Third Trimester Guide: Weeks 28–40 — What to Expect and How to Prepare

The third trimester is the final stretch of pregnancy — weeks 28 through 40 and beyond. It is the period of most rapid weight gain for the baby, the most significant physical demands on the mother's body, and the time when birth preparation moves from theoretical to practical. It can also be the most tiring, uncomfortable, and emotionally charged trimester.

This guide covers what your baby is doing week by week during this period, what is happening in your body, which symptoms are expected and which are warning signs, what your antenatal appointments involve, and how to prepare practically and emotionally for birth.

Fact-Checked & Transparent: This article is fact-checked against current CDC, WHO, ACOG, and NHS guidelines. All health information is based on authoritative medical sources. Last verified: June 2026.

⚠️ MEDICAL DISCLAIMER

This article is educational information only. It is NOT a substitute for professional medical advice, diagnosis, or treatment.

Always consult your pediatrician or healthcare provider before making any medical decisions for your baby or child. Every baby is unique, and professional medical guidance is essential.

In case of emergency, call 911 or your local emergency number.

Baby Development: Weeks 28–40

Weeks 28–32: Brain Growth and Lung Maturation

At 28 weeks, your baby's brain is undergoing rapid development. The characteristic folds and grooves of the cerebral cortex begin forming in earnest during this period. The lungs are still maturing but have reached a stage where, with neonatal support, survival outside the womb is possible. This is why 28 weeks is recognised as a significant milestone.

Week 28 is the threshold of legal viability in most countries. Babies born at this gestation face serious challenges and require intensive NICU care, but survival rates have improved substantially over recent decades.

By 32 weeks, survival rates with NICU care are significantly better — around 95% in well-resourced settings. The baby is putting on white fat beneath the skin, which both insulates and gives the characteristic rounded appearance of a full-term newborn. Lanugo — the fine hair covering the body — begins to shed. The baby can track light and startle at loud sounds.

Weeks 33–36: Finishing Touches

The lungs continue maturing. A substance called surfactant, which prevents the air sacs from collapsing between breaths, is produced in increasing quantities. By around 36 weeks, most babies have sufficient surfactant for breathing independently, though some late preterm babies (34–36 weeks) still need respiratory support.

The baby's immune system receives a boost as maternal antibodies cross the placenta, providing passive immunity for the first months of life.

At around 36 weeks in a first pregnancy, the baby's head typically descends into the pelvis — a process called engagement or "lightening." This can happen later in subsequent pregnancies, sometimes not until labour has already begun.

Week 37: Term

At 37 weeks, a pregnancy is officially at term. The baby's organ systems are mature and ready for life outside the womb. Babies born from this point are not considered preterm, though 39–40 weeks remains the optimal gestational age for delivery in the absence of complications.

Week 40: Estimated Due Date

The estimated due date (EDD) is calculated at 40 weeks from the first day of the last menstrual period (or adjusted based on first-trimester ultrasound). Only around 5% of babies arrive on their EDD. Most arrive within two weeks either side.

What Is Happening in Your Body

Fundal Height Measurements

At each antenatal appointment, your midwife will measure fundal height — the distance from the top of your pubic bone to the top of your uterus in centimetres. This measurement roughly corresponds to gestational age in weeks. If the measurement is significantly smaller or larger than expected, you may be referred for an ultrasound to check fetal growth and amniotic fluid volume.

Braxton Hicks Contractions

Braxton Hicks contractions — sometimes called "practice contractions" — become more frequent and noticeable in the third trimester. They are irregular, generally painless or mildly uncomfortable, and do not increase in frequency or intensity over time. They are not a sign of labour. If contractions become regular, increase in intensity, or are accompanied by other symptoms, contact your midwife.

Engagement

In first pregnancies, the baby's head typically engages in the pelvis around 36 weeks. You may notice that your bump looks or feels lower and that breathing becomes easier — this is called "lightening." At the same time, pressure on the bladder typically increases, and the urge to urinate becomes more frequent.

