Pregnancy week 27 is an important milestone because it is the final week of the second trimester under the trimester definition used by the American College of Obstetricians and Gynecologists (ACOG).

The fetus is growing quickly, the brain is undergoing rapid development, the nervous system can control more body functions, the eyelids can open and close, and the lungs continue producing surfactant.

At the same time, the pregnant person’s body is preparing for the third trimester. The growing uterus can contribute to constipation, bloating, heartburn, snoring, sleep difficulty, backache and stronger awareness of fetal movement.

Week 27 is also an important prenatal-testing week because it is near the end of the routine 24–28 week gestational-diabetes screening window.

Quick answer: At 27 weeks pregnant, the fetus is approximately 36.6 cm from head to heel according to NHS guidance—roughly the size of a cauliflower. The brain is growing rapidly, the nervous system is increasingly able to control body functions, eyelids can open and close, surfactant production continues, and more fat is accumulating beneath the skin.

Is 27 Weeks Pregnant Still the Second Trimester?

Yes.

ACOG defines the trimesters as:

• first trimester: through 13 weeks 6 days;
• second trimester: 14 weeks 0 days through 27 weeks 6 days;
• third trimester: beginning at 28 weeks 0 days.

That means pregnancy week 27 is the last week of the second trimester.

Week 28 begins the third trimester.

How Big Is the Baby at 27 Weeks?

The NHS estimates the fetus at around 36.6 cm from head to heel.

That is approximately the size of a cauliflower.

These measurements are averages rather than targets.

Individual fetal size varies because of factors such as:

• genetics;
• exact gestational age;
• natural biological variation;
• measurement technique.

A single size estimate cannot diagnose whether fetal growth is normal.

What Is Developing at 27 Weeks Pregnant?

MedlinePlus groups weeks 27–30 together as an important developmental phase.

During this period:

• the brain grows rapidly;
• the nervous system becomes developed enough to control some body functions;
• the eyelids can open and close;
• the respiratory system remains immature but produces surfactant.

ACOG also describes weeks 25–28 as a stage when:

• the lungs are formed but not yet ready to function independently;
• loud sounds can cause a startle response;
• eyelids open and close;
• surfactant production begins;
• the nervous system continues developing;
• skin becomes smoother as more fat accumulates.

Is the Baby’s Brain Growing Rapidly at 27 Weeks?

Yes.

Rapid brain development is one of the most important features of this stage.

MedlinePlus specifically states that during weeks 27–30 the fetal brain grows rapidly.

Brain development involves increasing complexity of:

• nerve connections;
• movement control;
• sensory processing;
• sleep regulation;
• reflex pathways.

The brain is still far from fully mature and continues developing through the third trimester and after birth.

What Does Nervous-System Control Mean?

The nervous system is becoming able to coordinate more body functions.

MedlinePlus notes that by weeks 27–30 it is developed enough to control some body functions.

This increasing control contributes to:

• stronger movements;
• reflexes;
• eye opening and closing;
• responses to sound;
• more organized sleep and activity cycles.

Can the Baby Open and Close Its Eyes?

Yes.

Both ACOG and MedlinePlus describe eyelid opening and closing during this developmental period.

However, opening the eyes does not mean vision is fully developed.

The visual system still needs further maturation of:

• the retina;
• optic nerves;
• brain pathways responsible for processing visual information.

Can the Baby See at 27 Weeks?

Vision remains immature.

The eyes can open and close, but the fetus does not see the outside world as a newborn does.

Light reaching the uterus is limited and filtered through:

• clothing;
• abdominal tissue;
• uterine tissue.

Visual responses become more developed later in pregnancy.

Is the Baby Still Responding to Sound?

Yes.

ACOG notes that during weeks 25–28 familiar sounds, including the pregnant person’s voice, may produce movement, while loud sounds may cause a startle response.

This reflects increasing maturity of:

• hearing pathways;
• brain processing;
• nervous-system reflexes.

Can the Baby Recognize Your Voice?

The fetus can become familiar with recurring sounds.

ACOG specifically notes movement responses to familiar sounds such as the pregnant person’s voice during this stage.

This should not be interpreted as understanding speech.

The fetus is responding to sound patterns rather than language meaning.

