Pregnancy Week 31
Pregnancy Week 31
What to expect on pregnancy week 31
Pregnancy Week 31 brings rapid fetal growth and continued organ maturation. The fetus remains active, gains body fat, becomes progressively plumper and continues developing the brain, lungs, nervous system and skills needed after birth.
Pregnancy Week 31 Overview
At Pregnancy Week 31, most major fetal structures have already developed, but pregnancy is far from finished. The fetus now enters an especially important period of rapid weight gain while the brain, lungs, nervous system and other organs continue maturing.
Movement remains active, body fat continues accumulating and the fetus gradually develops a fuller and less wrinkled appearance.
Understanding Pregnancy Week 31
Pregnancy Week 31 is part of the third trimester.
Mayo Clinic identifies this week as the stage when rapid weight gain becomes increasingly important after most major fetal development has taken place.
ACOG similarly states that at Week 31 major development is largely finished and the fetus begins gaining weight very quickly.
This does not mean development is complete.
The lungs, brain, nervous system and other organs continue important maturation throughout the remaining pregnancy.
How Big Is the Fetus at Pregnancy Week 31?
The NHS describes the fetus at Week 31 as approximately 41.1 centimeters from head to heel.
This is roughly comparable to the size of a coconut.
Week-by-week fetal measurements are population-based approximations. Individual fetuses can be somewhat smaller or larger.
A single online length estimate cannot determine whether an individual fetus is growing normally.
Rapid Fetal Weight Gain at Week 31
One of the clearest Week 31 developmental themes is rapid weight gain.
Mayo Clinic states that most major fetal development has taken place by this week and that it is now time for the fetus to gain weight quickly.
ACOG also specifically identifies rapid weight gain as a Week 31 feature.
A large proportion of the remaining pregnancy will involve adding body mass while organs continue to mature.
Body Fat and a Plumper Appearance
The NHS describes the Week 31 fetus as getting plumper day by day and looking progressively less wrinkled.
The change occurs partly because increasing amounts of fat are developing beneath the skin.
Fat stores will contribute to the fuller newborn appearance seen closer to term.
They are also important for helping with temperature regulation after birth.
Fetal Movement During Pregnancy Week 31
The NHS describes the fetus as very active during Week 31.
Movements can include kicking, stretching, rolling, turning, finger sucking and occasional larger position changes.
ACOG also describes stretching, kicking and grasping movements during Weeks 29 through 32.
Leg movements can feel increasingly powerful.
You may feel longer pushing or stretching sensations.
Larger changes in fetal position can noticeably alter the shape of the abdomen.
Hand movements continue becoming increasingly coordinated.
Does Movement Decrease Because the Uterus Is More Crowded?
Movements may feel different as the fetus becomes larger, but they should not simply stop because there is less space.
It is important to become familiar with your baby's usual movement pattern.
ACOG notes that decreased fetal movement deserves clinical attention because maternal perception of movement is an important indicator of fetal wellbeing.
Baby Position at Pregnancy Week 31
Some fetuses are already in a head-down position by Week 31.
Others may still be head up, sideways or moving between positions.
The NHS emphasizes that there is still time for a fetus that is head up to turn before birth.
Some babies do not descend into the pelvis until labor begins.
What If the Baby Is Breech at Week 31?
Breech means that the baby's bottom or feet are positioned toward the birth canal rather than the head.
A breech position at Week 31 does not automatically mean the fetus will remain breech at birth.
There is still time for spontaneous turning.
If breech presentation continues later in pregnancy, your maternity team can discuss assessment and birth-planning options.
Finger Sucking and Feeding Practice
The NHS describes the Week 31 fetus as actively sucking the fingers.
Sucking movements are part of the continuing development of skills that will eventually be important for feeding.
These movements occur together with swallowing and other developing oral reflexes.
A fetus does not need to be seen sucking a finger on ultrasound for normal development.
Recognizing Voices Outside the Womb
The fetal auditory system has been developing for many weeks.
