stay connected to your baby’s development.

With Nooko, you can document the shift from challenging first-trimester symptoms to the more comfortable second trimester. Log when morning sickness finally ends and energy returns—milestones worth celebrating. Track your growing bump with weekly photos and measurements.

Access information about your baby’s weekly development, including new capabilities like vocal cord formation. Set nutrition and exercise goals for the second trimester. Plan for upcoming milestones like finding out your baby’s sex and feeling first movements. Download Nooko to make the most of your second-trimester “honeymoon period.”

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

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References

Footnotes

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

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. Johns Hopkins Medicine. (2024). “The First Trimester.” https://www.hopkinsmedicine.org/health/wellness-and-prevention/the-first-trimester ↩

4. Medical News Today. (2023). “13 weeks pregnant: Symptoms, hormones, and baby development.” https://www.medicalnewstoday.com/articles/300000 ↩

5. Cleveland Clinic. (2025). “Fetal Development: Week-by-Week Stages of Pregnancy.” ↩

6. 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 ↩

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