Should You Play Music to the Baby?

Normal music and conversation are fine.

There is no need to:

• play loud sounds;
• place headphones on the abdomen;
• use special “brain development” audio programs.

The auditory system develops naturally through ordinary sound exposure.

Are the Lungs Developed at 27 Weeks?

The lungs are substantially developed structurally but remain immature.

ACOG states that during weeks 25–28 the lungs are formed but not yet ready to function outside the uterus.

The fetus continues depending on the placenta for oxygen.

Is Surfactant Being Produced?

Yes.

Both ACOG and MedlinePlus identify surfactant production during this developmental period.

Surfactant helps prevent the tiny lung air sacs from collapsing after birth.

Production increases as pregnancy progresses.

Why Is Surfactant Important?

After birth, lung air sacs need to remain open between breaths.

Surfactant reduces surface tension inside these sacs.

Without enough surfactant, breathing can be difficult.

At 27 weeks, surfactant production is underway, but lung maturation still has a long way to go.

Does the Baby Practice Breathing?

Yes.

Breathing-like fetal movements continue.

These movements exercise:

• the diaphragm;
• chest muscles;
• developing lungs.

However, the fetus does not breathe air inside the uterus.

Oxygen is supplied through the placenta and umbilical cord.

Is the Baby Gaining More Fat?

Yes.

ACOG specifically notes that at 27 weeks more fat is being added to help keep the fetus warm.

Fat accumulation helps:

• smooth wrinkled skin;
• provide energy reserves;
• support temperature control after birth.

A large amount of fetal weight gain still occurs during the third trimester.

Is the Skin Becoming Smoother?

Yes.

Earlier in the second trimester, the fetal skin was thin and wrinkled.

As fat accumulates underneath it, the skin gradually becomes smoother.

The NHS similarly notes that folds in the skin are beginning to fill out as the fetus becomes plumper.

Is Vernix Still Protecting the Skin?

Yes.

ACOG notes that vernix has developed during this stage and acts as a waterproof barrier protecting fetal skin.

Vernix is the creamy protective substance coating the fetus.

It helps protect the skin while surrounded by amniotic fluid.

Is the Baby Moving Strongly at 27 Weeks?

Movement usually feels much stronger than it did several weeks earlier.

You may feel:

• kicks;
• rolls;
• turns;
• stretches;
• pushing;
• rhythmic hiccups.

The fetus is larger and its muscles and nervous system are more developed.

Should You Feel the Baby Move Every Day?

Many people notice fetal activity regularly by 27 weeks.

Movement patterns differ between pregnancies.

What matters most is becoming familiar with your baby’s usual pattern rather than comparing movement with another pregnancy.

If your baby’s movements become noticeably reduced or stop, contact your maternity healthcare service.

Should You Count Kicks at 27 Weeks?

Movement-monitoring advice varies between healthcare systems.

Some clinicians introduce formal counting later, while others emphasize recognizing the baby’s usual pattern.

Do not rely on a universal internet number.

Follow your maternity team’s guidance.

What If Movement Seems Reduced?

A meaningful reduction in movement should be taken seriously.

Decreased fetal movement is one of the reasons ACOG says additional fetal wellbeing testing may sometimes be considered.

Contact your maternity healthcare provider rather than trying to stimulate movement with:

• sugar;
• cold drinks;
• loud music;
• home Doppler devices.

Is the Baby Sleeping?

Yes.

Fetal sleep and waking patterns continue developing.

Periods of lower activity may simply reflect sleep.

However, sleep should not be assumed as the explanation for a concerning reduction in your baby’s normal movement pattern.

What Is Happening in Your Body at 27 Weeks?

The NHS describes week 27 as a period when you may notice:

• weight gain;
• bloating;
• constipation;
• tiredness;
• sleep problems;
• snoring.

These changes are related partly to the growing uterus and pregnancy hormones.

Why Are Bloating and Constipation Common?

The NHS explains that the growing fetus can place more pressure on the digestive system, while the hormone progesterone can slow digestion.

This can contribute to:

• constipation;
• bloating;
• fullness;
• gas.

What Can Help Constipation?

