Pregnancy week 23 is an important stage of the second trimester. The fetus is becoming stronger, more active and more proportionate, while the lungs, bone marrow, nervous system and fat stores continue developing.

One of the most interesting milestones this week is rapid eye movement, or REM sleep. ACOG notes that at week 23, most of the fetus’s sleep time is spent in REM sleep. At the same time, the bone marrow begins producing blood cells, lower airways in the lungs are developing, and fat storage is increasing.

For the pregnant person, the expanding uterus and rib cage can make breathing feel slightly different. Rib discomfort, backache, heartburn, leg cramps and breast leakage may also become more noticeable.

Quick answer: At 23 weeks pregnant, the fetus is around 28.9 cm from head to heel, approximately the size of a large mango according to NHS guidance. The limbs are now proportionate, kicks are getting stronger, breathing practice continues, sleep–wake patterns are developing, and fetal REM sleep is becoming a major part of sleep.

What Does 23 Weeks Pregnant Mean?

Pregnancy is usually dated from the first day of the last menstrual period (LMP).

At 23 weeks pregnant, conception typically occurred around 21 weeks earlier in a conventional menstrual cycle.

You remain in the second trimester.

This stage of fetal development increasingly focuses on:

• stronger movement;
• sleep and nervous-system development;
• lung growth;
• blood-cell production;
• fat accumulation;
• increasing body proportion.

The fetus has moved far beyond the early organ-formation phase, but many systems remain immature and continue developing rapidly.

How Big Is the Baby at 23 Weeks?

The NHS estimates the fetus at around 28.9 cm from head to heel at week 23.

That is approximately the size of a large mango.

The NHS also notes that the fetal limbs are now in proportion.

This means the arms and legs are looking more balanced relative to the rest of the body than they did earlier in pregnancy.

Exact measurements vary according to:

• genetics;
• the exact day within week 23;
• fetal position;
• normal biological variation;
• ultrasound technique.

What Is Developing at 23 Weeks?

MedlinePlus describes weeks 23–25 as a distinct developmental phase when:

• bone marrow begins making blood cells;
• the lower airways of the lungs develop;
• the fetus begins storing fat.

ACOG adds that week 23 is particularly notable because most fetal sleep time is spent in REM sleep.

These changes make week 23 different from the earlier weeks focused mainly on lanugo, fingerprints and stronger movement.

What Is REM Sleep?

REM stands for rapid eye movement.

In older children and adults, REM sleep is associated with:

• active brain patterns;
• rapid eye movements;
• dreaming.

At week 23, ACOG notes that most fetal sleep time is spent in this REM phase.

This is an important sign of developing neurological organization.

It should not be interpreted to mean that fetal sleep is identical to adult sleep.

Does the Baby Dream at 23 Weeks?

We cannot reliably say that a fetus “dreams” in the same way an older child or adult does.

Although REM sleep is strongly associated with dreaming after birth, fetal brain development is still incomplete.

It is more accurate to say that the fetus is developing REM sleep patterns, not to assume a specific mental experience.

Does the Baby Have a Sleep Schedule?

The NHS notes that the fetus is practicing breathing and getting into patterns of sleeping and waking around week 23.

These patterns may not match the pregnant person’s routine.

You may sometimes notice more movement when:

• sitting quietly;
• lying down;
• trying to sleep.

That may partly reflect your ability to notice movement more easily when you are less active.

Is the Baby Moving More at 23 Weeks?

Yes.

Fetal muscles and nervous-system coordination are improving.

The NHS notes that over the coming weeks you may be kicked around more strongly and may eventually see the abdomen move.

Movements can include:

• kicks;
• turns;
• rolls;
• stretches;
• arm movements;
• whole-body shifts.

Should You Feel Movement at 23 Weeks?

Many pregnant people can feel fetal movement clearly by this stage.

However, intensity varies.

Movement may feel like:

• kicks;
• taps;
• rolls;
• fluttering;
• pushing;
• shifting.

Placental position and fetal position can still influence how strongly movements are felt.

Can You See the Belly Move at 23 Weeks?

Possibly, though it becomes more common over the next several weeks.