The NHS Week 31 guide notes that the fetus can begin recognizing voices outside the uterus.
Sounds reaching the fetus are filtered through maternal tissue and amniotic fluid, so hearing inside the uterus is different from hearing after birth.
Talking naturally around the pregnancy is enough; there is no need to play excessively loud sounds against the abdomen.
Eye and Light Development at Pregnancy Week 31
Week 31 falls within the ACOG Weeks 29 through 32 developmental period in which the eyes can open and close and sense changes in light.
The visual system continues maturing.
Being able to detect changes in light does not mean the fetus has mature newborn or adult vision.
There is no need to use bright lights against the abdomen to test fetal eyesight.
Bone Marrow Continues Forming Red Blood Cells
ACOG identifies red-blood-cell formation in the bone marrow as an important feature of Weeks 29 through 32.
This process was already well established by Week 30 and continues during Week 31.
Red blood cells transport oxygen through the developing fetal circulation.
Blood-cell production continues maturing as pregnancy progresses.
Scalp Hair and Lanugo at Week 31
The fetal head may now have noticeable hair.
Hair amount varies widely between fetuses and does not indicate whether the pregnancy is healthier or more advanced.
Meanwhile, the soft body hair called lanugo is entering the period when it gradually begins to disappear.
Lanugo loss is gradual, and some may remain later in pregnancy or even be visible at birth.
Amniotic Fluid and Fetal Urination
The fetal kidneys have been producing urine for many weeks.
The NHS notes at Week 31 that the amount of amniotic fluid surrounding the fetus is increasing because the fetus can urinate.
Amniotic fluid cushions the fetus and supports normal movement and development.
Its volume is regulated by several fetal and maternal processes and can be assessed clinically when necessary.
Brain and Nervous System Development
Although most major fetal structures have developed by Week 31, the brain remains in an important period of maturation.
Neural connections continue developing, and the nervous system coordinates increasingly complex movement and sensory responses.
Brain development will continue rapidly throughout the remaining pregnancy and long after birth.
Lung Development at Pregnancy Week 31
The lungs continue maturing during the third trimester.
Surfactant production, which began earlier, continues as pregnancy advances.
Surfactant helps prevent collapse of the tiny air sacs after air breathing begins following birth.
The fetus does not breathe air inside the uterus and continues receiving oxygen through the placenta.
Additional gestational time allows important respiratory maturation to continue.
Pregnancy Week 31 Development Timeline
Weight accumulation becomes one of the major developmental priorities.
Increasing fat gradually smooths the fetal skin.
The fetus remains active with kicks, stretches, turns and grasping motions.
Some fetuses are head down while others still have time to turn.
The fetus responds to sound and the eyes can sense changes in light.
The brain, lungs and nervous system continue important development.
Maternal Changes During Pregnancy Week 31
Your uterus and abdomen continue growing as the third trimester progresses.
Symptoms that appeared in earlier weeks can continue or become more noticeable.
The NHS lists possible Week 31 symptoms including sleeping problems, backache, heartburn, constipation, leg cramps, dizziness, swelling, hemorrhoids and round ligament discomfort.
Braxton Hicks contractions may also become noticeable.
Braxton Hicks Contractions at Pregnancy Week 31
Braxton Hicks contractions are temporary uterine tightenings that are often described as practice contractions.
The NHS notes that at Week 31 the bump may tighten for around 20 to 30 seconds and then relax.
Typical Braxton Hicks contractions are generally irregular and should not progressively become stronger and closer together.
They typically do not develop into a consistent labor pattern.
The abdomen can briefly feel hard or tight before relaxing.
Changing position, resting or hydration may sometimes reduce ordinary practice tightenings.
Regular or painful contractions at Week 31 require prompt professional assessment.
Signs of Preterm Labor at Week 31
Pregnancy Week 31 is still preterm.
ACOG defines preterm labor as labor that begins before 37 weeks.
Possible symptoms include:
Regular or frequent contractions or uterine tightening can be a warning sign even when not very painful.
