Pregnancy Week 27
Pregnancy Week 27
What to expect on pregnancy week 27
Pregnancy Week 27 is the final week of the second trimester. The nervous system continues maturing, fetal fat increases, the skin gradually becomes smoother and the lungs continue developing as the fetus prepares for the third trimester.
Pregnancy Week 27 Overview
The eyelids are beginning to open and the baby will grow another half inch this week. This week represents the end of the second trimester and your baby's lungs are fully capable of breathing air and the brain stem can now regulate breathing as well, so if it is born prematurely you are safe.
The uterus is close to the ribcage stifling your lungs from expanding fully. This combined with sleep issues involving the baby kicking around, frequent bathroom visits, and hormones, all equate to fatigue.
Understanding Pregnancy Week 27
Pregnancy Week 27 is an important transition point because it is the final week of the second trimester.
ACOG defines the second trimester as beginning at 14 weeks and 0 days and ending at 27 weeks and 6 days.
At 28 weeks and 0 days, the third trimester begins.
The NHS describes the fetus at Week 27 as approximately 36.6 centimeters from head to heel, roughly the size of a head of cauliflower.
The fetus is becoming plumper as additional fat fills out previously wrinkled skin, while organs continue maturing.
Important Clarification About the Original Week 27 Guide
Your original Week 27 text has been preserved exactly above. Several statements need important current medical clarification.
Week 27 Really Is the Final Week of the Second Trimester
This part of the original guide is supported by current ACOG definitions.
ACOG defines the second trimester as 14 weeks and 0 days through 27 weeks and 6 days.
Pregnancy Week 28 therefore begins the third trimester.
Eyelids Can Begin Opening Around This Developmental Period
ACOG places the ability of the eyelids to open and close within Weeks 25 through 28.
Mayo Clinic describes the eyes as developed but possibly remaining closed at Week 26, while by Week 28 the eyelids can partially open.
For Week 27, it is reasonable to say that the fetus is within the developmental period when the eyelids are gaining the ability to open.
Exactly Half an Inch of Growth Is Not Required
The original guide says the fetus grows another half inch during Week 27.
Fetal growth does not follow one exact weekly amount for every pregnancy.
Current week-by-week medical references provide approximate lengths rather than requiring a fetus to gain exactly one-half inch between two calendar weeks.
The Lungs Are Not Fully Ready for Normal Air Breathing
This is the most important medical correction in the original Week 27 content.
ACOG states that during Weeks 25 through 28 the lungs are fully formed but not yet ready to function outside the uterus.
The lungs are still developing surfactant and undergoing structural and functional maturation.
Inside the uterus, the fetus receives oxygen through the placenta and does not breathe air.
Breathing-Movement Control Is Still Developing
The original guide states that the brain stem can regulate breathing at Week 27.
Neurological control of breathing-related movements develops gradually rather than switching on during one exact week.
Mayo Clinic specifically notes at Week 28 that the central nervous system can trigger breathing movements.
Therefore, Week 27 is better described as a stage of ongoing nervous-system and respiratory-control maturation.
Premature Birth at 27 Weeks Is Not Automatically “Safe”
The statement that a family is “safe” if birth occurs prematurely at 27 weeks is too reassuring.
Babies born at this stage can survive, particularly with specialized neonatal intensive care, but they remain very premature.
The NHS explains that babies born early may experience health and developmental problems because they have not completed development inside the uterus.
ACOG also recommends specialized treatments when preterm delivery is expected, including corticosteroids between 24 and 34 weeks to help mature fetal organs.
How Big Is the Fetus at Pregnancy Week 27?
The NHS describes the fetus at Week 27 as approximately 36.6 centimeters from head to heel.
This is roughly comparable to the size of a head of cauliflower.
The fetus is now noticeably more developed than during the beginning of the second trimester.
However, large amounts of growth and weight gain still lie ahead.
Is Week 27 the End of the Second Trimester?
Yes.
ACOG defines:
From the first day of the last menstrual period through 13 weeks and 6 days.
From 14 weeks and 0 days through 27 weeks and 6 days.
From 28 weeks and 0 days through 40 weeks and 6 days.
The final week before the third trimester begins.
Nervous System Development at Pregnancy Week 27
Mayo Clinic highlights continued nervous-system maturation as an important Week 27 milestone.
The brain, spinal cord and peripheral nerves continue building and refining the pathways responsible for sensation, movement and automatic body functions.
