Third Trimester: What to Expect Week by Week (28–40+)

Third Trimester Overview

The third trimester begins at week 28 and ends at birth — typically around week 40, though anywhere from 37 to 42 weeks is considered the normal range. This final stretch is when your baby puts on most of their weight, their lungs mature, and their brain development accelerates dramatically.

For many mothers, the third trimester is physically demanding. The discomforts of the second trimester — heartburn, back pain, swollen feet — intensify as your uterus expands from roughly the size of a basketball to one that holds a full-term baby. Sleep becomes difficult. Braxton Hicks contractions become more frequent. And the mental load of preparing for a new person joins the physical weight.

Weeks 28–31: Early Third Trimester

Week 28

Your baby now weighs about 2.5 pounds (1.1 kg) and measures roughly 15 inches long. Their eyes can open and close, and they can blink. REM sleep has begun, meaning your baby may already be dreaming. Brain development is accelerating — the brain’s characteristic grooves and folds are forming rapidly this week.

For you: Expect increased back pain as your center of gravity shifts further. The recommended sleeping position changes to left side — this improves blood flow to the placenta and reduces pressure on major blood vessels. Your doctor may begin the Rh factor discussion if you’re Rh-negative.

Key appointment: Your glucose screening (if not done at 24–28 weeks) and the beginning of more frequent prenatal visits — every 2 weeks from now.

Week 29

Baby now weighs approximately 2.7 pounds. Their muscles and lungs continue maturing, and they’re gaining fat rapidly under the skin. Your baby can now tell light from dark and may turn toward a bright light shone on your abdomen. Kicks and movements are strong and regular — this is a good time to start kick counts if your provider recommends them.

You may notice increasing shortness of breath as your uterus pushes up against your diaphragm. This is normal but worth mentioning if it’s severe. Hemorrhoids often worsen this trimester — increased pelvic pressure is the culprit.

Week 30

At about 3 pounds and 16 inches, your baby’s bone marrow has fully taken over red blood cell production. Their skin is smoothing out as fat deposits fill in. Lanugo (the fine downy hair that covered their body) is beginning to disappear.

Carpal tunnel syndrome peaks for many pregnant women around this time — the swelling that presses on the median nerve in your wrist causes tingling and numbness in the hands. Wrist splints and avoiding prolonged positions with bent wrists can help.

Week 31

Your baby weighs about 3.3 pounds. All five senses are now functional — they can taste, smell, hear, see, and feel. Their nervous system is sophisticated enough to process sensory information. Brain development is one of the most active phases of any time in human life this week.

Braxton Hicks contractions become more noticeable — practice contractions that tighten and release without causing true labor. They’re usually irregular, don’t intensify over time, and stop with position changes or hydration. True labor contractions do the opposite.

Weeks 32–35: The Final Stretch Begins

Week 32

Baby now weighs about 3.75 pounds and is practicing breathing movements — the lungs are almost fully developed. Their fingernails have grown to the tips of their fingers. Most babies settle into a head-down position this week, though there’s still room to turn.

You may notice your belly has dropped slightly — or not yet, which is equally normal. The nesting instinct often kicks in intensely around weeks 32–34. If you suddenly feel compelled to reorganize every cabinet in your house at 2 AM, welcome to the third trimester.

Week 33

Your baby’s bones are hardening — except for the skull, which remains soft and pliable to ease passage through the birth canal. Their immune system is developing and beginning to receive antibodies through the placenta. Baby weighs about 4.2 pounds.

Sleep disruption intensifies this week for most mothers. Between frequent bathroom trips, difficulty finding a comfortable position, leg cramps, and a baby who may be most active when you’re trying to rest, fragmented sleep becomes the norm. A pregnancy pillow can significantly help with positioning.

Week 34

At approximately 4.7 pounds and 18 inches, your baby’s central nervous system and lungs have matured enough that babies born now have excellent outcomes with medical support. The vernix caseosa — the white waxy coating that protects their skin — thickens this week.

Group B Strep (GBS) testing typically occurs between weeks 35–37. A simple swab of the vagina and rectum, it tests for bacteria that can be harmless in adults but dangerous to newborns during delivery. If positive (about 25% of women are), you’ll receive antibiotics during labor.

Week 35

Your baby weighs about 5.3 pounds. Their kidneys are fully developed and their liver can process some waste. Fat continues to accumulate — they now have the chubby appearance of a newborn. Most of the lanugo has disappeared.

Pelvic pressure increases significantly as the baby engages lower in your pelvis. Many women describe this as “lightning crotch” — sharp, shooting nerve pain in the pelvis, vulva, or thighs as the baby presses on nerves. Uncomfortable but normal.

Weeks 36–40+: Full Term and Beyond

Week 36

Your baby weighs about 6 pounds. Most of the vernix and lanugo have shed into the amniotic fluid. Their digestive system is mature, though they won’t need to use it for real digestion until after birth. Prenatal visits are now weekly.

