The third trimester can feel like a countdown with a body that has its own agenda: heavier breathing on the stairs, reflux at the worst possible moment, and a baby who seems to host nightly dance rehearsals. Parents often ask the same questions—how to read fetal movement, what “normal” swelling looks like, when Braxton Hicks becomes labor, and which symptoms should trigger a call. The third trimester also brings more follow-up, more decisions, and, sometimes, more mental load.

Expect a week-by-week sense of direction, clear explanations of medical terms, and practical ways to stay comfortable and safe.

Third trimester basics: dates, due date language, and “term”

The third trimester usually starts at 28 weeks of gestational age and lasts until birth. Gestational age (GA) is counted from the first day of the last menstrual period.

Your estimated due date (EDD) is an estimate around 40 weeks GA, not a deadline. Many healthy births happen between 38 and 42 weeks.

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“Viability” refers to a baby’s chance of survival outside the uterus with neonatal intensive care. In many settings, it’s discussed around 24 weeks GA, with outcomes improving after 28 weeks as lung and brain maturation accelerates.

Term definitions:

Early term: 37+0 to 38+6
Full term: 39+0 to 40+6
Late term: 41+0 to 41+6
Post-term: 42+0 and beyond

Third trimester timeline: what often changes by stage

Every pregnancy differs, but the third trimester often follows a recognizable rhythm.

Weeks 28–31: early third trimester

Baby growth ramps up. Subcutaneous fat increases, and the lungs raise surfactant production (it helps keep tiny air sacs open after birth).

Many parents notice:

Braxton Hicks tightenings (often irregular, easing with rest or hydration)
Heartburn and slower digestion (progesterone relaxes smooth muscle)
Back discomfort and posture changes
Sleep fragmentation

A common topic here: vaccines such as Tdap (often offered between 27–36 weeks, depending on local protocols).

Weeks 32–34: “crowded uterus” weeks

Movements may feel stronger but less acrobatic—more rolls and stretches, fewer flips. Many babies begin spending more time head-down, although position can still change.

Depending on your care pathway, an ultrasound around this period may check fetal growth estimate and growth curves, placenta location, amniotic fluid (AFI or deepest pocket), and presentation.

Weeks 35–37: key tests and position checks

This is a common window for the GBS swab. If positive, antibiotics during labor lower the risk of early newborn infection.

Appointments often become more frequent. Braxton Hicks can intensify—annoying, sometimes painful, yet typically irregular.

Weeks 37–40+: early term to “any day now”

From 37 weeks, pregnancy is considered term. Engagement (baby settling deeper into the pelvis) may increase pelvic pressure and urinary frequency.

Past the due date, clinicians may propose NST/BPP and fluid checks, then discuss induction timing.

Baby development in the third trimester

The third trimester is a phase of rapid refinement.

Growth and body fat

A large share of fetal weight gain happens now. Ultrasound weight estimates use head/abdominal measurements and femur length. Helpful, yes—perfect, no.

Brain and nervous system: myelination

Brain growth accelerates. Myelination (insulating nerve pathways) supports feeding coordination, reflexes, and sleep–wake rhythms.

Lungs: surfactant and practice breathing

Surfactant rises, and “practice breathing” movements occur in amniotic fluid. Earlier births may need respiratory support, later third trimester births generally come with more lung readiness.

Passive immunity: IgG transfer

Maternal IgG antibodies cross the placenta increasingly late in pregnancy, offering temporary newborn protection—especially when vaccination boosts antibody levels.

Skin: vernix and lanugo

Vernix caseosa protects the skin. Lanugo (fine hair) usually thins toward term. Increasing fat also improves temperature regulation.

Amniotic fluid

Too little (oligohydramnios) or too much (polyhydramnios) may lead to closer monitoring.

Position: head-down, breech, engagement

Many babies settle into cephalic presentation (head-down) during the third trimester. If breech persists near term, ECV (external cephalic version) around 36–37 weeks may be discussed.

Fetal movement in the third trimester: patterns, counts, when to call

Space decreases, but movement should remain present and familiar.

What movement can feel like now

In the third trimester, expect fewer flips and more strong rolls, stretches, and kicks. Quiet periods can be fetal sleep.

Kick counts: a simple method

A common approach is 10 movements in 2 hours:

Choose a time your baby is usually active
Lie on your side or sit quietly
Count distinct movements

Decreased fetal movement

Call promptly if you notice a persistent drop from your baby’s usual pattern.

You may be offered:

NST
BPP
Ultrasound assessment of growth, fluid, placenta, and position

Common third trimester symptoms: causes and what can help

Late pregnancy symptoms often come from pressure, hormones, and circulation changes.

Fatigue (and iron deficiency anemia)

Interrupted sleep and increased demands can drain you. Sometimes iron deficiency anemia contributes, blood tests can guide supplementation.

Shortness of breath

The diaphragm has less room. Upright posture, pacing activity, and side-sleeping help.

Seek urgent care for chest pain, fainting, or sudden severe breathlessness.

Heartburn

Progesterone relaxes the lower esophageal sphincter, the uterus adds pressure. Try smaller meals, staying upright after eating, and elevating the upper body at night. Ask about pregnancy-compatible antacids (for example calcium carbonate).

Pelvic pressure and back/pubic pain

As the baby descends, heaviness and pelvic pulling sensations can appear. Support belts (when advised), heat/cold packs, supportive shoes, and prenatal physiotherapy can help. Avoid NSAIDs unless your clinician approves.