The NHS notes that stronger kicks may eventually become visible from outside the abdomen.

At week 23, some people may notice small visible movements while others will not.

Both can occur.

Should You Count Kicks at 23 Weeks?

Formal kick counting is not usually required this early.

However, the NHS advises getting to know the baby’s usual rhythms and speaking with a midwife if movement slows down.

At this stage, the goal is not to reach a fixed number.

It is to gradually become familiar with what movement feels like for your pregnancy.

What If the Baby Seems Quieter?

Fetal activity can vary because of:

• sleep;
• fetal position;
• placental location;
• how busy you are;
• whether the fetus is facing inward or outward.

But if movement becomes noticeably slower than what you have come to expect, contact your maternity healthcare provider.

Do not rely on a home Doppler to reassure yourself.

Is Bone Marrow Making Blood Cells at 23 Weeks?

Yes.

MedlinePlus states that during weeks 23–25, bone marrow begins making blood cells.

Earlier in fetal life, organs such as the liver played a major role in blood-cell production.

As development progresses, bone marrow increasingly takes over this function.

Why Is Bone Marrow Important?

Bone marrow is the tissue inside bones that eventually produces important blood components, including:

• red blood cells;
• many white blood cells;
• platelets.

At week 23, this system is beginning to take on more of its long-term role.

Are the Lungs Developing at 23 Weeks?

Yes.

MedlinePlus notes that the lower airways of the lungs develop during weeks 23–25.

The NHS also notes that the fetus is practicing breathing movements.

However, the lungs remain immature.

The fetus does not breathe air.

What Are the Lower Airways?

The lower respiratory tract includes branching structures that eventually carry air deeper into the lungs.

These developing structures help form the framework for later gas exchange.

Substantial lung maturation is still required before breathing outside the uterus becomes possible.

Does the Baby Breathe Amniotic Fluid?

The fetus makes breathing-like movements involving fluid rather than air.

These movements help develop:

• respiratory muscles;
• chest-wall movement;
• lung structures.

Oxygen continues to come through the placenta and umbilical cord.

Are the Lungs Ready to Work Outside the Womb?

No.

At 23 weeks, lung development is still very immature.

Important structures and substances needed for independent breathing develop further later in pregnancy.

Avoid interpreting “practice breathing” as meaning the lungs are ready for ordinary breathing.

Is the Baby Starting to Store More Fat?

Yes.

MedlinePlus notes that fat storage begins increasing during weeks 23–25.

Fat will become increasingly important for:

• energy storage;
• skin appearance;
• temperature regulation after birth;
• overall fetal growth.

The fetus still looks much leaner than a full-term newborn.

Why Does Fetal Fat Matter?

Fat has several important roles.

Later in pregnancy, it helps:

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

Fat accumulation becomes especially rapid in later pregnancy.

What Is Happening to the Skin?

The skin remains relatively thin and wrinkled.

Blood vessels may still be visible through it.

As fat increases beneath the skin, the body gradually begins looking fuller.

Lanugo remains present and helps interact with the protective coating over fetal skin.

Are Eyebrows and Hair Still Developing?

Yes.

Features that appeared earlier continue becoming more defined.

These include:

• eyebrows;
• eyelashes;
• scalp hair;
• lanugo.

Hair thickness and color at this stage do not reliably predict what the newborn’s hair will eventually look like.

Are Fingerprints Still Developing?

Yes.

The ridges forming fingerprints and footprints continue becoming more established.

These patterns are unique to each individual.

Even identical twins have different fingerprints.

Can the Baby Hear at 23 Weeks?

Yes.

Hearing became functional earlier in the second trimester and continues maturing.

The fetus is exposed to:

• heartbeat;
• blood-flow sounds;
• digestive sounds;
• the pregnant person’s voice;
• outside sounds.

Sounds are filtered by maternal tissues and amniotic fluid.

Can the Baby React to Sound?

Movement may sometimes occur after a sound.

However, not every movement following a noise represents a deliberate reaction.

The auditory system and brain are still developing.

Is Talking to the Baby Useful?

You can talk or sing if you enjoy it.

The fetus is increasingly exposed to your voice.