If your baby is breech (feet or bottom down) at 36 weeks, your provider may discuss options: external cephalic version (ECV), a procedure to manually turn the baby, or planning for a cesarean section. About 96% of babies are head-down by this point.

Week 37

At 37 weeks, your baby is officially “early term.” They weigh about 6.5 pounds. Their grasp reflex is strong. Research has shown that brain development continues significantly through weeks 37–40, which is why elective delivery before 39 weeks is generally discouraged without medical reason.

Cervical changes often begin this week — effacement (thinning) and dilation (opening) can start days or weeks before actual labor. Your provider may check your cervix at weekly visits, though early dilation doesn’t predict when labor will begin.

Week 38

Your baby weighs about 7 pounds and their vocal cords are ready for that first cry. Their meconium — the dark, sticky first stool made of amniotic fluid, mucus, and other materials — has been accumulating and will typically be passed in the first day or two after birth.

Signs of approaching labor to watch for: the mucus plug (a thick, sometimes bloody discharge), increased Braxton Hicks contractions, lower back ache that comes and goes, and a feeling that the baby has dropped (if they haven’t already).

Week 39

Full term. At about 7.3 pounds, your baby is ready. Their lungs and brain are as mature as they’ll be without being outside the womb. Skin is no longer wrinkled — fat has filled it out. Approximately 26% of babies are born in week 39.

Your body is preparing too: the cervix continues to soften and dilate, the baby moves lower, and you may experience the “bloody show” — a small amount of blood-tinged mucus that indicates the cervix is changing. This is normal and not an emergency, but real labor contractions or water breaking warrant a call to your provider.

Week 40 and Beyond

Only about 5% of babies are born exactly on their due date. About 25–30% of pregnancies extend past 40 weeks. If you reach 41 weeks, your provider will typically begin discussing induction, as risks (particularly related to placental function) begin to increase after 42 weeks.

Post-dates monitoring usually includes non-stress tests (measuring the baby’s heart rate in response to movement) and amniotic fluid assessments. These help ensure the baby and placenta are still functioning well while you wait.

Common Third Trimester Symptoms

The third trimester brings a distinct set of physical experiences — some uncomfortable but manageable, others worth mentioning to your provider.

Backache and Pelvic Girdle Pain

As your uterus grows and pregnancy hormones loosen ligaments to prepare for birth, back and pelvic pain intensifies. The hormone relaxin causes joints throughout the pelvis to become more mobile — helpful for birth, uncomfortable in daily life. Prenatal yoga, swimming, a maternity support belt, and sleeping with a pillow between your knees can all provide relief.

Heartburn and Acid Reflux

Your expanding uterus pushes stomach acid upward, and the same hormones that relax your pelvic ligaments also relax the valve between your esophagus and stomach. Eating smaller, more frequent meals, staying upright after eating, and sleeping with your upper body elevated can help. Antacids like Tums and Pepcid are generally safe in pregnancy — confirm with your provider.

Swelling (Edema)

Mild swelling in feet and ankles is normal, especially at the end of the day and in warm weather. Elevate your feet when resting, stay hydrated (counterintuitively, dehydration worsens water retention), and avoid long periods of standing. Sudden or severe swelling — especially in the face or hands — can indicate preeclampsia and requires prompt medical evaluation.

Frequent Urination

As the baby descends and puts pressure on your bladder, bathroom trips increase dramatically. Leakage (stress incontinence) with coughing, sneezing, or laughing is common. Kegel exercises throughout pregnancy help, though the full benefit often emerges postpartum. See our pelvic floor exercises guide for technique and a postpartum plan.

Braxton Hicks Contractions

These “practice contractions” become more frequent and intense in the third trimester. They’re triggered by dehydration, physical activity, full bladder, or baby movement. Unlike true labor contractions, they’re irregular, don’t increase in intensity, and often stop when you change position or drink water. If you have more than 4 in an hour before 37 weeks, call your provider.

Trouble Sleeping

Between physical discomfort, frequent urination, vivid dreams, and pregnancy anxiety, most women report significant sleep disruption in the third trimester. Left-side sleeping is recommended for circulation, but switching sides as needed is fine. A full-length pregnancy pillow that supports your bump and keeps a pillow between your knees can make a meaningful difference.

Shortness of Breath

Your growing uterus displaces your diaphragm upward by up to 4 centimeters, reducing lung capacity. Most women feel some shortness of breath, particularly when exerting themselves. This typically improves when the baby drops (lightening) in the final weeks. Severe or sudden shortness of breath, chest pain, or a racing heart warrant immediate attention.

Your Baby’s Development in the Third Trimester

The third trimester is primarily about growth and final maturation rather than the dramatic structural development of the first trimester.