Physical Changes

As the uterus continues to grow, it pushes the diaphragm upward, causing breathlessness even at rest. The centre of gravity shifts forward, increasing lower back strain. Fluid retention increases, commonly causing swelling in the feet, ankles, and hands, particularly at the end of the day or in warm weather.

Common Third Trimester Symptoms

Back Pain and Pelvic Girdle Pain

Back pain is almost universal in the third trimester. The expanding uterus shifts the centre of gravity forward, placing sustained load on the lower back muscles. Pelvic girdle pain (PGP) — formerly called symphysis pubis dysfunction — affects a significant minority of pregnant women and can be severely limiting. PGP causes pain in the front or back of the pelvis and is worsened by activities that involve weight-bearing on one leg, such as climbing stairs or turning in bed. Referral to a women's health physiotherapist is the most effective treatment.

Heartburn

As the uterus expands, it pushes the stomach upward and increases reflux. Heartburn is extremely common in the third trimester. Eating smaller, more frequent meals, remaining upright for an hour after eating, and sleeping with the head of the bed slightly elevated can help. Antacids that are safe in pregnancy (such as calcium carbonate-based products) are widely available — check with your pharmacist or midwife if you are unsure which products are appropriate.

Swollen Feet and Ankles

Mild oedema (swelling) in the feet and ankles in the evening is common and generally benign. Elevating the feet, wearing comfortable footwear, and staying active all help. However, sudden or severe swelling — particularly if accompanied by headache, visual changes, or upper abdominal pain — can be a sign of pre-eclampsia and requires urgent assessment.

Itchy Skin

General skin itching over the bump is common as the skin stretches. However, persistent itching — particularly of the palms and soles, and especially at night — can indicate obstetric cholestasis, a liver condition that carries risks for the baby. Report unusual or persistent itching to your midwife.

Sleeplessness

Sleep becomes increasingly difficult in the third trimester due to physical discomfort, the need to urinate frequently, the baby's movements at night, and anxiety about the approaching birth. Sleeping on the left side with a pillow between the knees reduces pressure on the inferior vena cava and is generally more comfortable. Specialist pregnancy pillows that support the bump and back can help.

Braxton Hicks, Haemorrhoids, and Varicose Veins

Constipation and straining increase the risk of haemorrhoids (piles) in the third trimester, as does the increased pressure of the uterus on the pelvic veins. Staying hydrated, eating sufficient fibre, and not straining are the main preventive measures. Similarly, varicose veins in the legs and vulva are common due to increased blood volume and pelvic pressure. Compression stockings and regular movement help.

Antenatal Appointments in the Third Trimester

28-Week Appointment

At 28 weeks, your midwife will check blood pressure, test urine for protein, measure fundal height, check the baby's position, and offer a blood test for anaemia and blood type antibodies. If you are rhesus negative, anti-D injections will be offered at 28 weeks to prevent rhesus sensitisation.

34-Week Appointment

Blood pressure, urine, and fundal height checks continue. Your midwife will discuss birth options, the signs of labour, and when to call or go to hospital. This is a good appointment to raise questions about birth plans and pain relief options.

36-Week Appointment

At this appointment, your midwife will check the baby's position — specifically whether the head is down (cephalic) or whether the baby remains in a breech or transverse position. If the baby is not head-down by 36 weeks, you will typically be referred for an ultrasound and offered a discussion about external cephalic version (ECV), a procedure where a doctor manually attempts to turn the baby from the outside.

In the United States, a Group B Streptococcus (GBS) swab is routinely offered between 35 and 37 weeks. GBS can cause serious infection in newborns and the swab result guides antibiotic treatment during labour.

38-Week Appointment

Blood pressure, urine, and fundal height. This appointment typically involves discussion about what to expect in the final weeks, signs to watch for, and a review of your birth plan.

40-Week Appointment and Beyond

If you reach 40 weeks without delivering, you will have an appointment to discuss your options. Most UK hospitals offer membrane sweeping from 40 weeks — a vaginal examination in which the midwife gently separates the membranes from the cervix to stimulate prostaglandin release. This can help trigger the onset of labour and may reduce the need for formal induction.