There is no need for loud sound or special “brain development” audio programs.

Normal everyday sound exposure is sufficient.

What Is Happening to the Placenta?

The placenta continues functioning as the fetal support organ.

It helps:

• supply oxygen;
• deliver nutrients;
• remove carbon dioxide;
• remove metabolic waste;
• produce pregnancy hormones.

The placenta continues adapting as fetal growth accelerates.

What Is Happening in Your Body at 23 Weeks?

The uterus is becoming substantially larger.

This can place more pressure on:

• ribs;
• diaphragm;
• back;
• digestive organs.

The NHS specifically notes two changes around week 23:

• rib pain;
• feeling more breathless than usual.

Why Can Your Ribs Hurt at 23 Weeks?

The NHS explains that rib discomfort may occur as the rib cage expands to accommodate the growing pregnancy.

Pain may be related to:

• expanding rib cage;
• changing posture;
• growing uterus;
• muscle strain.

Mild discomfort can occur, but severe chest or upper abdominal pain deserves medical assessment.

Why Can You Feel Short of Breath?

As the uterus grows, it can alter how the diaphragm and lungs move.

The NHS notes that you may feel somewhat more breathless as the growing fetus places increasing pressure upward.

Mild breathlessness can occur during pregnancy.

However, sudden or severe breathing difficulty is not something to dismiss.

When Is Breathlessness Concerning?

Seek urgent medical assessment if breathlessness:

• starts suddenly;
• is severe;
• occurs at rest;
• is associated with chest pain;
• is accompanied by fainting;
• occurs with a racing heart or other alarming symptoms.

Online pregnancy information cannot diagnose the cause.

Can Your Breasts Leak at 23 Weeks?

Yes.

The NHS notes that breasts may begin leaking colostrum, the early form of breast milk.

Colostrum may appear:

• yellowish;
• creamy;
• clear.

Some people leak during pregnancy and others do not.

Neither pattern predicts future milk supply.

What Is Colostrum?

Colostrum is the first milk produced by the breasts.

It is rich in:

• antibodies;
• proteins;
• nutrients.

After birth, it helps support the newborn’s immune system and early feeding needs.

Should You Express Colostrum at 23 Weeks?

Do not routinely start expressing colostrum this early unless your healthcare professional specifically advises it.

Antenatal colostrum expression, when recommended, is generally discussed much later and depends on individual circumstances.

What Symptoms Are Common at 23 Weeks?

The NHS lists possible symptoms including:

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

Is Back Pain Normal?

Mild backache is common as the pregnancy grows.

Possible contributors include:

• changing posture;
• increasing abdominal weight;
• ligament relaxation;
• shifting center of gravity.

Useful measures may include:

• supportive footwear;
• gentle movement;
• appropriate lifting technique;
• posture awareness.

Is Rib Pain the Same as Round Ligament Pain?

No.

Round-ligament pain usually affects the:

• lower abdomen;
• side of the uterus;
• groin.

Rib discomfort is higher in the torso and may relate to expansion and posture.

Significant pain should always be assessed according to its location and severity.

Is Heartburn Common?

Yes.

Pregnancy hormones relax digestive muscles while the growing uterus changes abdominal pressure.

Helpful measures can include:

• smaller meals;
• eating slowly;
• avoiding personal trigger foods;
• remaining upright after eating.

Ask a healthcare professional about pregnancy-safe treatment if needed.

Is Constipation Normal?

Yes.

Hormonal changes and some iron supplements can slow bowel movement.

Helpful measures include:

• water;
• fruit;
• vegetables;
• whole grains;
• legumes;
• appropriate physical activity.

Are Hemorrhoids Still Common?

Yes.

Constipation and increasing pelvic pressure can contribute to hemorrhoids.

Avoiding excessive straining and keeping stools soft can help.

Seek medical advice for significant bleeding or severe pain.

Are Leg Cramps Normal?

Yes.

Leg cramps often occur during pregnancy.

Gentle stretching and hydration may help.

Seek urgent medical advice for one leg that becomes persistently:

• swollen;
• red;
• hot;
• painful.

Is Swelling Normal at 23 Weeks?

Mild swelling can occur.

