Low birthweight
A good start in life begins in the womb
In 2020, 19.8 million newborns, an estimated 14.7 per cent of all babies born globally that year, suffered from low birthweight. These babies were more likely to die during their first month of life and those who survived face lifelong consequences including a higher risk of stunted growth,[1], lower IQ [2] ,and adult-onset chronic conditions such as obesity and diabetes [3]. To grow a healthy baby, mothers need good nutrition and rest, adequate antenatal care, and a clean environment. Together, these ingredients for a healthy pregnancy can help to prevent, identify and treat the conditions that cause low birthweight and thus foster achievement of the World Health Assembly (WHA) nutrition target to reduce low birthweight by 30 per cent between 2012 and 2030.
Progress on reducing low birthweight prevalence has been slow or lacking in all regions. The largest decrease occurred in South Asia, where prevalence dropped 4.5 percentage points over 20 years (from 29.4% [credible interval (CrI): 25.9-33.4] in 2000 to 24.9% [CrI: 21.1-29.8] in 2020). There were small decreases in prevalence from 2000-2020 in West and Central Africa, Eastern and Southern Africa, and Europe and Central Asia. Several regions saw either no change or a slight increase in prevalence from 2000-2020, including Latin America and the Caribbean, North America, the Middle East and North Africa, and East Asia and the Pacific.
At the global level, the annual average rate of reduction (AARR) in low birthweight prevalence was only 0.30 per cent per year between 2012 and 2020, yet an AARR of 1.96 per cent per year is required between 2012 and 2030 to meet the WHA low birthweight target by 2030. Even the region with the largest decrease in prevalence, South Asia, was well below the required AARR, at 0.85 per cent from 2012 to 2020.
From 2000-2020 the annual number of babies born with low birthweight dropped by 2.3 million globally (from 22.1m [CrI: 20.7-23.9] in 2000 to 19.8m [CrI: 18.4-21.7] in 2020).
In most regions progress on reducing the number of low birthweight babies was either stagnant or non-existent over the same time period, including in West and Central Africa, East and Southern Africa, the Middle East and North Africa, and North America. In Sub-Saharan Africa the small decrease in low birthweight prevalence from 2000-2020 was more than offset by an increase in births, resulting in a small increase in the number of babies born with low birthweight.
Three regions saw a slight decrease in the number of low birthweight babies: East Asia and the Pacific, Latin America and the Caribbean, and Europe and Central Asia. The only region that achieved a substantial reduction in the number of babies born with low birthweight from 2000-2020 was South Asia, where the number decreased by 3.1 million (from 11.7m [CrI:10.4-13.4] in 2000 to 8.7m [7.4-10.4] in 2020).
While South Asia saw the most progress in reduction of low birthweight for both prevalence and absolute numbers, more than 40 per cent of babies born with low birthweight in 2020 were born in South Asia. In 2020, more than 70 per cent of all low birthweight newborns in the world were born in just 3 regions: South Asia (44 per cent of all low birthweight births worldwide), Eastern and Southern Africa (14 per cent of all low birthweight births worldwide) and West and Central Africa (14 per cent of all low birthweight births worldwide).
Only 14 countries are on track to achieve the World Health Assembly global target on low birthweight with 10 of them being in Northern America, Europe, and Australia and New Zealand. Across all regions, the majority of countries are showing no progress. Asia and Latin America and Caribbean have the largest proportion of countries with a reversal in progress and make up nearly three quarters of all countries showing a reversal in progress globally.
Low birthweight babies who are not weighed at birth may not receive the specialized care they need to survive and thrive; and it is not possible to effectively monitor newborn health in countries with a very high percentage of newborns without a birthweight in national data sources.
Globally, birthweight data were not available for 28.7 per cent of newborns in 2023 (using data from 2012-2021). These estimates reflect newborns who were not weighed and those who were weighed but whose birthweights were not captured by key data sources.