General measures include:

• drinking enough water;
• choosing high-fiber foods;
• eating fruit and vegetables;
• remaining appropriately active.

The NHS specifically recommends higher-fiber choices such as whole-grain foods.

If constipation is severe, ask a healthcare professional about pregnancy-safe treatments.

Is Heartburn Normal at 27 Weeks?

Yes.

As the uterus expands, pressure on the stomach increases.

Pregnancy hormones also relax digestive muscles.

Helpful measures can include:

• smaller meals;
• avoiding foods that trigger symptoms;
• staying upright after eating;
• avoiding large meals before bed.

Ask a healthcare professional about appropriate treatment if symptoms are persistent.

Why Might You Snore More During Pregnancy?

The NHS notes that snoring can become more common because pregnancy may make the nasal passages swollen and blocked.

This can increase nighttime breathing noise.

Snoring itself can be common, but severe sleep-disordered breathing symptoms should be discussed with a clinician.

When Should Snoring Be Discussed With a Doctor?

Speak with a healthcare professional if snoring is associated with:

• gasping during sleep;
• repeated breathing pauses reported by someone else;
• extreme daytime sleepiness;
• severe morning headaches;
• other concerning symptoms.

These may deserve further assessment.

Is Tiredness Returning at 27 Weeks?

It can.

The NHS notes that tiredness may increase again around week 27.

Possible contributing factors include:

• carrying additional weight;
• sleep disruption;
• discomfort;
• anemia;
• stress.

Mention significant fatigue at your prenatal appointments.

What Symptoms Are Common at 27 Weeks?

Possible symptoms include:

• tiredness;
• sleep problems;
• stretch marks;
• bleeding or swollen gums;
• round-ligament pain;
• hemorrhoids;
• headaches;
• backache;
• nosebleeds;
• indigestion;
• heartburn;
• bloating;
• constipation;
• leg cramps;
• feeling hot;
• dizziness;
• swollen hands and feet;
• urinary infections;
• vaginal infections;
• facial pigmentation changes;
• oily skin;
• thicker hair.

The NHS lists these among possible late-second-trimester symptoms.

Is Back Pain Normal?

Mild backache is common as:

• the uterus grows;
• your center of gravity shifts;
• posture changes;
• ligaments become more flexible.

Helpful measures may include:

• supportive footwear;
• appropriate activity;
• careful lifting;
• avoiding prolonged awkward positions.

Severe or persistent pain deserves assessment.

Is Round Ligament Pain Still Possible?

Yes.

The NHS continues to list side pain from the expanding uterus among possible symptoms.

Round-ligament pain may feel like:

• pulling;
• stretching;
• brief sharp discomfort.

Severe or persistent abdominal pain should not be self-diagnosed as ligament pain.

Are Hemorrhoids Common?

Yes.

Constipation and pressure from the growing uterus can contribute to hemorrhoids.

General measures that may help include:

• avoiding constipation;
• not straining;
• drinking enough water;
• eating fiber-rich foods.

Ask a healthcare professional about pregnancy-safe treatment if symptoms are troublesome.

Are Leg Cramps Still Common?

Yes.

Leg cramps can continue during late second trimester.

Gentle stretching may help.

Seek urgent assessment if one leg becomes:

• swollen;
• red;
• warm;
• persistently painful.

These symptoms can have causes other than ordinary muscle cramp.

Is Swelling Normal?

Mild swelling can occur.

However, sudden or severe swelling—especially when accompanied by:

• severe headache;
• visual changes;
• pain below the ribs;
• feeling seriously unwell;

requires medical assessment.

These symptoms can be associated with pregnancy complications including pre-eclampsia.

Is Vaginal Discharge Normal?

White or milky pregnancy discharge may be normal.

Seek advice if discharge becomes:

• green or yellow;
• foul smelling;
• itchy;
• painful;
• associated with fever.

A gush or continuing watery leakage requires prompt assessment.

What About Bleeding?

Any pregnancy bleeding should be medically assessed.

Seek urgent care for:

• heavy bleeding;
• severe pain;
• regular contractions;
• fainting;
• fluid leakage.

Can Braxton Hicks Happen at 27 Weeks?

Yes.

Occasional irregular uterine tightening can occur.