Sudden or pronounced swelling—particularly with severe headache, vision changes or feeling unwell—should be medically assessed.

Is Vaginal Discharge Normal?

White or milky vaginal discharge can be normal.

Seek medical advice if discharge becomes:

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

Persistent watery leakage should also be assessed.

What About Bleeding?

Any pregnancy bleeding deserves medical attention.

The NHS specifically advises seeking medical advice for bleeding.

Seek urgent evaluation for:

• heavy bleeding;
• severe pain;
• fainting;
• severe dizziness.

Are Braxton Hicks Contractions Possible at 23 Weeks?

Some people may begin noticing occasional uterine tightening during the second trimester.

These are often called Braxton Hicks contractions.

They are usually:

• irregular;
• brief;
• not progressively stronger.

However, regular painful contractions, pressure, bleeding or fluid leakage at 23 weeks require medical assessment because they can have other causes.

What Does Braxton Hicks Feel Like?

It may feel like the abdomen briefly becomes:

• firm;
• tight;
• hard.

The sensation then relaxes.

Do not diagnose repeated painful tightening on your own.

At this gestation, concerning contractions deserve professional advice.

Is the Anatomy Scan Already Finished by 23 Weeks?

Many people will have completed the routine anatomy scan by now because ACOG generally recommends the structural ultrasound at 18–22 weeks.

If your scan was incomplete or showed something that requires follow-up, additional imaging may be scheduled.

A follow-up scan does not automatically mean something serious is wrong.

Why Might You Need Another Ultrasound?

Reasons can include:

• fetal position blocked some views;
• a structure could not be seen clearly;
• growth requires follow-up;
• placenta location needs reassessment;
• a finding needs specialist review.

The reason should be explained by your maternity team.

What If My Anatomy Scan Was Normal?

A normal anatomy scan is reassuring.

However, it cannot detect every possible:

• genetic condition;
• congenital condition;
• developmental problem.

Continue routine prenatal care even after a normal result.

What If an Abnormality Was Found?

Depending on the finding, care may involve:

• specialist ultrasound;
• maternal-fetal medicine consultation;
• genetic counseling;
• diagnostic testing;
• later monitoring.

Avoid trying to interpret isolated ultrasound terminology using search results alone.

What Prenatal Tests Are Coming Next?

One important test window is approaching: gestational diabetes screening.

ACOG states that glucose screening is usually performed between 24 and 28 weeks of pregnancy.

Week 23 is therefore a useful time to know what is coming next.

What Is Gestational Diabetes?

Gestational diabetes is diabetes first diagnosed during pregnancy.

It occurs when blood glucose becomes higher than recommended during pregnancy.

It may occur even in someone who did not have diabetes before pregnancy.

Why Is Gestational Diabetes Screening Done?

High blood glucose can affect both maternal and fetal health.

ACOG recommends glucose screening because gestational diabetes can often be managed effectively once identified.

When Is the Glucose Test Done?

ACOG states that routine glucose screening is generally performed between 24 and 28 weeks if earlier testing was not indicated.

People with certain diabetes risk factors may be tested earlier.

What Happens During Glucose Screening?

ACOG describes the common screening approach as:

1. drinking a glucose-containing drink;
2. waiting about one hour;
3. having blood drawn.

If the result is elevated, a longer diagnostic glucose test may be recommended.

An abnormal screening result does not automatically mean you have gestational diabetes.

Should You Change Your Diet Before the Glucose Test?

Do not try to “beat” the test by dramatically altering your food intake unless your healthcare service specifically gives preparation instructions.

The test is intended to assess how your body handles glucose under standard conditions.

Follow the instructions provided by your clinic.

Is Anemia Still Important in the Second Trimester?

Yes.

Iron requirements rise during pregnancy.

ACOG identifies iron deficiency as one of the most common causes of anemia during pregnancy.

Your prenatal team may monitor blood counts according to your healthcare system and individual risk.

What Are Possible Symptoms of Anemia?

Possible symptoms can include:

• fatigue;
• weakness;
• dizziness;
• shortness of breath.

However, these symptoms also overlap with ordinary pregnancy changes.