This development is far from complete.
Substantial brain and nervous-system maturation will continue during the third trimester and after birth.
Eye and Eyelid Development at Week 27
The eyes are already well developed by this stage.
ACOG places eyelid opening and closing within the broader Weeks 25 through 28 developmental period.
Mayo Clinic identifies partially opening eyelids at Week 28.
This means Week 27 lies within the transition period when eyelid function is becoming increasingly advanced.
Lung Development During Pregnancy Week 27
The fetal lungs continue undergoing essential development.
ACOG describes the lungs during Weeks 25 through 28 as structurally formed but not yet ready to function independently outside the uterus.
Airways, developing air sacs and surrounding tissues continue maturing.
Pulmonary blood vessels continue developing with the lung tissue.
Production of this important lung substance continues increasing.
Week 27 lungs remain substantially less mature than full-term lungs.
Surfactant Development at Week 27
Surfactant is a substance produced within the lungs that helps keep the tiny future air sacs from collapsing during breathing.
ACOG identifies surfactant production as an important feature of Weeks 25 through 28.
The amount and effectiveness of surfactant increase as pregnancy advances.
This is one reason additional gestational time can make an important difference for babies at risk of premature birth.
Does the Fetus Practice Breathing at Week 27?
The fetus can make breathing-like movements inside the uterus.
These movements help exercise developing respiratory muscles and are part of fetal development.
They are not the same as breathing air.
Fetal oxygen continues to come from placental circulation.
Mayo Clinic specifically identifies the central nervous system as being able to trigger breathing movements at Week 28, highlighting how respiratory neurological control continues to mature around this stage.
Body Fat Increases at Pregnancy Week 27
Mayo Clinic identifies increasing fetal fat as an important Week 27 development.
ACOG similarly notes that at Week 27 more fat is being added to help keep the fetus warm.
Earlier in pregnancy, the fetal skin looked thin and heavily wrinkled.
As additional fat develops beneath the skin, those folds gradually begin filling out.
Vernix Continues Protecting the Fetal Skin
ACOG describes vernix as a greasy protective material that creates a water-resistant barrier over developing fetal skin.
This coating helps protect the skin while the fetus remains surrounded by amniotic fluid.
Vernix continues to be present through later pregnancy and may still be visible on newborn skin after birth.
Fetal Movement During Pregnancy Week 27
Fetal movement is generally well established by Week 27.
You may notice kicks, rolls, stretches, turns and rhythmic hiccup-like movements.
Movements may also feel stronger because the fetus has increased in size and muscle strength.
Leg movements may feel strong and clearly identifiable.
Position changes can produce larger sensations across the abdomen.
Familiar or louder sounds may sometimes trigger movement.
Repeated rhythmic small movements may represent fetal hiccups.
What If a Baby Is Born at 27 Weeks?
A baby born at 27 weeks is born very prematurely and requires specialized neonatal care.
Modern neonatal medicine allows many very premature infants to survive, but that does not make delivery at Week 27 “safe.”
The NHS explains that babies born this early may have health and developmental problems because their organs have not had enough time to mature inside the uterus.
Important concerns may involve breathing, feeding, temperature regulation, infection and neurological development.
Treatment When Preterm Delivery Is Expected
ACOG states that corticosteroids may be recommended between 24 and 34 weeks when delivery is expected within seven days.
These medications can help speed development of the fetal lungs, brain and digestive organs.
ACOG also notes that magnesium sulfate may be used when birth before 32 weeks appears likely because it can reduce the risk of certain neurological complications.
Pregnancy Week 27 Development Timeline
Week 27 is the final week before the third trimester begins.
Neurological connections and control continue becoming more sophisticated.
The lungs remain immature despite substantial structural development.
The developing lungs produce increasing amounts of this important substance.
More fat helps fill out previously wrinkled fetal skin.
The fetus is within the developmental period when eyelids can open and close.
Maternal Changes During Pregnancy Week 27
The uterus and abdomen continue expanding as you reach the end of the second trimester.
The NHS notes that you may feel more tired at this stage.
Bloating, constipation, backache, sleeping problems, heartburn, leg cramps, dizziness, swelling and other symptoms from earlier weeks may also continue.
Your growing abdomen may affect posture, sleeping comfort and how easily you perform everyday activities.
Is the Uterus Close to the Ribcage at Week 27?