New pressure in the pelvis or lower abdomen can occur with preterm labor.
A constant, low, dull backache can be a warning symptom.
Watery, bloody or mucus-like discharge, increased discharge or a gush or trickle of fluid needs assessment.
Fundal Height and Uterine Growth at Week 31
Fundal height measures the distance between the pubic bone and the top of the uterus.
It is commonly used during prenatal visits to help follow uterine and fetal growth.
A measurement that differs from expected patterns does not automatically mean there is a problem.
Maternal body characteristics, fibroids, fetal position, multiple pregnancy and other factors can influence fundal height.
What May Happen at a 31-Week Prenatal Appointment?
Prenatal schedules vary by country and individual pregnancy.
In NHS maternity care, a specific Week 31 appointment is generally offered if this is the first baby.
That appointment can include:
Blood pressure may be checked for pregnancy-related hypertension.
A urine sample may be checked as part of routine prenatal assessment.
Fundal height may be measured to follow uterine growth.
Your baby's usual movement pattern may be discussed.
Birth preparation, mental wellbeing and previous screening results may also be discussed.
Sleeping Problems at Pregnancy Week 31
Sleeping difficulties can continue or become more noticeable as your abdomen grows.
Common interruptions can include fetal movement, frequent urination, heartburn, backache, leg cramps and difficulty finding a comfortable position.
Side sleeping can be more comfortable in later pregnancy.
ACOG notes that side sleeping may help avoid pressure from the uterus on a major blood vessel when compared with lying flat on the back.
Heartburn and Indigestion at Week 31
Heartburn can remain troublesome during the third trimester.
Pregnancy hormones can relax the muscle between the stomach and esophagus, while the growing uterus increases pressure within the abdomen.
Smaller meals, avoiding meals close to bedtime and remaining upright after eating may help some people.
Ask a healthcare professional or pharmacist about pregnancy-safe treatment if symptoms remain difficult to control.
Pelvic Floor Exercises at Pregnancy Week 31
The pelvic floor muscles help support the bladder, bowel and uterus.
Pregnancy places increasing pressure on these muscles.
The NHS recommends pelvic floor exercises during pregnancy and notes that they may help reduce urine leakage when laughing, coughing or sneezing.
If you are unsure how to perform pelvic floor exercises correctly, ask your midwife, physiotherapist or other healthcare professional.
Possible Pregnancy Week 31 Symptoms
Physical discomfort and frequent waking can interfere with sleep.
Indigestion and reflux may remain noticeable.
Posture and the growing abdomen can increase strain on the back.
Calf and foot cramps can occur, particularly at night.
Mild swelling of the feet or ankles can occur during pregnancy.
Temporary irregular uterine tightening may become more noticeable.
Preeclampsia Awareness at Week 31
Blood-pressure monitoring remains important during the third trimester.
Preeclampsia can develop after 20 weeks and sometimes occurs without obvious symptoms.
Vaccination Considerations Around Week 31
Vaccination recommendations depend on country, season and individual medical circumstances.
Current 2026 ACOG guidance recommends Tdap during every pregnancy between 27 and 36 weeks, preferably early in that window.
Week 31 therefore remains within the recommended U.S. Tdap period.
Other maternal vaccines, including RSV vaccination, have different gestational and seasonal timing requirements.
Healthy Choices During Pregnancy Week 31
Eat a Balanced Diet
Continue eating a variety of vegetables, fruits, protein foods, whole grains and other nutrient-rich foods.
Stay Hydrated
Drink regularly according to your activity, climate and individual medical needs.
Keep Moving When Appropriate
The NHS recommends around 150 minutes of pregnancy-appropriate physical activity each week for people able to exercise safely.
Individual recommendations should be adjusted when pregnancy complications or other medical issues are present.
Rest When Needed
Third-trimester fatigue and sleep disruption can make additional rest helpful.
Do Not “Eat for Two”
The NHS emphasizes that pregnancy does not require doubling food intake.