A blood test—not symptoms alone—is needed to diagnose anemia.

Should You Automatically Take Extra Iron?

No.

Some prenatal vitamins already contain iron.

Additional iron may be recommended based on:

• blood tests;
• diet;
• medical history;
• individual clinical needs.

High-dose iron can also worsen constipation, so supplementation should be appropriate to your situation.

Is Healthy Eating Important at Week 23?

Yes.

The NHS emphasizes that there is still no need to eat for two, and no additional calories are generally required until the third trimester under UK guidance.

Focus on:

• fruit;
• vegetables;
• whole grains;
• protein;
• iron-rich foods;
• calcium-rich foods;
• healthy fats;
• adequate hydration.

Is Caffeine Safe?

Caffeine should remain within your country’s pregnancy recommendations.

The NHS specifically encourages reducing excessive tea and coffee intake around this stage.

Remember caffeine can also be present in:

• energy drinks;
• cola;
• chocolate;
• some medicines.

Is Vitamin D Important?

Yes.

Vitamin D contributes to healthy bones and muscles.

NHS guidance recommends 10 micrograms daily for certain pregnant people depending on season and individual circumstances in the UK.

Recommendations vary by country.

Follow your own healthcare provider’s guidance.

Can You Exercise at 23 Weeks?

For many uncomplicated pregnancies, yes.

The NHS recommends around 150 minutes of activity per week during pregnancy.

Appropriate activity may include:

• walking;
• swimming;
• pregnancy-adapted strength training;
• prenatal exercise.

Adjust as your balance changes.

Can Exercise Help Back Pain?

Appropriate activity can help maintain:

• strength;
• mobility;
• posture.

But exercise should not be used to push through significant pain.

Persistent back or pelvic pain may benefit from medical or physiotherapy assessment.

Are Pelvic Floor Exercises Still Important?

Yes.

Pregnancy places increasing pressure on pelvic-floor muscles.

Regular exercises can support:

• bladder control;
• pelvic support;
• postpartum recovery.

If you are unsure how to perform them correctly, ask a pelvic-health physiotherapist.

Is Sun Sensitivity Higher During Pregnancy?

The NHS notes that pregnancy can make skin more sensitive to sunlight and recommends sensible sun protection.

Helpful measures include:

• shade;
• protective clothing;
• suitable sunscreen.

This is especially useful if pregnancy pigmentation such as melasma has developed.

Is Whooping Cough Vaccination Still Relevant?

Vaccination timing depends on your country.

In the NHS program, whooping cough vaccination is offered during pregnancy and can be given from 16 to 32 weeks.

Follow the vaccination schedule recommended by your own healthcare system.

Should You Think About Work and Maternity Leave?

This may be a useful time.

The NHS notes that, under UK rules, pregnancy should generally be disclosed to an employer by around week 25 to meet certain maternity-notification requirements.

Employment rules differ by country, so check your local laws.

Can You Travel at 23 Weeks?

For many uncomplicated pregnancies, travel remains possible.

Consider:

• access to maternity care;
• travel insurance;
• infection risks;
• food and water safety;
• prolonged sitting;
• your pregnancy history.

Long journeys may require movement breaks and hydration.

Is Sex Safe at 23 Weeks?

For many uncomplicated pregnancies, sexual activity remains safe.

Seek personalized medical advice if you have:

• bleeding;
• leaking fluid;
• placenta-related problems;
• cervical concerns;
• painful contractions;
• instructions to avoid intercourse.

When Should You Seek Medical Help at 23 Weeks?

Seek professional advice whenever symptoms concern you.

Urgent medical assessment may be needed for:

• heavy vaginal bleeding;
• severe abdominal or pelvic pain;
• regular painful contractions;
• continuing fluid leakage;
• fainting;
• severe or sudden shortness of breath;
• chest pain;
• high fever;
• severe one-sided leg swelling or pain;
• severe headache with vision changes;
• a meaningful decrease in fetal movement once you have established a usual pattern.

Online information cannot safely diagnose these symptoms.

Pregnancy Week 23 FAQs

How big is the baby at 23 weeks?

The NHS estimates the fetus at around 28.9 cm from head to heel, approximately the size of a large mango.

