Week 13 of Pregnancy
Learn about your baby's development and what to expect at 13 weeks pregnant.
Baby's Size This Week
Baby Development at Week 13
- ● Your baby is about 7.4 cm long and weighs approximately 23g — about the size of a lemon.
- ● The skeleton is transitioning from soft cartilage to hardening bone, starting in the long bones of the arms and legs.
- ● Vocal cords are fully formed, and facial muscles now allow for expressions like squinting, frowning, and grimacing.
- ● The intestines are producing meconium — the dark, tarry substance that will be your baby's first bowel movement after birth.
- ● Fingerprints are forming in the skin ridges of each fingertip, creating a unique pattern that will remain for life.
- ● If your baby is female, the ovaries already contain approximately 2 million eggs — the full lifetime supply.
Your Body at Week 13
- ● Welcome to the second trimester — many women experience a welcome burst of energy and significant reduction in nausea.
- ● Your belly is becoming more noticeable, and you may start needing maternity pants with a stretchy waistband.
- ● Skin changes like the pregnancy glow (from increased blood flow and oil production) may become more apparent.
- ● The linea nigra (dark vertical line on the abdomen) and darkening of areolas may become visible due to increased melanin.
- ● Round ligament pain — brief, sharp pains on the sides of the lower abdomen — may occur with sudden movements or sneezing.
- ● Your libido may begin to return as nausea fades and energy levels improve in the second trimester.
Week 13 Checklist
- ☐ Celebrate reaching the second trimester — the miscarriage risk has dropped to about 2-3% with a confirmed heartbeat.
- ☐ Begin shopping for maternity clothes if your regular wardrobe is becoming uncomfortable.
- ☐ Stay active with low-impact exercises like walking, swimming, or prenatal yoga (aim for 150 minutes per week).
- ☐ Focus on iron-rich foods (lean meat, beans, fortified cereals, spinach) to prevent anemia as blood volume increases.
- ☐ Start moisturizing your belly with lotion or oil to support skin elasticity as your bump grows.
- ☐ Research childbirth education classes and register early — popular classes fill months in advance.
Frequently Asked Questions
Why do I feel so much better in the second trimester?
The second trimester is often called the 'golden period' of pregnancy. hCG levels have stabilized (reducing nausea), the placenta has taken over hormone production, and your body has adapted to pregnancy hormones. Energy levels typically rise, morning sickness fades, and emotional well-being improves. Enjoy this period — it is a great time for travel, exercise, and preparation.
Is round ligament pain dangerous?
No, round ligament pain is a normal part of pregnancy. The round ligaments support the uterus and stretch as it grows, causing brief, sharp or jabbing pains on one or both sides of the lower abdomen. It is most common during quick movements, sneezing, or coughing. Rest, change positions slowly, and use a warm compress for relief. Contact your provider if pain is constant, severe, or accompanied by fever or bleeding.
When can I find out my baby's sex by ultrasound?
The anatomy scan ultrasound (typically between 18-22 weeks) is the most reliable time to determine sex. NIPT blood testing can reveal sex as early as 10 weeks with high accuracy. Some ultrasound technicians may offer an educated guess as early as 14-16 weeks, but accuracy improves significantly after 18 weeks.
Should I be concerned about the linea nigra?
Not at all. The linea nigra is a dark vertical line that appears on the abdomen during pregnancy due to increased melanin production from hormonal changes. It typically appears around weeks 12-14 and fades within a few months after delivery. It has no medical significance and is purely cosmetic. Sun exposure can make it darker, so use sunscreen on your belly.
Is it safe to sleep on my stomach or back in the second trimester?
Sleeping on your stomach becomes uncomfortable as your bump grows and is generally fine until it feels awkward — usually by mid-second trimester. Sleeping on your back is generally safe until around 20 weeks, but after that it is recommended to sleep on your left side, as this optimizes blood flow to the uterus and prevents the uterus from compressing the inferior vena cava. A pregnancy pillow between your knees can make side sleeping more comfortable.
Track Your Exact Pregnancy Week
Use our free Pregnancy Week Tracker to find out exactly how far along you are based on your last menstrual period or due date.
Track My Pregnancy →Sources
- ACOG
- WHO Fetal Growth Charts
- Mayo Clinic
Medical disclaimer: This content is for informational purposes only and is not intended as medical advice. Always consult a qualified healthcare provider for guidance specific to your pregnancy.