Nutritional needs should focus on a balanced diet and individualized professional guidance.
Pregnancy Week 31 and Your Estimated Due Date
Pregnancy is conventionally dated 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.
At Week 31, a pregnancy dated to 40 weeks has roughly nine weeks remaining.
This does not mean birth will occur exactly nine weeks later. An estimated due date is a planning estimate rather than a guaranteed delivery date.
What Happens After Pregnancy Week 31?
Pregnancy Week 32 brings continued rapid growth.
Mayo Clinic specifically highlights visible toenails at Week 32.
The soft body hair called lanugo also starts disappearing more noticeably around this stage.
The fetus continues gaining weight while the lungs, brain, nervous system and other organs mature.
Pregnancy Tools You May Find Useful
Estimate your expected delivery date using relevant pregnancy dating information.
Estimate the current gestational week from an appropriate pregnancy starting date.
Estimate a possible conception date or range while recognizing natural biological variation.
See approximately how much estimated time remains until your expected due date.
When Professional Healthcare Guidance Is Important
Week-by-week pregnancy information is general education and cannot determine whether an individual fetus or pregnancy is developing normally.
Seek prompt professional assessment for heavy vaginal bleeding, suspected fluid leakage, regular or frequent contractions, severe abdominal pain, fever, fainting or other worrying symptoms.
Changes in fetal movement, severe headache, vision changes, sudden face or hand swelling, significant one-sided leg pain or swelling, chest pain or severe breathing difficulty also need professional attention.
Pregnancy Week 31 FAQs
What happens during Pregnancy Week 31?
During Pregnancy Week 31, most major fetal development has taken place and rapid weight gain becomes increasingly important while the brain, lungs, nervous system and other organs continue maturing.
How big is the fetus at 31 weeks?
The NHS describes the fetus as around 41.1 centimeters from head to heel at Pregnancy Week 31, approximately the size of a coconut.
Is fetal development finished at Week 31?
Most major structural development has taken place by Week 31, but development is not finished. The brain, lungs, nervous system and other organs continue maturing while the fetus gains weight rapidly.
How active is the fetus at Pregnancy Week 31?
The fetus remains very active at Week 31 and may kick, stretch, turn, suck the fingers and make grasping movements. Become familiar with your baby's usual movement pattern.
Should the baby be head down at 31 weeks?
Some babies are already head down at Week 31, but it is not necessary for every fetus to be in the final birth position yet. There is still time for position to change.
Are Braxton Hicks contractions normal at Week 31?
Braxton Hicks contractions can occur at Week 31 and usually feel like temporary irregular tightening. Painful, regular or increasingly frequent contractions need prompt assessment because Week 31 is still preterm.
Why is sleep difficult at Pregnancy Week 31?
Sleep may be disturbed by the growing abdomen, fetal movement, frequent urination, heartburn, leg cramps, backache and difficulty finding a comfortable position.
What symptoms are common at Pregnancy Week 31?
Possible Week 31 symptoms include sleeping problems, backache, heartburn, constipation, leg cramps, dizziness, swelling, hemorrhoids, round ligament discomfort and Braxton Hicks contractions.
When should I call about contractions at Week 31?
Contact your maternity team promptly for regular or frequent contractions or tightening, pelvic pressure, a constant low backache, watery or bloody discharge, increased discharge or suspected fluid leakage.
What happens during Pregnancy Week 32?
During Pregnancy Week 32, fetal growth continues, toenails are visible, lanugo begins disappearing and the brain, lungs and other organs continue maturing while body weight increases.
Medical References and Further Reading
This Pregnancy Week 31 guide uses current medical and public-health information for general educational context.
NHS:
Antenatal Care and Appointments
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:
Special Tests for Monitoring Fetal Well-Being
Next: Pregnancy Week 32
During Pregnancy Week 32, fetal growth continues, toenails become visible, lanugo begins disappearing more noticeably and the brain, lungs and other organs continue maturing.
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