Low birth weight, prematurity and growth retardation: small vulnerable newborns
- Page updated onApril 8, 2026
Approximately, for every four live births, one falls into the category of small and vulnerable newborns, which includes preterm, small for gestational age, and those who meet both conditions simultaneously. These three subcategories encompass, practically, the totality of what has traditionally been known as "low birth weight newborns", but with more clarity as to the causal pathways of their vulnerability.
The problem, of course, most affects newborns whose mothers experience pregnancy exposed to malnutrition, gender-based violence, disease, poverty and conflict. The consequences are experienced for years, when those who have not suffered premature death live at greater risk of wasting or stunting, illness, delayed development, and as a consequence have fewer opportunities for education, employment and to escape the cycle of intergenerational poverty.
Table of contents:
What are small vulnerable newborns?
The term includes babies who are too small and those who are born too early.
Often, adverse conditions experienced by some infants during the intrauterine period cause:
- Preterm births before 37 weeks of gestation (around 8.8% of all live newborns).
- At term but small below the 10th percentile for their gestational age (around 16.3%), as a consequence of intrauterine fetal growth retardation.
- Both problems at the same time: preterm and also small for their gestational age (around 1.1%).
These three categories make it possible to identify a much larger group of at-risk newborns than those traditionally grouped under the term low birth weight newborn. The new terminology, introduced in 2023, goes beyond categorization based on a relatively arbitrary threshold of 2500g, first introduced around 1918 and officialized by WHO in 1950. The new category of small vulnerable newborns now also includes preterm or small-for-gestational-age babies who, despite being born above that weight threshold, face similar risks to their survival. The focus has also shifted to the different underlying biological causes of the problem and how to address each of them through prevention and clinical management.
It is estimated (with 2020 data) that 14.7% of all live newborns have low birth weight (<2500g), which equals 1 in 7. This percentage exceeds 15% in regions such as Southern and Western Africa and is even higher than 20% in India and the Philippines.
What are the consequences of the vulnerability of small newborns?
Small and vulnerable newborns are at high risk of neonatal mortality. It is estimated that 32.8% of neonatal deaths are due to preterm birth, 14.7% to being small for gestational age, and 7.7% to a combination of both conditions, totaling 55.3% of neonatal deaths.
In addition to neonatal deaths from this cause, stillbirths must also be considered, as many vulnerable small babies are not born alive. The problems that can lead to preterm or low birth weight are the same as those that increase the risk of stillbirth. Despite this, stillbirth, much of it preventable, has received little attention or consideration as a public health priority. It is often ignored and left out of global indicators and targets that are only calculated on the basis of live births.
Small vulnerable newborns who survive the neonatal period also maintain a lifetime risk of health and developmental problems. Among the consequences are growth problems and increased risk of malnutrition, delayed cognitive development and learning difficulties, increased risk of diseases during childhood (such as asthma, epilepsy, behavioral problems, and vision and hearing problems), or chronic diseases in adulthood such as hypertension, cardiovascular problems, type 2 diabetes, or metabolic syndrome. All of this, of course, ends up impacting their education, job opportunities, social success and income.
Known causes of prematurity and low birth weight: malnutrition, infections and environmental factors
Why do cases of small vulnerable newborns occur?
Although the mechanisms that lead to a small vulnerable newborn differ, their causes overlap. These include contextual factors such as poverty, conflict, low maternal education, health system deficiencies, environmental pollution, and gender inequality. These factors increase exposure to the immediate causes of preterm birth and intrauterine growth retardation. Three of them explain almost half of the cases: maternal malnutrition, infections during pregnancy, and environmental factors.
Maternal malnutrition may be related to low nutrient and energy reserves for proper fetal growth and development, and can be diagnosed through low weight and height, low BMI, or reduced arm circumference. However, it can also manifest as deficiencies of micronutrients such as iron, zinc and calcium. These influence the functioning of enzymes and hormones involved in fetal growth, placental function, the balance of hormones related to the onset of labor, maternal immunity, blood pressure (and risk of preeclampsia), fetal oxygenation, and bone formation.
Among the main infections that result in small vulnerable newborns are malaria, HIV/AIDS and sexually transmitted infections. These can affect the placenta, cause anemia, produce hormonal imbalances, worsen the mother's nutritional status, cross the placental barrier and infect the fetus, and even trigger premature delivery.
Environmental factors include air pollution, intimate partner violence, physical overload, and alcohol and tobacco use. These affect the fetus and placenta through oxidative stress, physical and mental trauma, reduced uterine blood flow, premature uterine contractions, and placental toxicity.