More than half of newborns born in West and Central Africa (54.8 per cent) and East and Southern Africa (50.7 per cent) did not have a birthweight in their most recent national data source; and close to one out of three newborns born in South Asia (30.8 per cent) and the Middle East and North Africa (34.3 per cent) lacked a recorded birthweight.
References
- Christian P, et al. Black RE. Risk of childhood undernutrition related to small-for-gestational age and preterm birth in low- and middle-income countries. International Journal of Epidemiology 2013;42:1340–55
- Gu H, Wang L, Liu L, et al. A gradient relationship between low birth weight and IQ: A meta-analysis. Sci Rep. 2017;7(1):18035. Published 2017 Dec 21. doi:10.1038/s41598-017-18234-9
- Jornayvaz FR, Vollenweider P, Bochud M, Mooser V, Waeber G, Marques-Vidal P. Low birth weight leads to obesity, diabetes and increased leptin levels in adults: the CoLaus study. Cardiovasc Diabetol. 2016; 15: 73.
- Jornayvaz FR, Vollenweider P, Bochud M, Mooser V, Waeber G, Marques-Vidal P. Low birth weight leads to obesity, diabetes and increased leptin levels in adults: the CoLaus study. Cardiovasc Diabetol. 2016; 15: 73.
Low birthweight
Low birthweight data
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Notes on the data
- Definitions
Two key indicators about birthweight are described in this section, (i) low birthweight (LBW) prevalence and (ii) prevalence of newborns without birthweight data in national data sources.
Birthweight is the first weight of the newborn obtained after birth. For live births, birthweight should preferably be measured within the first hour of life, before significant post-natal weight loss has occurred. Low birthweight is defined as less than 2,500 grams (up to and including 2,499 grams).
The prevalence of newborns without birthweight data reflects newborns who were not weighed and those who were weighed but whose birthweights were not captured by key data sources. Estimates of newborns without birthweight data from administrative systems (e.g., Health Management Information Systems) include unweighed births and weighed births not recorded in the system. Estimates from household surveys include births where weight was not available from an official document (e.g., health card) or could not be recalled by the respondent at the time of interview.
| Indicator | Numerator | Denominator |
| Prevalence of low birthweight | The number of live births that weigh less than 2,500 grams in a given time-period [1] | Total number of live births with a birthweight in the same time-period |
| Prevalence of newborns without birthweight data
(from household surveys)
|
Total number of live births for which a valid [2] birthweight was not available from an official document (e.g., health card) or could not be recalled by the respondent at the time of interview. | Total number of live births in the survey sample. |
| Prevalence of newborns without birthweight data
(from administrative sources)
|
Total number of live births which were not weighed and weighed births not recorded in the administrative system in a calendar year. | Total number of live births captured in the administrative data source in a calendar year.
|
[1] Typically a calendar year for administrative sources and two to five years for household surveys.
[2] A valid birthweight is biologically plausible, defined as ≥250g and ≤5500g.
- Low birthweight data sources and methods
Nationally representative estimates of LBW prevalence can be derived from a range of sources, broadly defined as administrative data or nationally representative household surveys. National administrative data come from national systems, including civil registration and vital statistics (CRVS) systems, national health management information systems (HMIS), and birth registries. Nationally representative household surveys include Demographic and Health Surveys (DHS), Multiple Indicator Cluster Surveys (MICS), and other national surveys for which microdata are available for re-analysis.
The 2023 development of the country, regional and global database with annual LBW estimates from 2000 to 2020 built on previous rounds of LBW estimation (2004 and 2019) and comprised the following steps:
a) Collect birthweight data from administrative sources and surveys, and screen those data with inclusion criteria to ensure quality of input data.
b) Adjust survey input data to account for LBW underestimation due to missing values and heaping.
c) Produce annual LBW estimates using statistical modelling
d) Convene country consultations to validate input data and modelled LBW estimates, and refine data/estimates when necessary to finalize estimates.