What is developing at 23 weeks?

Bone marrow begins producing blood cells, lower lung airways develop, fetal fat storage increases, and sleep organization continues developing.

Does the baby have REM sleep at 23 weeks?

Yes. ACOG states that at week 23, most fetal sleep time is spent in REM sleep.

Can you feel the baby move at 23 weeks?

Many people can feel clear kicks, rolls and turns. Movement is becoming stronger.

Should you count kicks at 23 weeks?

Formal kick counting is not usually necessary yet, but you should gradually become familiar with your baby’s usual movement rhythms.

Are the baby’s limbs in proportion?

Yes. The NHS notes that the limbs are now proportionate to the rest of the fetal body.

Are the lungs developing?

Yes. The lower airways are developing during weeks 23–25, though the lungs remain immature.

Is bone marrow making blood cells?

Yes. MedlinePlus identifies the beginning of bone-marrow blood-cell production during weeks 23–25.

Is the baby gaining fat?

Yes. Fetal fat storage begins increasing during this stage.

Can colostrum leak at 23 weeks?

Yes. The NHS notes that some pregnant people may notice colostrum leaking from the breasts.

Is rib pain normal?

Mild rib discomfort can occur as the rib cage expands and the uterus grows. Severe pain should be medically assessed.

Is breathlessness normal?

Mild breathlessness can occur as pregnancy progresses, but sudden or severe breathlessness, chest pain or fainting requires urgent assessment.

When is gestational diabetes screening done?

ACOG states that glucose screening is usually performed between 24 and 28 weeks.

Is week 23 part of the second trimester?

Yes. Week 23 remains within the second trimester.

What Comes Next?

During Pregnancy Week 24, you reach another important developmental stage. Fetal movements continue strengthening, lung development progresses, fat storage increases, and the body continues preparing for more rapid growth.

By the end of week 24, ACOG notes that the fetus is around 12 inches long and weighs about 1½ pounds.

Week 24 also marks the beginning of the usual 24–28 week gestational-diabetes screening window.

Previous: Pregnancy Week 22
Next: Pregnancy Week 24
Tool: Pregnancy Due Date Calculator

Medical References

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

• NHS — 23 Weeks Pregnant
• MedlinePlus — Fetal Development
• American College of Obstetricians and Gynecologists (ACOG) — Changes During Pregnancy
• ACOG — How Your Fetus Grows During Pregnancy
• ACOG — Routine Tests During Pregnancy
• ACOG — Gestational Diabetes
• ACOG — Anemia in Pregnancy

Editorial & Medical Information

Last content review: October 2026

This article provides general educational pregnancy information only. It does not diagnose pregnancy complications, assess fetal wellbeing, interpret fetal movement, prescribe supplements or medication, or replace individualized prenatal care.

Pregnancy symptoms, fetal movement and medical needs vary between individuals. Contact a qualified healthcare professional for personal concerns about movement, bleeding, severe pain, fluid leakage, contractions, breathing difficulty or other symptoms.

Conclusion

Pregnancy week 23 is a distinctive stage of neurological, respiratory and blood-system development. ACOG notes that most fetal sleep at this stage occurs in REM sleep, while MedlinePlus describes the beginning of bone-marrow blood-cell production, lower-airway lung development and increasing fetal fat storage during weeks 23–25.

The NHS estimates the fetus at around 28.9 cm from head to heel and notes that the limbs are now proportionate. Breathing practice and increasingly organized sleeping and waking patterns are also developing, while fetal kicks become stronger.

For the pregnant person, week 23 may introduce rib discomfort, increased breathlessness and leaking colostrum as the uterus, rib cage and breasts continue adapting to pregnancy.

This is also a useful time to prepare for the next major prenatal testing window. ACOG recommends routine gestational-diabetes screening at 24–28 weeks for people who have not already required earlier diabetes testing.

Continue evidence-based prenatal care, balanced nutrition and appropriate physical activity. Heavy bleeding, severe pain, regular painful contractions, continuing fluid leakage, sudden severe breathlessness or a concerning reduction in established fetal movement should be assessed medically rather than self-diagnosed online.