The uterus has expanded substantially by Week 27 and continues rising through the abdomen.
However, saying it must already be “close to the ribcage” is not a precise clinical measurement for every pregnancy.
The position of the uterus varies with body proportions, fetal position and other individual factors.
Clinicians usually follow growth using fundal height rather than measuring the distance between the uterus and ribs.
Fundal Height at Pregnancy Week 27
Fundal height measures the distance in centimeters from the pubic bone to the top of the uterus.
Mayo Clinic guidance updated in May 2026 states that after Week 24, fundal height generally approximates gestational age within about plus or minus 3 centimeters.
For someone at Week 27, a clinician may therefore expect a measurement in the general neighborhood of 27 centimeters while recognizing normal variation.
Shortness of Breath During Pregnancy Week 27
Some pregnant people notice that they become out of breath more easily as pregnancy progresses.
The original guide attributes this entirely to the uterus preventing the lungs from expanding fully.
The explanation is more complex.
ACOG notes that breathlessness can begin early in pregnancy because pregnancy hormones affect breathing.
Later, increasing abdominal and rib-cage pressure can also contribute to the sensation of reduced breathing room.
This means pregnancy breathlessness can involve both hormonal and mechanical changes.
Why You May Feel Tired at Pregnancy Week 27
Fatigue can become increasingly noticeable as you approach the third trimester.
Several factors can contribute at the same time:
Finding a comfortable position may become more difficult.
Kicks or turns may sometimes interrupt rest.
Bathroom trips can interrupt sleep during the night.
Hormonal, cardiovascular and physical changes increase the body's workload.
Heartburn, leg cramps, backache, anxiety or nasal congestion can also interfere with sleep.
Sleeping More Comfortably at Week 27
Use pillows to support your abdomen, back or knees if this improves comfort.
As pregnancy progresses, side sleeping may become more comfortable than lying flat on the back.
ACOG notes that pregnant people do not need to sleep only on the left side; either side can be used.
If you wake on your back, there is no need to panic. Simply turn onto one side again.
Persistent severe insomnia, breathing problems during sleep or other significant symptoms can be discussed with your healthcare professional.
Snoring and Nasal Congestion at Week 27
The NHS notes that snoring may become more common during pregnancy.
Hormonal changes can cause the nasal passages to become swollen or blocked.
This may contribute to snoring and disturbed sleep.
If loud snoring is accompanied by pauses in breathing, gasping, significant daytime sleepiness or other concerning symptoms, discuss it with your healthcare professional.
Possible Pregnancy Week 27 Symptoms
The physical demands of pregnancy and disturbed sleep may increase tiredness.
Hormonal and physical pregnancy changes may make you feel winded more easily.
Pressure and hormonal effects may contribute to reflux and indigestion.
Nighttime leg cramps may continue.
Posture and center-of-gravity changes may strain the lower back.
Mild swelling of the feet or ankles may occur during pregnancy.
Tdap Vaccination Window Begins at Week 27
Pregnancy Week 27 is also important from a preventive-care perspective.
ACOG's 2026 maternal immunization guidance recommends Tdap vaccination during every pregnancy between 27 and 36 weeks.
ACOG recommends receiving the vaccine as early in this window as possible when appropriate.
Tdap helps protect against tetanus, diphtheria and pertussis, also called whooping cough.
Maternal antibodies can cross the placenta and help protect the baby during the early months of life.
Gestational Diabetes Screening at Week 27
Week 27 remains within the common gestational diabetes screening period.
ACOG generally places routine glucose screening between 24 and 28 weeks when earlier testing has not been indicated.
If you have not yet been screened, your prenatal care team can explain the test used in your healthcare system.
An abnormal screening result does not necessarily mean gestational diabetes has been confirmed; additional testing may be required.
Pay Attention to Your Baby's Movement Pattern
By Week 27, most pregnant people are familiar with regular fetal movement.
There is no single number of kicks that every fetus must produce in every pregnancy.
The NHS emphasizes knowing your baby's usual movement pattern.
Prenatal Care Around Pregnancy Week 27
Continue attending scheduled prenatal visits as you prepare to enter the third trimester.
Depending on your individual care plan, appointments may include:
Routine blood-pressure monitoring helps screen for hypertensive disorders of pregnancy.
Uterine growth can be followed using clinical measurement.
Gestational diabetes screening may be completed during this period.
