GUIDE
Third Trimester Guide
The final stretch — weeks 28 through 40+ — when your baby gains most of their birth weight and you prepare for delivery.
The third trimester is all about growth, preparation, and anticipation. Your baby will roughly triple in weight during these final weeks, gaining the fat stores needed for life outside the womb. For you, this means more frequent prenatal visits, new physical challenges, and the exciting process of getting ready to meet your baby.
Be prepared from day one
What Happens in the Third Trimester
The third trimester spans weeks 28 through 40 (and sometimes beyond) and is defined by rapid growth and final preparation for birth. Your baby will roughly triple in weight during these weeks, going from about 2.5 pounds at week 28 to an average of 7-8 pounds at birth. Most of this weight gain is fat — the insulating layer your baby needs to regulate body temperature after birth.
For you, the third trimester brings a new set of physical challenges. Braxton Hicks contractions become more frequent, insomnia makes rest harder to come by, and swollen feet become a daily reality. Your baby's increasing size puts pressure on your bladder, diaphragm, and lower back.
Prenatal visits increase to every two weeks from week 28, then weekly from week 36. Your provider will monitor blood pressure closely, check fetal position, and watch for signs of complications. The Group B strep test happens between weeks 36-37.
This is also when you shift into active preparation mode — packing your hospital bag, finalizing your birth plan, and learning to recognize the signs of labor.
| Week | Baby Size | Key Development |
|---|---|---|
| Week 28 | Eggplant | Third trimester begins — baby can blink and dream (REM sleep) |
| Week 29 | Butternut squash | Brain surface developing folds — muscles and lungs maturing |
| Week 30 | Cabbage | Baby gaining about half a pound per week — red blood cell production |
| Week 31 | Coconut | All five senses functioning — baby can track light through the womb |
| Week 32 | Jicama | Toenails and fingernails fully formed — practicing breathing |
| Week 33 | Pineapple | Bones hardening (except skull) — immune system developing |
| Week 34 | Cantaloupe | Lungs nearly mature — vernix coating thickening |
| Week 35 | Honeydew melon | Baby gaining fat rapidly — kidneys fully developed |
| Week 36 | Romaine lettuce | Baby may drop into pelvis (lightening) — head-down position |
| Week 37 | Swiss chard | Early term — baby is practicing sucking and swallowing |
| Week 38 | Leek | Full term begins — brain and lungs continue final maturation |
| Week 39 | Watermelon | Full term — baby is ready for birth, gaining last ounces of fat |
| Week 40 | Pumpkin | Due date week — only 5% of babies arrive on the exact due date |
Month-by-Month Breakdown
The third trimester covers months 7 through 9 of pregnancy.
During month 7 (weeks 28-31), the third trimester begins. Your baby's brain is developing rapidly, all five senses are functioning, and kick counts become an important daily habit. Prenatal visits shift to every two weeks.
At month 8 (weeks 32-35), your baby is gaining weight fast — about half a pound per week. Braxton Hicks contractions become more noticeable, and this is the ideal time to pack your hospital bag and finalize your birth plan. The lungs are approaching full maturity.
By month 9 (weeks 36-40), you are in the home stretch. Weekly visits begin, the Group B strep test is done, and your baby may drop into your pelvis in preparation for birth. You will be watching for the signs of labor — regular contractions, water breaking, and the mucus plug.
Common Third Trimester Symptoms
- Braxton Hicks contractions — irregular uterine tightening that increases in frequency
- Insomnia and difficulty finding a comfortable sleeping position
- Swollen feet and ankles, especially in warm weather or after standing
- Shortness of breath as the uterus pushes against the diaphragm
- Frequent urination — baby pressing on the bladder as they drop lower
- Back pain and pelvic pressure from the baby's weight
- Heartburn and acid reflux intensifying
- Lightning crotch — sudden sharp pains in the pelvis or vagina
- Nesting urge — a strong desire to organize and prepare the home
- Increased vaginal discharge
Third-trimester symptoms are a sign your body is preparing for birth. Talk to your provider about managing discomfort.
Preparing for Labor and Delivery
The third trimester is when labor preparation becomes a priority. Understanding what to expect can reduce anxiety and help you feel more confident.
Learn the signs of labor so you know when it is time to head to the hospital or birth center. Key signs include regular contractions that get closer together, your water breaking, and the loss of your mucus plug.
Understanding the stages of labor — from early labor through delivery of the placenta — helps you know what to expect during the process. Each stage has distinct characteristics and different coping strategies.
Create a birth plan to communicate your preferences to your care team. Include your thoughts on pain management, labor positions, who you want in the room, and your preferences for immediate postpartum care.
Pack your hospital bag by week 35-36. Having it ready removes one source of stress when labor begins.
Week-by-Week Guides
For detailed information about each week in the third trimester, explore the individual guides below.
Week 28 marks the official start of the third trimester. Week 29 and Week 30 bring rapid weight gain and brain development. Week 31 is when all five senses are functional.
Week 32 and Week 33 see the bones hardening and immune system building. Week 34 and Week 35 bring near-mature lungs and rapid fat accumulation.
Week 36 is when baby may drop into the pelvis. Week 37 is early term. Week 38 begins the full-term window. Week 39 is truly full term, and Week 40 is your due date week. For overdue pregnancies, see week 41 and week 42.
When to Call Your Doctor
- Regular contractions before 37 weeks — could indicate preterm labor
- Leaking fluid (a gush or continuous trickle) — possible ruptured membranes
- Vaginal bleeding
- Significant decrease in fetal movement
- Severe headache with visual changes or upper abdominal pain — possible preeclampsia
- Sudden severe swelling in face or hands
In the third trimester, certain symptoms require immediate evaluation. Do not wait for your next scheduled appointment if you experience any of these.
Looking Back and Looking Ahead
You have come a long way from the first trimester and the second trimester. The finish line is in sight.
For managing specific third-trimester symptoms, see our guides on back pain, heartburn, and insomnia. And remember — every uncomfortable symptom is a sign that your body is doing exactly what it needs to do to bring your baby safely into the world.
This guide is for informational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider with any questions about your pregnancy.