Braxton Hicks contractions are generally:

• irregular;
• brief;
• not progressively stronger.

Regular or painful contractions at 27 weeks require prompt assessment because preterm labor needs to be considered.

What Is the Glucose Screening Deadline?

Week 27 is near the end of the routine gestational-diabetes screening period.

ACOG states that glucose screening usually takes place between 24 and 28 weeks.

If your clinician recommended the test and it has not yet been completed, ask about scheduling it.

What Is Gestational Diabetes?

Gestational diabetes is diabetes diagnosed during pregnancy.

Pregnancy hormones can make insulin less effective, causing blood glucose to rise.

It may occur without obvious symptoms.

That is why screening is routinely used.

What Happens During Glucose Screening?

ACOG describes a common screening method:

• drink a glucose-containing solution;
• wait about one hour;
• have a blood sample collected.

If the result is elevated, a longer glucose test may be needed to confirm the diagnosis.

Does a High Screening Result Mean You Have Gestational Diabetes?

Not automatically.

The initial test is a screening test.

An elevated result generally means additional testing is required.

Do not diagnose yourself from one number.

What Happens If Gestational Diabetes Is Diagnosed?

ACOG notes that management can include:

• healthy eating;
• regular activity;
• glucose monitoring;
• medication when necessary.

More frequent prenatal monitoring may also be recommended.

What About Anemia?

A complete blood count can identify anemia by measuring blood-cell levels.

ACOG explains that red blood cell measurements help determine whether anemia is present.

Later-pregnancy blood testing schedules vary.

Symptoms such as fatigue and breathlessness cannot diagnose anemia on their own.

Is Iron Still Important?

Yes.

Iron supports:

• maternal red blood cells;
• oxygen transport;
• fetal growth.

Dietary iron sources can include:

• meat;
• beans;
• lentils;
• fortified cereals;
• leafy green vegetables.

Some people require supplements based on blood-test results.

What If You Are Rh Negative?

Your blood type and Rh status are usually identified earlier in pregnancy.

ACOG states that Rh-negative patients may have antibody testing repeated at around 28 weeks and may be given Rh immunoglobulin when indicated.

Week 27 is therefore a useful time to know whether this applies to you.

What Is Rh Immunoglobulin?

Rh immunoglobulin, often abbreviated RhIg, is medication used to help prevent an Rh-negative pregnant person’s immune system from developing antibodies against Rh-positive fetal blood cells.

ACOG notes that it is commonly given around 28 weeks when appropriate.

It is only relevant to specific pregnancies.

Does Every Pregnant Person Need RhIg?

No.

It depends on:

• the pregnant person’s Rh status;
• whether Rh antibodies are already present;
• individual pregnancy circumstances.

Your healthcare team can determine whether it is appropriate.

Is It Time to Think About Sleep Position?

Yes.

The NHS notes that after 28 weeks, going to sleep on either side is preferable to going to sleep on the back.

Week 27 is therefore a good time to start becoming comfortable with side sleeping.

What If You Wake Up on Your Back?

Do not panic.

The NHS advises simply rolling back onto your side if you wake on your back.

The emphasis is on the position you go to sleep in rather than becoming anxious about natural movement during sleep.

Which Side Should You Sleep On?

The NHS guidance cited on the week-27 page says either side is preferable to sleeping on the back after week 28.

Comfort may improve with:

• a pillow under the bump;
• a pillow between the knees;
• knees slightly bent.

Why Does Sleep Position Matter More Later?

As pregnancy advances, the uterus becomes large enough to place pressure on major blood vessels when lying flat on the back.

This is one reason side sleeping becomes increasingly relevant in the third trimester.

Is Flying Still Possible at 27 Weeks?

Often, yes, in an uncomplicated pregnancy.

However, the NHS notes that airline documentation requirements may become more common after this stage.

Airlines set their own policies.

Check:

• airline rules;
• insurance;
• access to maternity care;
• your clinician’s advice.

Do You Need a Fit-to-Fly Letter?

This depends on:

• airline;
• gestational age;
• whether the pregnancy is uncomplicated;
• destination.

The NHS notes that some airlines request documentation after approximately week 28.

Always check the specific airline before travel.

