Study selection
Studies were eligible for inclusion if they were observational cohort or
case-control studies. