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Low birth weight, prematurity and growth retardation: small vulnerable newborns

  • Page updated onApril 22, 2026
Small vulnerable newborns
Text and photo: Bruno Abarca

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.

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.
  • Being born with both conditions simultaneously: premature and also small for gestational age (around 1.1%) (Lawn et al., 2023)Lawn, J. E., Ohuma, E. O., Bradley, E., et al. (2023). Small babies, big risks: Global estimates of prevalence and mortality for vulnerable newborns to accelerate change and improve counting. The Lancet, 401(10389), 1707–1719. https://doi.org/10.1016/S0140-6736(23)00522-6.

These three categories make it possible to identify a much larger group of at-risk children than was traditionally grouped under the term low birthweight newborn. The new terminology, introduced in 2023, moves beyond categorisation based on a relatively arbitrary threshold of 2,500g birth weight (UNICEF & WHO, 2019)UNICEF & WHO. (2019). UNICEF-WHO low birthweight estimates: Levels and trends 2000–2015. World Health Organization. https://www.unicef.org/reports/UNICEF-WHO-low-birthweight-estimates-2019, introduced around 1918 and formalised by WHO in 1950 (Hughes et al., 2017)Hughes, M. M., Black, R. E., & Katz, J. (2017). 2500-g low birth weight cutoff: History and implications for future research and policy. Maternal and Child Health Journal, 21(2), 283–289. https://doi.org/10.1007/s10995-016-2131-9. The new category of vulnerable newborns now also includes premature or small-for-age babies who, despite being born above that weight threshold, face similar risks to their lives. The focus is now also placed on the different underlying biological causes of the problem and on how to address each of them through prevention and clinical management.

It is estimated (based on 2020 data) that 14.7% of all live births are low birthweight (<2,500g), equivalent to 1 in every 7 (Okwaraji et al., 2024)Okwaraji, Y. B., Krasevec, J., Bradley, E., et al. (2024). National, regional, and global estimates of low birthweight in 2020, with trends from 2000: A systematic analysis. The Lancet, 403(10431), 1071–1080. https://doi.org/10.1016/S0140-6736(23)01198-4. This percentage exceeds 15% in places such as Southern and Western Africa, and is even above 20% in India and the Philippines (UNICEF, 2023)UNICEF. (2023). Low birthweight. UNICEF Data. https://data.unicef.org/topic/nutrition/low-birthweight/.

Low birth weight newborns
UNICEF, 2023

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 attributable to preterm birth, 14.7% to being small for gestational age, and 7.7% to the combination of both conditions, totalling 55.3% of all neonatal deaths (Lawn et al., 2023)Lawn, J. E., Ohuma, E. O., Bradley, E., et al. (2023). Small babies, big risks: Global estimates of prevalence and mortality for vulnerable newborns to accelerate change and improve counting. The Lancet, 401(10389), 1707–1719. https://doi.org/10.1016/S0140-6736(23)00522-6.

In addition to neonatal deaths from this cause, foetal deaths must also be considered, as many small vulnerable babies do not survive to be born alive. The problems that can lead to preterm or low birthweight births are the same ones that increase the risk of foetal death. Despite this, foetal mortality, which is largely preventable, has received very little attention or recognition as a public health priority. It is often overlooked, and excluded from global indicators and targets that are calculated solely on the basis of live births (Lawn et al., 2023)Lawn, J. E., Ohuma, E. O., Bradley, E., et al. (2023). Small babies, big risks: Global estimates of prevalence and mortality for vulnerable newborns to accelerate change and improve counting. The Lancet, 401(10389), 1707–1719. https://doi.org/10.1016/S0140-6736(23)00522-6.

Small and vulnerable newborns who survive the neonatal period also carry a lifelong risk of health and developmental problems. Among the consequences are growth problems and increased risk of malnutrition, delayed cognitive development and learning difficulties, a higher risk of childhood illnesses (such as asthma, epilepsy, behavioural problems, and vision and hearing impairments), and chronic diseases in adult life such as hypertension, cardiovascular problems, type 2 diabetes, and metabolic syndrome. All of this, of course, ultimately impacts their education, employment opportunities, social outcomes, and income (Ashorn et al., 2023)Ashorn, P., Ashorn, U., Muthiani, Y., et al. (2023). Small vulnerable newborns — big potential for impact. The Lancet, 401(10389), 1692–1706. https://doi.org/10.1016/S0140-6736(23)00354-9.

Small vulnerable newborns
Ashorn, 2023

Known causes of prematurity and low birth weight: malnutrition, infections and environmental factors

Why do cases of small vulnerable newborns occur?

Although the mechanisms leading to a small vulnerable newborn differ, their causes overlap. These include contextual factors such as poverty, conflict, and low maternal education (Mahumud et al., 2017)Mahumud, R. A., Sultana, M., & Sarker, A. R. (2017). Distribution and determinants of low birth weight in developing countries. Journal of Preventive Medicine and Public Health, 50(1), 18–28. https://doi.org/10.3961/jpmph.16.087, health system weaknesses, environmental pollution, and gender inequality. These factors increase exposure to the immediate causes of preterm birth and intrauterine growth restriction. Three of them account for nearly half of all cases: maternal malnutrition, infections during pregnancy, and environmental factors (Hunter et al., 2023)Hunter, P. J., Awoyemi, T., Ayede, A. I., et al. (2023). Biological and pathological mechanisms leading to the birth of a small vulnerable newborn. The Lancet, 401(10389), 1720–1732. https://doi.org/10.1016/S0140-6736(23)00573-1.

