The fetus is starting to put on fat. Until now, the body has been lean and bony, but brown fat is beginning to accumulate under the skin. This fat will be crucial for temperature regulation after birth. The umbilical cord is also growing stronger and thicker. Use our Due Date Calculator to track your timeline.
Key Takeaways
- At 17 weeks, your baby is about 13 cm long (the size of a pear) and weighs roughly 140 grams
- Brown fat (adipose tissue) begins forming this week — it will help the baby regulate body temperature after birth
- Fingerprints are now fully set — completely unique patterns that will never change
- The fetus can hear your heartbeat, digestive sounds, and your voice as muffled vibrations
- Your blood volume has increased by about 40% compared to pre-pregnancy, causing dizziness in some
Your Baby This Week
Size: Pear (about 13 cm, or 5.1 inches)
Weight: About 140 grams
- Fat stores: Brown adipose tissue starts forming. This special fat generates heat and will help the baby stay warm after birth.
- Sweat glands: Developing across the skin
- Umbilical cord: Getting thicker and more durable, with strong blood vessels protected by a jelly-like substance called Wharton's jelly
- Cartilage to bone: The skeleton continues its transformation from soft cartilage to hard bone
- Hearing: Improving. The fetus can hear your heartbeat, digestive sounds, and your voice as a muffled vibration.
- Fingerprints: Fully unique patterns are set by now
The fetus is also practicing sucking and swallowing more frequently, important skills for feeding after birth. Track your baby's growth with our Milestone Tracker.
Your Body
- Increased appetite. You may feel hungrier than usual as the baby grows.
- Stretch marks may start to appear on the belly, breasts, hips, or thighs
- Dizziness from changes in blood pressure, especially when standing up quickly
- Heartburn as the growing uterus pushes stomach acid upward
- Vivid dreams continue for many
Your blood volume has increased by about 40% compared to before pregnancy.
What to Do This Week
- Eat omega-3 fatty acids. DHA supports the baby's brain and eye development. Good sources include salmon, sardines, walnuts, and DHA-fortified eggs. If you do not eat fish, consider a DHA supplement.
- Prepare for the anatomy scan. Your detailed ultrasound during pregnancy is coming up soon, typically between weeks 18 and 22.
- Stand up slowly to prevent dizziness from postural hypotension.
- Stay social. The second trimester is often when people feel their best during pregnancy. Enjoy it.
Common Questions
Why am I getting heartburn?
Progesterone relaxes the valve between your stomach and esophagus, allowing acid to flow upward. The growing uterus adds pressure from below. Eating smaller meals, avoiding spicy or fatty foods, and not lying down right after eating can help.
Are stretch marks preventable?
Stretch marks are largely determined by genetics and how quickly your skin stretches. Moisturizing can reduce itching and may help skin elasticity, but no cream has been proven to prevent them completely. They typically fade from red or purple to silvery white over time.
FAQ
What is brown fat and why does the baby need it?
Brown adipose tissue (brown fat) is a specialized type of fat that generates heat by burning calories. Unlike regular white fat, which stores energy, brown fat is activated in cold environments to warm the body. Newborns have limited ability to shiver, so brown fat is their primary mechanism for staying warm in the first days of life.
Can the baby hear me at 17 weeks?
Yes, partially. The auditory system is now functional enough for the fetus to detect internal sounds — your heartbeat, intestinal gurgles, and your voice as a low, muffled vibration. By weeks 18 to 20, the hearing is developed enough to respond to external sounds and louder noises.
Why do I feel dizzy when standing up?
This is called postural hypotension — a temporary drop in blood pressure when you move from lying or sitting to standing. It is common during pregnancy because blood vessels are relaxed and blood volume is redistributed. Stand up slowly, stay hydrated, and avoid prolonged standing to reduce episodes.
Are stretch marks inevitable?
Stretch marks are primarily determined by genetics and how rapidly the skin stretches. If close family members had them during pregnancy, you are more likely to as well. No topical cream has been proven to prevent them, though moisturizing can reduce itching and improve skin comfort as it stretches.
How much omega-3 does a pregnant person need?
The WHO recommends at least 200 mg of DHA (docosahexaenoic acid) per day during pregnancy. DHA is critical for fetal brain and eye development. Two to three servings of low-mercury fatty fish per week (such as salmon or sardines) typically meets this need. If you avoid fish, a DHA supplement derived from algae is a safe alternative.
Related Articles
- Pregnancy Week-by-Week Overview — see the full timeline
- Pregnancy Week 18: The Baby Can Hear You — what comes next
- Ultrasound During Pregnancy, what to expect at your scans
Sources
- ACOG - Omega-3 Fatty Acids and Pregnancy
- NHS - Week 17 of Pregnancy
- Mayo Clinic - Heartburn During Pregnancy
🔧 Helpful Tools
- Due Date Calculator — Calculate your estimated due date
- Contraction Timer — Track your contractions during labor
- All Baby Tools — Browse all free tools for pregnancy and baby care