Preparing for Birth

Birth Plan

A birth plan is not a binding contract — it is a document that helps communicate your preferences to the staff caring for you during labour. It typically covers your preferences around pain relief, monitoring, positions, who you want present, what you want to happen immediately after birth (delayed cord clamping, skin-to-skin contact, vitamin K for the baby), and any specific concerns or wishes. Most maternity units welcome birth plans.

Hospital Bag

Packing your hospital bag from around 36 weeks means you are prepared if labour starts early. The bag typically includes: your maternity notes, identity documents, birth plan, comfortable clothing, maternity pads, breast pads, toiletries, snacks and drinks, a car seat for the journey home, and clothes for the baby.

Understanding Your Pain Relief Options

The main pain relief options available during labour include: gas and air (Entonox — available in all birth settings), pethidine or diamorphine injections, an epidural (which provides the most complete pain relief but requires an IV cannula and continuous fetal monitoring), TENS machines (useful in early labour), water (a birthing pool or bath), and non-pharmacological techniques including breathing techniques, movement, heat, and massage. Discuss your preferences and any questions with your midwife before labour begins.

Birth Choices

Depending on your pregnancy risk profile and your preferences, you may choose to give birth in a hospital delivery suite, a midwife-led unit, or at home. The NHS publishes data on safety outcomes for these different settings. For low-risk pregnancies in subsequent births, midwife-led units and home birth are safe options supported by good evidence. For first-time mothers, the evidence is more nuanced — home birth carries a slightly higher risk of requiring emergency transfer to hospital. Discuss your specific situation with your midwife.

Safe Sleep Setup at Home

Before the baby arrives, set up the sleep environment using guidance from the Lullaby Trust and the American Academy of Pediatrics (AAP). The baby should sleep on a flat, firm, uninclined surface, on their back, in a clear sleep space — no pillows, duvets, bumpers, or soft toys in the sleeping area. Room-sharing (but not bed-sharing) is recommended for at least the first six months.

Warning Signs Requiring Urgent Assessment

Signs of Pre-Eclampsia

Pre-eclampsia is a serious condition characterised by high blood pressure and organ involvement. Warning signs include: sudden or severe headache, visual disturbances (blurred vision, flashing lights, or spots), severe upper abdominal or right-sided pain, significant swelling of the face, hands, or feet that comes on suddenly, and feeling generally unwell. If you experience any of these, contact your maternity unit or go to hospital immediately — do not wait for a routine appointment.

Reduced Fetal Movement

Fetal movement is a sign of fetal wellbeing. Most pregnant women are aware of regular patterns of movement from around 18–24 weeks. In the third trimester, the pattern and strength of movements matters.

It is a myth that movement slows down towards the end of pregnancy because the baby has less room. If you notice a reduction in the frequency, strength, or pattern of your baby's movements — at any point in the third trimester — contact your maternity unit. Do not wait until the next day. Do not try to stimulate movement by drinking cold water or lying down; contact your maternity unit instead. Reduced fetal movement can be a sign of fetal compromise.

The NHS advises that there is no set number of movements that is normal — what matters is whether the movement pattern has changed for you. If in doubt, contact your maternity unit; they will always prefer that you call.

Signs of Placental Abruption

Placental abruption — where the placenta separates from the uterine wall before delivery — causes sudden, severe abdominal pain, which may be accompanied by vaginal bleeding (though the bleeding can be concealed behind the placenta). It is a medical emergency. Call emergency services if you experience sudden severe abdominal pain, particularly if accompanied by a rigid abdomen or heavy bleeding.

Signs of Preterm Labour

Before 37 weeks, regular contractions, pelvic pressure, low backache, or a change in vaginal discharge (particularly a blood-tinged mucus plug or a gush of fluid) may indicate preterm labour. Contact your maternity unit immediately. Preterm labour does not always progress quickly, and there may be interventions available to delay delivery and give steroids to mature the baby's lungs if delivered early.

Overdue and Induction

Around 40–42% of pregnancies go beyond 40 weeks. Most guidelines offer induction of labour between 41 and 42 weeks. The NHS typically offers induction at 41 weeks and recommends it by 42 weeks, when the risk to the baby begins to increase due to placental aging.