Brain Development

The brain grows faster during the third trimester than at any other point in development. The cerebral cortex — responsible for thought, emotion, memory, and consciousness — develops its characteristic wrinkled surface (gyri and sulci) during this period. Studies have shown that brain volume nearly doubles between 28 and 40 weeks. This is a primary reason why reaching full term matters even when a baby looks ready earlier.

Lung Maturation

Surfactant — the substance that allows the lungs’ tiny air sacs to stay open after birth — begins production around week 24 but reaches adequate levels only around weeks 34–36 for most babies. Babies born before 34 weeks often need respiratory support; those born between 34–36 weeks may need some support; those born after 37 weeks typically breathe on their own immediately.

Weight Gain

Your baby gains about half a pound per week in the third trimester on average, though growth slows slightly in the final weeks as they run out of room. Brown fat — a specialized fat that generates heat — accumulates rapidly in weeks 36–38, helping your newborn regulate body temperature outside the womb.

Sensory Development

By the third trimester, all five senses are functional. Research shows babies recognize and prefer their mother’s voice from birth — they’ve been hearing it for months. They can distinguish between bitter and sweet tastes in amniotic fluid. They respond to bright light and startle at loud sounds. Your baby is already a sensory being well before birth.

Third Trimester Prenatal Appointments

Prenatal care becomes more frequent in the third trimester as your provider monitors both your health and the baby’s development more closely.

Appointment Schedule

Typically: every 2 weeks from weeks 28–36, then weekly from 36 weeks until delivery. Each visit includes weight, blood pressure, fundal height measurement (uterus size), baby’s heartbeat, and discussion of symptoms and concerns.

Key Tests and Screenings

Glucose tolerance test (if not done): If the one-hour glucose screening at 24–28 weeks was abnormal, a three-hour test follows. Gestational diabetes management begins if diagnosed. See our gestational diabetes diet guide for what this means for your nutrition.

Group B Strep test (35–37 weeks): A vaginal/rectal swab to check for GBS bacteria. Results guide antibiotic use during labor.

Non-stress tests (NST): If you’re post-dates or have any risk factors (gestational diabetes, reduced movement, high blood pressure), your provider may schedule NSTs — monitoring the baby’s heart rate patterns to assess wellbeing.

Biophysical profile (BPP): Combines an NST with ultrasound to assess fetal breathing, movement, muscle tone, and amniotic fluid levels. Often ordered post-dates or when movement has decreased.

Cervical checks: Starting around 36–37 weeks, your provider may check for dilation and effacement, though these exams are optional — dilation in advance doesn’t predict when labor will start.

Preparing for Birth in the Third Trimester

The third trimester is your window to prepare — while you still have the energy and before the baby takes all your attention.

Birth Plan

A birth plan communicates your preferences for labor and delivery — pain management, who’s in the room, interventions, cord clamping, skin-to-skin. It’s not a binding contract but a starting point for conversation with your care team. See our birth plan template to cover all the key decisions without overwhelm.

Childbirth Education

Childbirth classes (Lamaze, Bradley, HypnoBirthing, hospital-based classes) are ideally completed by week 36. Online options are available if in-person isn’t feasible. Understanding labor stages, pain management options, and what to expect reduces fear and helps you make informed decisions in the moment.

Hospital Bag

Pack by week 36 — or earlier if you have any risk factors for early delivery. Your bag should be ready to go at a moment’s notice. See our complete hospital bag checklist for exactly what to bring for you, your partner, and your baby.

Newborn Care Preparation

Install the car seat (and have it inspected if possible — many fire stations offer this service). Set up the bassinet or crib. Stock up on postpartum recovery supplies. If you plan to breastfeed, arrange a lactation consultant visit before birth if possible — having support lined up makes the first week much easier.

Maternity Leave and Logistics

Finalize maternity leave paperwork, short-term disability claims, and any FMLA documentation. Brief your workplace on handoff plans. If you have other children, arrange childcare backup for when labor starts. Line up postpartum help — meals, household tasks, childcare — for the first several weeks.

Third Trimester Warning Signs

Know which symptoms require a call to your provider and which require going to the hospital immediately.

Call Your Provider Promptly

• Decreased fetal movement — fewer than 10 movements in 2 hours when you’re focused on counting
• Regular contractions before 37 weeks (more than 4–6 per hour)
• Burning or pain with urination (UTI)
• Mild headache that doesn’t resolve with Tylenol
• New or unusual vaginal discharge
• Pelvic pressure that feels like the baby is pushing out

Go to the Hospital Immediately

• Severe or sudden swelling in face, hands, or feet (may indicate preeclampsia)
• Severe headache, vision changes (spots, blurring, flashing lights), upper right abdominal pain — signs of severe preeclampsia or HELLP syndrome
• Vaginal bleeding (more than light spotting)
• Water breaking (rupture of membranes)
• Fever over 100.4°F
• Chest pain or difficulty breathing
• Severe abdominal pain that doesn’t come in waves
• Signs of labor (regular, increasingly intense contractions)

Frequently Asked Questions