WHO defines low birth weight as a birth weight below 2500 grams, regardless of gestational age.
How to read this guidance
Newborns have limited reserves and may show illness through feeding, temperature, colour, breathing or alertness rather than a specific complaint. The same observation can have several causes, so early professional assessment is safer than waiting for a textbook pattern.
The sections below retain the factual scope of the linked source. They add practical questions and safety-netting without claiming that a symptom, measurement or exposure proves a diagnosis in one child.
How does WHO define low birth weight?
WHO defines low birth weight as weight at birth below 2500 grams.
Is low birth weight the same as being born preterm?
No. WHO explains that low birth weight can result from prematurity, restricted growth before birth, or both. Birth weight and gestational age therefore describe different aspects of a newborn.
Why is low birth weight monitored?
WHO uses low birth weight as a population-level indicator of maternal, newborn and nutrition conditions. It is included in global nutrition monitoring because it is associated with important short- and long-term health outcomes.
What does WHO’s current global target brief say?
WHO’s 2025 policy brief describes low birth weight as a continuing global public-health problem and extends international attention to reducing its prevalence through 2030.
What to observe and record
- quality and frequency of feeds
- wet diapers, stool and weight trend
- temperature, colour and breathing pattern
- wakefulness, tone and the ease of settling
For a newborn topic, record feeding frequency and quality, wet diapers, stool, temperature, colour, breathing, wakefulness and any screening or discharge result. Note a clear change from the baby’s usual pattern and contact the newborn service promptly when the concern is worsening.
Practical next steps
- keep the birth, pregnancy, screening and discharge records together
- follow the feeding and follow-up plan given by the newborn team
- avoid unprescribed remedies, supplements or direct heat sources
- contact the maternity or newborn service promptly when feeding or behaviour changes
Follow the feeding, screening and follow-up plan provided by the maternity or newborn team. General online information cannot decide whether a newborn needs examination, testing or treatment, so seek early professional advice for a meaningful change in feeding, breathing, colour, temperature or alertness.
When urgent assessment is needed
- poor feeding with unusual sleepiness or weak cry
- grunting, chest indrawing, blue colour or breathing pauses
- fever, low temperature, seizure or difficulty waking
- very few wet diapers, repeated vomiting or rapidly increasing jaundice
Young infants and children with immune, heart, lung, blood, metabolic or neurologic conditions may need earlier assessment. Use local emergency services whenever delay could be dangerous.
Preparing for a healthcare visit
Bring pregnancy, birth, discharge, feeding and screening records. Ask what the finding means now, whether repeat testing or observation is needed, how feeding and hydration will be followed, and who should be contacted if the baby changes overnight.
If safe, a photograph of a changing rash or brief video of an unusual movement can help show what happened outside the clinic. Never delay emergency care to make a recording. For a possibly contagious illness, telephone ahead before entering a shared waiting area.
Following the plan at home
Make sure every caregiver understands the same plan. Record meaningful changes rather than checking constantly, protect rest and hydration, and keep follow-up appointments. Improvement in one symptom does not cancel a new red flag, while one mild symptom in an otherwise well child does not establish a serious condition.
Before leaving a visit, repeat the plan back in your own words: what to do today, when to follow up, whether school or childcare attendance should change, and where to go if the child worsens outside normal clinic hours.
Questions this page cannot answer for one child
This page cannot determine whether a newborn is feeding adequately, maintaining temperature, clearing jaundice or passing a screen. Those questions require the baby’s examination, measurements, history and follow-up plan.
Ask the healthcare professional how the child’s age and medical history change the interpretation, what alternative explanations remain possible, and whether observation, testing, referral or treatment is appropriate. When no test is needed, ask what expected improvement should look like and how long it is reasonable to wait.
Document who provided the advice, the planned review time and any agreed precautions so that another caregiver or service can understand what has already been assessed.
If the family faces language, transport, cost or access barriers, mention them directly. A safe plan must be practical enough to follow, and the service may be able to adjust timing, written instructions or referral arrangements.
Keep the original source link and review date with the notes so later readers can distinguish the published evidence from the individualized clinical plan.
Limits and source boundaries
Read the publication date and scope of the source. A global fact sheet may describe burden and prevention without providing a local treatment pathway; a surveillance or screening page may describe population practice without estimating one child’s risk.
Recommendations, schedules and available services differ by country and can change. Use the official source for its stated evidence and a qualified professional for decisions about the individual child.