Induction can begin with membrane sweeping (described above), followed if necessary by a prostaglandin gel or pessary inserted into the vagina to ripen the cervix, and then an artificial rupture of membranes and an oxytocin drip if needed. Induced labour may feel more intense than spontaneous labour and the epidural request rate is higher — this is worth knowing in advance.

Frequently Asked Questions

When should I pack my hospital bag?

The NHS and most midwives recommend packing your hospital bag by 36 weeks. If you have had a previous preterm birth or have any risk factors for early delivery, aim to have it ready by 34 weeks.

What does a baby's movements feel like late in pregnancy?

By the third trimester, most women feel a mix of kicks, jabs, rolls, and stretches. The sensation often becomes stronger as the baby grows. The character of movement may change — large rolls become less frequent as space reduces, but jabs and kicks should remain regular and strong. Any sudden reduction in the usual pattern warrants a call to your maternity unit.

How do I know if my waters have broken?

A gush of fluid from the vagina, or a persistent trickle you cannot control, may indicate that your membranes have ruptured. Put on a sanitary pad and contact your maternity unit. The fluid should be clear or pale pink — if it is green, brown, or foul-smelling, this is more urgent. Even if you are not having contractions, contact your maternity unit promptly.

Is it normal to feel anxious about labour in the third trimester?

Yes. Anxiety about labour and birth is extremely common and does not reflect a problem with your coping ability. Discuss any fears with your midwife — many maternity units offer birth debriefs for women who had a difficult previous birth, and some offer referral to a specialist perinatal mental health service for significant anxiety. Antenatal education classes, hypnobirthing, and knowing your options all help reduce anxiety.

Can I still sleep on my back in the third trimester?

The NHS advises pregnant women to go to sleep on their side from 28 weeks. Research published in the BMJ has shown an association between going to sleep on your back in the third trimester and an increased risk of stillbirth. If you wake up on your back, do not be alarmed — simply turn onto your side and go back to sleep. Placing a pillow behind you can help prevent rolling onto your back.

What is engagement and does it mean labour is imminent?

Engagement means the baby's head has descended into the upper pelvis. In first pregnancies, this often happens around 36 weeks. In subsequent pregnancies, it often does not happen until active labour has begun. Engagement does not mean labour is imminent — it simply means the head is in the right position.

Key Takeaways

• The third trimester spans weeks 28–40; week 28 marks legal viability, week 32 brings significantly improved NICU survival rates, and week 37 marks term
• Baby is gaining weight rapidly, lungs are maturing, and the immune system is receiving maternal antibodies via the placenta
• Braxton Hicks contractions, back pain, pelvic girdle pain, heartburn, swelling, itching, and sleeplessness are common — most are normal but some overlap with warning signs that need assessment
• Antenatal appointments at 28, 34, 36, 38, and 40 weeks check blood pressure, urine, fundal height, and baby position; GBS testing is offered at 35–37 weeks in the US
• Prepare a birth plan, pack your hospital bag by 36 weeks, and know your pain relief and birth setting options in advance
• Contact your maternity unit immediately for: reduced or changed fetal movement, signs of pre-eclampsia (severe headache, visual disturbances, upper abdominal pain), sudden severe abdominal pain, heavy vaginal bleeding, or any contractions before 37 weeks
• The NHS recommends sleeping on your side from 28 weeks — if you wake on your back, turn over and do not worry
• Induction is typically offered between 41 and 42 weeks; the NHS recommends it by 42 weeks when placental risk increases

📋 SOURCES & FACT-CHECKING

This article is compiled and verified against these authoritative sources: - CDC (Centers for Disease Control & Prevention) - WHO (World Health Organization) - ACOG (American College of Obstetricians and Gynecologists) - NHS (National Health Service) - AAP (American Academy of Pediatrics)

Last verified: June 2026

Educational content only. Always consult your pediatrician for medical decisions.

Related Articles

• Pregnancy Symptoms By Week
• When To Go To Hospital Labor
• Birth Plan Template
• Labor Positions Guide