Week 31: Development of the Immune System
The thirty-first week is a time of active development of your baby's immune system.
Baby size: Pineapple (125-130 mm)
Baby development
Little Genius Gaining Weight
Your baby continues to grow actively, and most of the energy now goes toward weight gain. The layer of fat helps him look plumper.
What’s happening this week:
- Brain: Development continues, and now the baby can regulate his body temperature.
- Lungs: They continue to mature, but are still not ready for independent breathing.
- Movements: You may notice that movements have become less jerky, but stronger and more stretched — the baby is getting cramped.
- Nails: They have already reached the tips of the fingers.
Your fetus weighs about 1.5 kg, and its length is over 41 cm.
Changes for mom
Practice Contractions and Colostrum Leakage
Your body is actively preparing for birth. You may notice new symptoms that indicate the important day is approaching.
What you may notice:
- Braxton‑Hicks contractions: Irregular uterine tightenings may become more frequent and stronger. This is “practice” before real labor.
- Colostrum leakage: A yellowish fluid may start to appear from your breasts — it’s colostrum, your baby’s first food.
- Back and pelvic pain: It may increase due to the hormone relaxin, which softens the joints.
- Fatigue: Fatigue returns, similar to what you experienced in the first trimester.
It’s important to distinguish practice contractions from real ones. Learn more in the article "Signs of Labor Onset".
Overview
Week 31: All Five Senses at Full Power!
In the thirty-first week your baby is actively using all five senses. He sees light, hears your voice, tastes the amniotic fluid, touches his face, and, theoretically, can smell.
He is now the size of a large coconut. His brain is developing at a lightning‑fast pace, creating trillions of connections. He can already process information and learn — an incredible foundation for future development.
For you, this week is a time when practice contractions may become more frequent, and the discomfort from the size of the belly more noticeable. It’s important to focus on rest and preparing for birth.
Your baby is already a little personality with his own preferences. He may respond to certain music or your voice, indicating his unique development.
You are on the home stretch. To know what to prepare for, read our detailed overview "Third Trimester: What You Need to Know".
Tips for mom
Finalize the Birth Plan and Prioritize Comfort
There’s very little time left, so it’s worth completing all major preparations and focusing as much as possible on yourself.
What to do:
- Finalize your birth plan. Discuss it again with your doctor and partner.
- Buy breast pads. They’ll be needed if colostrum starts leaking.
- Visit a pool or do light gymnastics. This will help reduce strain on your back and joints.
- Plan who will help you after delivery. Arrange with your mother, sister, or friend for assistance in the first weeks.
Creating a birth plan is an important step. Use our article "Birth Plan" as a basis.
Tips for partner
Your Role: Calm, Confidence, and Support
Your calm and confident demeanor is passed on to your partner. Right now you are her main support.
Your contribution to the joint effort:
- Study the birth plan. You should know your partner’s wishes so you can be her voice in the delivery room if needed.
- Be patient. She may find it hard both physically and emotionally. Your patience and love are the best support.
- Help organize assistance. Take charge of communicating with relatives who will help after birth.
- Prepare for partner‑assisted birth. Review breathing and massage techniques, discuss your role.
Your involvement in the birth can greatly ease the process for your partner. Learn more in the article "Partner Births".
Checklist
Your Action Plan for Week 31
On the home stretch!
- ✅ Finalize and print the birth plan.
- 🤱 Buy breast pads and a comfortable nursing bra.
- 🤝 Make a list of helpers for the first weeks after birth.
- 🧘♀️ Continue practicing breathing exercises.
- 👜 Check that everything is packed in the labor bag.
- 📚 Refresh your knowledge about the baby’s first month, by reading the article "First Month of Life Week by Week".