The LBW database was developed through a collaborative effort between UNICEF, WHO, and London School of Hygiene and Tropical Medicine (LSHTM). The three partner organizations formed a steering group and working groups for estimation, and were guided by the Expert Consultative Group (ECG) and the Guidelines for Accurate and Transparent Health Estimates Reporting (GATHER) throughout the estimation process. The Expert Consultative Group is an advisory group comprised of global experts in preterm birth and LBW measurement, including obstetricians, neonatologists, statisticians, preterm birth researchers and programme staff. LBW estimation, which was carried out alongside preterm birth estimation for the first time in 2023, received ethical approval from LSHTM. A basic description of the 2023 LBW estimation steps are available in Annex 2 of the forthcoming UNICEF-WHO Low Birthweight Estimates Report; and the full, detailed methods are available in publications on the LBW estimation protocol and findings (1,2).
- Newborns without a birthweight in national data sources
3.1 Country data sources
Data for newborns without birthweight came from the same sources used to estimate low birthweight, with some important caveats.
Low birthweight estimation used all collected data, which included multiple sources and multiple years of data for many countries. Given issues with the comparability of estimates for the percentage of newborns without a birthweight in the data source for the differing levels of quality for administrative data, only administrative data sources in the highest quality category as described in Annex 2 of the forthcoming UNICEF-WHO Low Birthweight Estimates Report and surveys were used for this database. As the global and regional estimates were to cover one recent time-period, only the most recent source for each country, which was more recent than 2011, were used. Globally, there were 12 countries with no recent data (i.e., latest data was from 2011 or earlier) and 43 countries with no administrative data source in the highest quality category or survey.
3.2 Estimation of country-level prevalence of newborns without a birthweight in the data source
For countries with recent administrative data in the highest quality category as described in Annex 2 of the forthcoming UNICEF-WHO Low Birthweight Estimates Report, the prevalence of newborns without a birthweight in the data source was calculated by summing the number of live births reported to weigh <2500g and ≥2500 g in one calendar year in the source and then dividing the sum by the number of annual live births in the United Nations Population Division World Population Prospects (UNPD-WPP) 2022 Revision for the same year.
Estimates from household surveys represent the percentage of live births occurring in the survey reference period (e.g., in the last 2 years, in the last 5 years, etc.,) among women of reproductive age as defined by the survey (generally women aged 15–49 years), without a birthweight in the dataset. Of note is that for some surveys, all births for each sampled woman are included in the data collection on birthweights and for other surveys only the last live birth is included in the data collection. For household surveys, the prevalence of newborns without a birthweight in the data source was calculated by dividing the number of live births with a valid birthweight (defined as ≥250g and ≤5500g) in the survey reference period by the total number of live births in the survey reference period. The prevalence estimates from surveys were weighted using woman’s sample weight and calculation of confidence intervals took into account complex sample design (i.e., clusters and strata).
3.3 Regional and global estimates
The regional and global population-weighted estimates were weighted using the annual number of live births in 2021 from the UNPD-WPP 2022 Revision. Population-weighted averages for any given region were generated by (a) multiplying the prevalence estimate for each country with available data in the required time period by the number of births in 2021 in that country; (b) summing all of the country specific products; and (c) dividing the sum of the products by the total number of births in all countries with data in 2021. Population coverage, or the share of the population for which an estimate is available, was calculated by dividing the number of births in 2021 in countries with data by the total number of births in each respective region in 2021. The standard used for minimum population coverage (i.e., minimum population coverage required to display the population-weighted regional estimate) is 50 per cent.
References for notes on the data
- Krasevec J, Blencowe H, Coffey C et al.Study protocol for UNICEF and WHO estimates of global, regional, and national low birthweight prevalence for 2000 to 2020. Gates Open Res 2022, 6:80 (https://doi.org/10.12688/gatesopenres.13666.1)
- UNICEF and WHO (2022). Technical note for country consultation on low birthweight and preterm birth estimates.