. 2022 Jul 19;6:80. [Version 1] doi: 10.12688/gatesopenres.13666.1

Table 1. Potential sources of bias in low birthweight data.

Potential sources of bias in birthweight data	Likely effect * on LBW prevalence estimates
1. Coverage of weighing: bias in newborns weighed at birth
1.1 Many newborns in LMIC countries are not weighed at birth, especially if born at home. These are more likely to be socio-economically disadvantaged and at higher risk of LBW.	Decreased
1.2 Extremely preterm or sick babies, those stillborn or dying soon after birth and those born around threshold of viability are the most likely to not be weighed. These babies are at high risk of being LBW.	Decreased
2. Coverage of data system: bias in newborns included in data source
2.1 Low coverage of administrative data systems in many low- and middle-income countries (e.g., lower coverage of birth registration for those who die shortly after birth, missing home births, and births in private facilities even if weighed). Births in private facilities are more likely to be socioeconomically advantaged and at lower biological risk of LBW; however, high prevalence of medical interventions (e.g., caesarean sections both indicated and elective before 37 weeks) may increase risk of LBW.	Increased or decreased
3. Loss of birthweight data: biases in missing birthweight data for newborns included in the data source and weighed at birth
3.1 In surveys, biases in card retention (e.g., birthweight not available for babies who died and who are more likely to have been LBW) or inability to recall birthweight accurately at the time of the survey.	Decreased
3.2 Missing administrative birthweight data on the sickest babies (frequently LBW) who are transferred immediately to (and weighed in) a newborn ward.	Decreased
4. Measurement errors: individual measurement or recording error
4.1 Heaping of recording of birthweight on 2500g. As definition excludes babies with birthweight exactly 2500g, those LBW newborns with birthweight near the threshold frequently heaped at 2500g.	Decreased
4.2 Errors in birthweight measurement (e.g., poorly calibrated scales, inappropriate devices), suboptimal weighing practices (e.g., clothed, or delayed weighing until >1 day after birth).	Increased or decreased
4.3 Extremely preterm or sick babies and those born around threshold of viability who die soon after birth are more likely to be misclassified as stillbirth. These babies are at high risk of being LBW.	Decreased
5. Measurement unit error
5.1 Confusion in surveys where birthweights may be provided in both pounds and grams (e.g., LBW baby weighing 4.0 lbs. recorded as 4.0 kg).	Decreased
6. Denominator calculation errors in LBW prevalence calculation
6.1 LBW prevalence calculated as: number with birthweight <2500 per all livebirths (whether weighed or not).	Decreased

* Decreased - the potential bias is likely to lead to a decreased LBW prevalence; Increased - the potential bias is likely to lead to an increased LBW prevalence.