Maternal malnutrition can be related to insufficient nutrient and energy reserves for proper foetal development and growth, and can be diagnosed through low weight and height, low BMI, or reduced mid-upper arm circumference (Kapil & Ververs, 2023)Kapil, S., & Ververs, M. (2023). Maternal mid-upper arm circumference: Still relevant to identify adverse birth outcomes in humanitarian contexts? Field Exchange, 70. https://www.ennonline.net/fex/70/en/maternal-mid-upper-arm-circumference-still-relevant-identify-adverse-birth-outcomes. However, it can also manifest as micronutrient deficiencies such as iron, zinc, and calcium. These influence the functioning of enzymes and hormones involved in foetal growth, placental function, the balance of hormones related to the onset of labour, maternal immunity, blood pressure (and the risk of pre-eclampsia), foetal 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 leading to the birth of small and vulnerable newborns become better understood, so too does their prevention.

Eight interventions are recommended that can be offered throughout antenatal care. These are multiple micronutrient supplements, protein-energy supplements, aspirin administration, treatment of syphilis cases, smoking cessation education, malaria prevention, treatment of asymptomatic bacteriuria, and vaginal progesterone administration.

Alongside these, there are three further interventions that appear to have great potential, although they are still being researched. These are the administration of omega-3 fatty acid supplements, calcium, and zinc (Hofmeyr et al., 2023)Hofmeyr, G. J., Black, R. E., Rogozinska, E., et al. (2023). Evidence-based antenatal interventions to reduce the incidence of small vulnerable newborns and their associated poor outcomes. The Lancet, 401(10389), 1733–1744. https://doi.org/10.1016/S0140-6736(23)00355-0.

Impact of 11 interventions on SVN
Hofmeyr, 2023

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-constrained settings, many women attend their first antenatal visit very late, receive none at all, or receive antenatal care of very poor quality, in which these proven-effective interventions are not available (Le & Nguyen, 2019)Le, K., & Nguyen, M. (2019). Armed conflict and birth weight (MPRA Paper No. 102162). University Library of Munich. https://mpra.ub.uni-muenchen.de/102162/.

🧠 Let's pause and reflect

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 body of evidence-based recommendations for the clinical management of small and vulnerable newborns (McGrath, 2023)replace. These include kangaroo mother care (WHO, 2025)(WHO, 2025) and skin-to-skin contact with the mother (or another caregiver), exclusive breastfeeding whenever possible, and iron supplementation, among other measures (WHO, 2022)World Health Organization. (2022). WHO recommendations for care of the preterm or low-birth-weight infant. World Health Organization. https://www.who.int/publications/i/item/9789240058262.

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 children with acute and chronic malnutrition (Kerac et al., 2025)Kerac, M., James, P. T., McGrath, M., Brennan, E., Cole, T., Opondo, C., & Frison, S. (2025). Malnutrition in infants aged under 6 months: Prevalence and anthropometric assessment — analysis of 56 low- and middle-income country DHS datasets. BMJ Global Health, 10(5), e016121. https://doi.org/10.1136/bmjgh-2024-016121. It therefore makes less and less sense to address their needs through separate and fragmented theoretical frameworks, medical and nutritional approaches, and protocols (Kerac et al., 2025)Kerac, M., Ashorn, P., Berkley, J. A., et al. (2025). Infants less than 6 months of age at risk of poor growth and development: Evidence gaps identified during WHO guideline development. BMJ Global Health, 10(Suppl. 5), e017227. https://doi.org/10.1136/bmjgh-2024-017227.

In this regard, the approach to managing nutritionally at-risk infants under six months and their mothers (known as the MAMI Care Pathway) can serve as a bridge between the management of small and vulnerable newborns and acute malnutrition management in children under five (MAMI Global Network et al., 2021)MAMI Global Network, Emergency Nutrition Network, & London School of Hygiene and Tropical Medicine. (2021). MAMI Care Pathway Package (Version 3). https://www.ennonline.net/mami/resources/en/mami-care-pathway-package-version-3-2021.

The community-based MAMI Care Pathway approach is adapted to humanitarian contexts and resource-constrained settings. Focused on the needs of the mother-infant pair -- the mother and her small, nutritionally at-risk baby (in the 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 comprehensive support for their survival and wellbeing (Desplats et al., 2026)Desplats, G., Dent, N., Ben Ameur, A., & Kitamura, T. (2026). MAMI en pratique: Learning from the field – Technical brief. Emergency Nutrition Network. https://doi.org/10.71744/z6j7-wa12. This support is linked to other available systems, facilitating referral to health services when there are serious problems, and interventions addressing the mother's needs, such as micronutrient supplementation and mental health and psychosocial support (Fuller et al., 2025)Fuller, S., Dent, N., Deconinck, H., & McGrath, M. (2025). Supporting mothers of vulnerable infants under six months: Inviting conversation and collaboration. Emergency Nutrition Network. https://www.ennonline.net/resource/mami/supporting-mothers-vulnerable-infants-under-six-months-inviting-conversation.

References

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How to cite this page

Abarca, B. (April 22, 2026). Low birth weight, prematurity and growth retardation: small vulnerable newborns. Salud Everywhere. https://saludeverywhere.com/en/health-in-humanitarian-crises/small-vulnerable-newborns/

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