The third trimester runs from week 28 until birth — most major health organizations mark this as the official start point, though it’s sometimes referenced from week 27. This is the final stretch: roughly three months of rapid growth for your baby and steady preparation for you. Here’s what happens week by week.
Weeks 28–31: The Third Trimester Begins
Week 28: Officially the start of the third trimester. Your baby weighs around 2.25 pounds and measures about 14.8 inches, with eyes that can open and close. Movements become stronger and more noticeable as space starts to tighten.
Week 29–30: Your baby’s brain is developing rapidly, forming deeper grooves and folds. Lungs continue maturing and practicing breathing movements by inhaling amniotic fluid.
Week 31: Your baby is roughly the size of a coconut, gaining weight quickly and becoming more responsive to light, sound, and touch.
Weeks 32–34: Settling Into Position
Week 32: Many babies begin turning into a head-down (vertex) position — the ideal position for vaginal delivery. Skin is smoothing out and turning pink as fat fills in underneath. Blood volume is now 40–50% higher than before pregnancy.
Week 33: A clear sleep-wake pattern emerges — pupils close during sleep and open when awake. Bones are hardening everywhere except the skull, which stays soft and flexible for the birth canal.
Week 34: Your baby continues gaining roughly half a pound per week from here on, building the fat stores needed for temperature regulation after birth.
Weeks 35–37: Getting Term-Ready
Weeks 35–36: Your baby continues settling into a head-down position if they haven’t already. Your provider may begin checking positioning at appointments. Around week 36, the Group B strep (GBS) screening typically happens — a quick swab test to check for a common bacterium that can affect newborns during delivery.
Week 37: Your baby is now considered term. All major organs are developed and functioning, though the brain and lungs continue maturing right up until birth.
Weeks 38–40: The Home Stretch
Weeks 38–40: Your baby is fully developed and ready to arrive at any time. Visits shift to weekly, with a closer focus on labor signs, delivery planning, and monitoring your baby’s wellbeing. Pregnancy rarely follows an exact timeline — some babies arrive a bit early, others take their time, and a due date is genuinely an estimate rather than a deadline.
Common Third Trimester Symptoms
Shortness of breath, as the uterus presses on the diaphragm
Braxton Hicks (false) contractions
Frequent urination
Back and hip pain
Heartburn
Swelling in the hands, feet, or ankles
Trouble sleeping
Fatigue
Symptoms tend to ebb and flow — some days feel manageable, others harder, and that variation is completely normal.
Prenatal Visit Schedule
Appointments become more frequent as you approach your due date:
Weeks 28–36: Typically every two weeks
Week 36 onward: Weekly until delivery
These visits check your blood pressure, weight, and your baby’s position, growth, and heartbeat, and give you a regular chance to raise questions or concerns.
Key Third Trimester Tests and Milestones
Glucose tolerance test, if not already completed earlier (typically weeks 24–28)
Group B strep (GBS) test, usually between weeks 36 and 37
Cervical checks, which some providers begin closer to your due date to assess labor readiness
Non-stress tests, sometimes used if you go past your due date, to monitor your baby’s heart rate and movement
Watching for Warning Signs
Call your provider immediately for a severe headache, vision changes, sudden swelling of the face or hands, pain in the upper right abdomen, heavy vaginal bleeding, fluid leaking, or a significant decrease in fetal movement — these can signal preeclampsia, preterm labor, or other complications that need prompt attention.
Third Trimester Checklist
Pack your hospital bag by week 36
Count kicks daily from around week 28
Install and check your infant car seat
Write and discuss your birth plan with your provider
Finalize logistics — route to the hospital, childcare or pet care, and a plan for who to call
FAQ
How many weeks is the third trimester?
The third trimester spans weeks 28 through 40, or until you give birth — roughly the final three months of pregnancy.
How often are prenatal visits in the third trimester?
Typically every two weeks from 28–36 weeks, then weekly from 36 weeks until delivery.
When does the baby turn head-down for birth?
Many babies settle into a head-down position by around week 32, though some don’t fully turn until closer to weeks 35–36.
What is the Group B strep test and when is it done?
It’s a screening for a common bacterium that can affect newborns during delivery, typically performed between weeks 36 and 37 via a quick vaginal-rectal swab.
Is it normal to feel short of breath in the third trimester?
Yes — as your uterus grows and presses against the diaphragm, shortness of breath is a common and expected symptom in the final trimester.