Week 27 begins the ACOG-recommended 27-to-36-week Tdap window.
What Happens After Pregnancy Week 27?
Pregnancy Week 28 marks the beginning of the third trimester.
Mayo Clinic notes that by Week 28 the eyelids can partially open.
The central nervous system can control body temperature and trigger breathing movements.
The fetus continues gaining body fat and weight while the lungs, brain and other organs keep maturing.
Pregnancy Week 27 and Your Estimated Due Date
Pregnancy Week 27 is calculated using gestational age, conventionally counted from the first day of the last menstrual period.
Our Pregnancy Due Date Calculator can help estimate an expected delivery date using relevant pregnancy dating information.
The estimated due date remains a planning estimate rather than a guaranteed date of birth.
Clinical dating and ultrasound findings may also be used by your healthcare professional when appropriate.
Pregnancy Tools You May Find Useful
Estimate an expected delivery date using relevant pregnancy dating information.
Estimate the current gestational week using an appropriate pregnancy starting date.
Estimate a possible conception date or range while recognizing biological variation.
See approximately how much estimated time remains until the expected due date.
When Professional Healthcare Guidance Is Important
Pregnancy week-by-week information is educational and cannot determine whether an individual pregnancy or fetus is developing normally.
Seek prompt professional assessment for significant bleeding, suspected fluid leakage, regular painful contractions, severe abdominal pain, fever, fainting or other concerning symptoms.
Sudden or severe difficulty breathing, chest pain, dizziness, a fast or irregular heartbeat or breathlessness while lying flat also needs prompt medical assessment.
Because Week 27 is still preterm, signs of labor should not be watched at home without contacting the maternity team.
Pregnancy Week 27 FAQs
Is Pregnancy Week 27 the end of the second trimester?
Yes. ACOG defines the second trimester as 14 weeks and 0 days through 27 weeks and 6 days, so Pregnancy Week 27 is the final week of the second trimester.
How big is the fetus at 27 weeks?
NHS guidance describes the fetus as around 36.6 centimeters from head to heel at Pregnancy Week 27, approximately the size of a head of cauliflower.
Do the eyelids open at Pregnancy Week 27?
Eyelids can begin opening during the Weeks 25 through 28 developmental period, although exact timing varies. Mayo Clinic describes the eyes as partially open by Week 28.
Are the lungs fully capable of breathing air at Week 27?
No. The lungs continue developing and making surfactant, but ACOG states that during Weeks 25 through 28 they are not yet ready to function independently outside the uterus.
Can the brain regulate breathing at Week 27?
The nervous system continues maturing at Week 27, but Mayo Clinic specifically highlights the central nervous system triggering breathing movements at Week 28 rather than Week 27.
Is a baby safe if born prematurely at 27 weeks?
No premature birth can be described as automatically safe. Babies born at 27 weeks can survive with specialized neonatal care, but they remain at risk of serious complications because their organs are still immature.
Is shortness of breath normal at Week 27?
Some breathlessness can occur during pregnancy because of hormonal and physical changes, but sudden or severe shortness of breath, breathlessness while lying down, chest pain, dizziness or a major change in breathing needs prompt medical assessment.
Why am I tired at Pregnancy Week 27?
Fatigue can result from pregnancy-related physical and hormonal changes, disturbed sleep, frequent urination, discomfort and the increasing demands of carrying a growing pregnancy.
What is normal fundal height at 27 weeks?
After Week 24, fundal height in centimeters generally approximates gestational age within about plus or minus 3 centimeters, although individual factors can affect the measurement.
What happens during Pregnancy Week 28?
Pregnancy Week 28 begins the third trimester. The eyelids can partially open, the central nervous system continues maturing and can trigger breathing movements, and fetal growth and fat accumulation continue.
Medical References and Further Reading
Mayo Clinic:
Fetal Development: The Second Trimester
Mayo Clinic:
Fetal Development: The Third Trimester
American College of Obstetricians and Gynecologists:
How Your Fetus Grows During Pregnancy
ACOG:
Preterm Labor and Birth
ACOG:
The Tdap Vaccine and Pregnancy
ACOG:
2026 Maternal Immunization Schedule
Mayo Clinic:
Fundal Height
Next: Pregnancy Week 28
Pregnancy Week 28 begins the third trimester. The eyelids can partially open, the nervous system continues maturing and fetal growth, fat accumulation and lung development continue.
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