Can You Exercise at 27 Weeks?

Many people with uncomplicated pregnancies can remain physically active.

The NHS recommends approximately 150 minutes of exercise per week during pregnancy.

Suitable activity may include:

• walking;
• swimming;
• prenatal exercise;
• pregnancy-appropriate strength work.

Adjust intensity and balance demands as the abdomen grows.

Are Pelvic Floor Exercises Important?

Yes.

The NHS encourages pelvic-floor exercises during pregnancy to help reduce urine leakage when:

• coughing;
• sneezing;
• laughing.

The pelvic floor supports the:

• bladder;
• uterus;
• bowel.

Should You Start Eating Extra Calories Now?

Under NHS guidance, not yet.

The NHS states that additional calories are not required until the third trimester, which begins at week 28.

Continue focusing on:

• nutrient quality;
• balanced meals;
• adequate protein;
• iron;
• calcium;
• vegetables;
• fruit;
• whole grains.

Is Vitamin D Important?

Yes.

Vitamin D supports healthy bones and muscles.

The NHS advises a daily 10 microgram supplement for some pregnant people depending on season and individual circumstances in the UK.

Supplement recommendations vary by country.

Is Whooping Cough Vaccination Still Relevant?

Yes, depending on your healthcare system.

The NHS states that whooping cough vaccination can be given between 16 and 32 weeks.

Follow the pregnancy vaccination schedule used in your country.

Is It Time for Antenatal Classes?

Yes.

Week 27 is a good time to be attending or arranging classes.

They may cover:

• labor;
• birth positions;
• pain relief;
• breastfeeding;
• newborn care;
• partner support.

The NHS recommends asking your midwife or doctor about available classes.

Should You Think About Where to Give Birth?

Yes.

The NHS specifically identifies week 27 as a useful time to think about preferred birth location.

Available choices depend on:

• local services;
• pregnancy risk;
• medical history;
• personal preference.

Your maternity team can explain appropriate options.

Should You Finish a Birth Plan?

You can begin making one, but it does not have to be final.

A birth plan may include preferences about:

• labor support;
• pain relief;
• mobility;
• feeding;
• newborn care.

Birth plans should remain flexible because medical circumstances can change.

What About Postpartum Contraception?

Pregnancy is a reasonable time to start discussing contraception after birth.

The NHS highlights this because fertility can return sooner than many people expect.

There is no need to make a final choice immediately.

Is Mental Health Important at Week 27?

Yes.

Pregnancy-related anxiety and low mood deserve professional attention.

Speak with a healthcare professional if you experience:

• persistent sadness;
• persistent anxiety;
• inability to sleep because of worry;
• difficulty functioning normally;
• feeling unable to cope.

Mental health is part of routine maternity care.

Is Sex Safe at 27 Weeks?

For most uncomplicated pregnancies, sexual activity remains possible.

Seek personalized advice if you have:

• bleeding;
• fluid leakage;
• placenta-related complications;
• cervical problems;
• regular painful contractions;
• medical advice to avoid intercourse.

When Should You Seek Medical Help at 27 Weeks?

Seek urgent medical assessment for:

• heavy vaginal bleeding;
• regular painful contractions;
• significant or persistent fluid leakage;
• severe abdominal or pelvic pain;
• a meaningful reduction or stopping of fetal movement;
• severe headache with visual changes;
• sudden significant swelling;
• severe pain below the ribs;
• fainting;
• sudden or severe breathlessness;
• chest pain;
• high fever;
• severe one-sided leg pain or swelling.

At 27 weeks, symptoms of preterm labor, pre-eclampsia or reduced fetal movement require professional assessment rather than online self-diagnosis.

Pregnancy Week 27 FAQs

How big is the baby at 27 weeks?

The NHS estimates the fetus at around 36.6 cm from head to heel, approximately the size of a cauliflower.

Is week 27 still the second trimester?

Yes. ACOG defines the second trimester as ending at 27 weeks 6 days.

When does the third trimester start?

The third trimester begins at 28 weeks 0 days under ACOG’s definition.

What is developing at 27 weeks?

The brain is growing rapidly, the nervous system controls more body functions, the eyelids open and close, surfactant production continues and more fat is being added.