Swelling and heavy legs

Mild edema in ankles/feet is common in the third trimester. Walking, leg elevation, and compression stockings (if advised) may help.

Urgent assessment is needed for sudden face/hand swelling, severe headache, vision changes, or one-sided leg swelling with redness/pain.

Constipation, hemorrhoids, urinary changes

Fiber, fluids, and gentle movement are first-line for constipation. Sitz baths and clinician-approved topical care can soothe hemorrhoids. Burning with urination or fever can suggest a UTI.

Hand tingling (carpal tunnel)

Fluid shifts can cause carpal tunnel syndrome symptoms. Wrist splints and sleep positioning may help.

Sleep and emotions

Side-sleeping, pillow support, a cool room, and a calmer routine can improve sleep. If anxiety becomes intrusive or mood drops sharply, bring it up quickly—support exists.

Prenatal care in the third trimester: visits, tests, and monitoring

Many schedules move from every two weeks to weekly near term.

Common checks:

Blood pressure
Weight trends
Urine testing when used
Symptom review
Fetal heart rate (often 110–160 bpm)

Growth checks

Fundal height usually tracks roughly with weeks of pregnancy. If measurements are off, ultrasound can review growth, fluid, placenta, and position.

Key screenings

Glucose testing follow-up if gestational diabetes is diagnosed
GBS swab (often 35–37 weeks)
CBC for anemia (often hemoglobin <11 g/dL in the third trimester)
RhIG around 28 weeks if you are Rh-negative and not sensitized

Extra monitoring

Depending on risk factors, clinicians may use:

NST
BPP
Umbilical artery Doppler when placental insufficiency is suspected

Vaccines in late pregnancy

Vaccines can protect the pregnant person and support newborn protection via transplacental IgG.

Depending on local guidance, options may include:

Tdap (often 27–36 weeks)
Flu vaccine (inactivated)
COVID-19 vaccination/boosters
Maternal RSV vaccine (in some settings)

Skin changes: itching and rashes

Dryness and stretching can itch. Moisturizers and cool compresses help.

Call promptly if itching is intense and widespread—especially on palms and soles, worse at night, or paired with dark urine or yellowing of eyes/skin. This can suggest intrahepatic cholestasis of pregnancy and needs blood tests (including bile acids).

Warning signs in the third trimester: when to seek urgent care

Contact your maternity unit urgently for:

Vaginal bleeding or clots
Suspected rupture of membranes (gush or persistent leak)
Regular painful contractions before 37 weeks
Decreased fetal movement
Severe headache, vision changes, right upper abdominal pain
Sudden swelling of face/hands
Fever or chills
One-sided leg swelling/redness/pain
Chest pain, fainting, severe breathlessness

Labor signs: when it’s becoming “real”

Braxton Hicks are often irregular and may ease with rest, warmth, hydration, or position changes. True labor tends to become regular, closer together, longer, stronger—and it changes the cervix.

Time contractions from the start of one to the start of the next. Many units reference 5-1-1, but follow your local instructions.

If your water breaks, note time, amount, color, odor, and fetal movement pattern, then contact your unit.

Preparing for birth in the third trimester

The third trimester is when planning becomes practical.

Keep birth preferences short and flexible, including pain relief options such as epidural anesthesia.
Induction may be proposed for post-term pregnancy, ruptured membranes without labor, hypertensive disorders, diabetes-related concerns, or fetal growth issues.
If breech persists, ECV may be discussed around 36–37 weeks.
Many parents pack a bag between 32–36 weeks and confirm transport and childcare.

To remember

The third trimester runs from week 28 to birth, “term” ranges guide monitoring.
Baby gains fat, matures brain and lungs, and receives increasing IgG antibodies.
In the third trimester, movement may feel different, but it should remain present, reduced movement is a good reason to call.
Warning signs (bleeding, leaking fluid, fever, severe headache/vision changes, sudden swelling, preterm labor signs) deserve prompt medical attention.

Professionals can help you sort what’s expected from what needs evaluation. You can also download the Heloa app for personalized guidance and free child health questionnaires.

Questions Parents Ask

Is it safe to travel (or fly) in the third trimester?

For many pregnancies, travel can still be possible in the third trimester—especially earlier on. Comfort often becomes the main challenge: more bathroom breaks, swelling, reflux, and fatigue are common, and long sitting can make legs feel heavy. You can consider frequent walking breaks, good hydration, and compression stockings if your clinician agrees. Because airlines and care teams may have their own cut-offs (often around 36 weeks, sometimes earlier for multiples or higher-risk pregnancies), it’s a good idea to ask what applies to your situation and destination. If you have complications (bleeding, high blood pressure, preterm contractions, placenta issues), travel may be discouraged—no guilt, just a safety call.

Is sex safe in the third trimester?

Most of the time, yes—sex is generally safe in late pregnancy if your pregnancy is uncomplicated. It can even help some parents feel more connected and relaxed. Mild cramping or Braxton Hicks after orgasm can happen and usually settles with rest and fluids—reassuringly common. It’s worth contacting your maternity team for personalized advice if there’s vaginal bleeding, leaking fluid, placenta previa, or a history/risk of preterm labor, as pelvic rest may be recommended in those cases.

How much weight gain is “normal” in the third trimester?

There isn’t one perfect number. Weight changes depend on your pre-pregnancy BMI, fluid retention, baby’s growth, and even timing of swelling. Slow, steady gain is common, and sudden jumps can sometimes be just water. If you notice rapid swelling plus symptoms like headache or vision changes, it’s important to check in promptly.

Third trimester: week-by-week timeline and what to expect