Many cases of small vulnerable newborns can be prevented with prenatal care
As the mechanisms that lead to the birth of small vulnerable newborns become better understood, so does their prevention. There are eight recommended interventions that can be offered throughout antenatal care. These are multiple micronutrient supplementation, protein-energy supplementation, aspirin administration, syphilis case management, smoking cessation education, malaria prevention, treatment of asymptomatic bacteriuria, and vaginal progesterone administration. Along with these, there are three other interventions that appear to have great potential, although they are still under investigation. These are omega-3 fatty acid, calcium and zinc supplementation.
If implemented with the recommended coverage, the implementation of the first eight prenatal interventions could reduce total low birth weight newborns by 17.9%, stillbirths by 31.5%, and neonatal deaths by 20%. If the other three potential interventions were added to these eight, the reduction in low birth weight cases could reach 28.6%.
When considering these interventions from a public health and population impact perspective, we should highlight two of them: multiple micronutrient supplementation, and protein-energy supplementation. These two interventions are the only ones with proven effect in reducing the cases of small-for-gestational-age term newborns. Moreover, these two interventions alone, together, would account for 67.1% of the effect of the eleven recommended interventions in preventing cases of small and vulnerable newborns, and up to 32% of their effect in reducing neonatal mortality.
Unfortunately, in humanitarian crises and resource-poor settings, many women arrive at their first antenatal checkup very late, do not have any, or receive poor quality antenatal care, where these proven effective interventions are not available.
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How can a humanitarian organization already working on community-based management of acute malnutrition in under-fives expand that approach to include infants under six months of age and their mothers?
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Integrated management of small vulnerable newborns: from Kangaroo mother care to the MAMI Care Pathway
Beyond prevention, there is a series of recommendations based on scientific evidence for the clinical management of small and vulnerable newborns. These include the "kangaroo mother method" and skin-to-skin contact with the mother (or other caregiver), exclusive breastfeeding whenever possible, and iron supplementation, among other measures.
The MAMI Care Pathway approach responds to the needs of high-risk infants and their mothers.
Today's small and vulnerable newborns are tomorrow's acutely and chronically malnourished children. Therefore, it seems to make less and less sense to address their needs from different and fragmented theoretical frameworks, approaches and medical and nutritional protocols.
In this regard, the MAMI Care Pathway approach to the management of young, nutritionally at-risk children under six months of age and their mothers can serve as a bridge between the management of young, vulnerable newborns and the management of acute malnutrition in children under five years of age.
The community-based MAMI Care Pathway approach is adapted to humanitarian contexts and where resources are limited. Focused on the needs of the mother and young, nutritionally at-risk baby dyad (in their first six months of life), this approach provides technical guidance to identify them as early as possible, assess their psychosocial, nutritional and health problems and risks, and provide them with comprehensive support for their survival and well-being. This support is linked to the other available systems, thus facilitating referral to health services if there are serious problems, and interventions targeted to the mother's needs, such as micronutrient supplementation and mental health and psychosocial support actions.
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How to cite this page
Abarca, B. (April 8, 2026). Low birth weight, prematurity and growth retardation: small vulnerable newborns. Salud Everywhere. https://saludeverywhere.com/en/health-in-humanitarian-crises/small-vulnerable-newborns/
External links
- ENN, 2026. MAMI en pratique: Learning from the field.
- Kerac, 2025. Infants less than 6 months of age at risk of poor growth and development: evidence gaps identified during WHO guideline development.
- Kerac, 2025. Malnutrition in infants aged under 6 months: prevalence and anthropometric assessment.
- WHO, 2025. Kangaroo mother care: a clinical practice guide.
- Fuller, 2025. Supporting mothers of vulnerable infants under six months.
- Okwaraji, 2024. National, regional, and global estimates of low birthweight in 2020, with trends from 2000: a systematic analysis.
- UNICEF, 2023. Low birthweight.
- Ashorn, 2023. Small vulnerable newborns: big potential for impact.
- Lawn, 2023. Small babies, big risks: global estimates of prevalence and mortality for vulnerable newborns to accelerate change and improve counting.
- Hunter, 2023. Biological and pathological mechanisms leading to the birth of a small vulnerable newborn.
- Hofmeyr, 2023. Evidence-based antenatal interventions to reduce the incidence of small vulnerable newborns and their associated poor outcomes.
- McGrath, 2023. The Lancet «Small Vulnerable Newborns» series: Reflections from a «MAMI» perspective.
- Kapil, 2023. Maternal mid-upper arm circumference: Still relevant to identify adverse birth outcomes in humanitarian contexts?
- WHO, 2022. WHO recommendations for care of the preterm or low-birth-weight infant.
- MAMI Global Network, ENN, LSHTM, 2021. MAMI Care Pathway Package, Version 3.
- Le, 2019. Armed conflict and birth weight.
- UNICEF, WHO, 2019. Low birthweight estimates: levels and trends 2000-2015.
- Hughes, 2017. 2500-g Low Birth Weight Cutoff: History and Implications for Future Research and Policy.
- Mahumud, 2016. Distribution and Determinants of Low Birth Weight in Developing Countries.