Is the baby’s brain growing rapidly?

Yes. MedlinePlus specifically identifies rapid brain growth during weeks 27–30.

Are the lungs mature?

No. Surfactant is being produced, but the respiratory system remains immature.

Can the baby open its eyes?

Yes. Eyelids can open and close during this stage.

Is the baby gaining more fat?

Yes. ACOG specifically notes increased fat accumulation at week 27.

Should you feel the baby move every day?

Many people feel regular fetal activity by this stage. If movement becomes significantly reduced from your baby’s usual pattern, contact your maternity provider.

Is glucose testing still done at 27 weeks?

Yes. Week 27 is within the usual 24–28 week gestational-diabetes screening window.

What if I am Rh negative?

ACOG notes that Rh-negative patients may have antibody testing and Rh immunoglobulin management around 28 weeks, depending on their situation.

Is constipation normal at 27 weeks?

Yes. The NHS notes that progesterone and pressure from the growing uterus can contribute to constipation and bloating.

Is snoring normal during pregnancy?

It can become more common because nasal tissues may swell and become blocked.

Should you sleep on your side?

From week 28 onward, NHS guidance recommends going to sleep on either side rather than on the back. Week 27 is a good time to get comfortable with side sleeping.

Is week 27 the last week of the second trimester?

Yes. Week 28 begins the third trimester.

What Comes Next?

Pregnancy Week 28 marks the beginning of the third trimester.

From week 28 onward, fetal growth increasingly focuses on:

• weight gain;
• brain and nervous-system maturation;
• lung development;
• stronger movement;
• increasing fat stores.

ACOG describes the third trimester as the stage when fetal weight increases and organs mature in preparation for functioning after birth.

Week 28 is also particularly relevant for:

• completing gestational-diabetes screening if still outstanding;
• Rh-negative pregnancy care where appropriate;
• third-trimester prenatal planning;
• sleep-position guidance;
• closer awareness of fetal movement.

Previous: Pregnancy Week 26
Next: Pregnancy Week 28
Tool: Pregnancy Due Date Calculator

Medical References

This article is based on current educational information from established medical and public-health organizations, including:

• NHS — 27 Weeks Pregnant
• MedlinePlus — Fetal Development
• American College of Obstetricians and Gynecologists (ACOG) — How Your Fetus Grows During Pregnancy
• ACOG — Changes During Pregnancy
• ACOG — Routine Tests During Pregnancy
• ACOG — Gestational Diabetes
• ACOG — The Rh Factor: How It Can Affect Your Pregnancy

Editorial & Medical Information

Last content review: October 2026

This page provides general educational pregnancy information only. It does not diagnose preterm labor, pre-eclampsia, gestational diabetes, anemia or fetal wellbeing; interpret laboratory results; recommend medications; or replace individualized prenatal care.

Pregnancy symptoms, fetal movement, test schedules and medical needs vary. Contact a qualified healthcare professional for personal concerns about fetal movement, contractions, bleeding, fluid leakage, glucose testing, Rh status, severe swelling, headache or other symptoms.

Conclusion

Pregnancy week 27 closes the second trimester and introduces a period of particularly rapid brain and nervous-system development. MedlinePlus describes weeks 27–30 as a stage when the fetal brain grows rapidly, the nervous system gains control over some body functions, eyelids open and close, and the immature respiratory system continues producing surfactant.

The NHS estimates the fetus at around 36.6 cm from head to heel, while ACOG specifically notes that more fat is being deposited at week 27 to help prepare the fetus for temperature regulation after birth.

For the pregnant person, digestive pressure and progesterone can contribute to bloating and constipation, while tiredness, snoring, heartburn, backache and sleep problems may become more prominent as the third trimester approaches.

Week 27 is also an important practical checkpoint: routine gestational-diabetes screening is normally performed from 24 to 28 weeks, while Rh-negative patients may need specific testing or Rh immunoglobulin management around week 28.

Continue regular prenatal care and become familiar with your baby’s usual movement pattern. Heavy bleeding, painful regular contractions, ongoing fluid leakage, severe headache with vision changes, major swelling or a meaningful reduction in fetal movement requires prompt professional medical assessment.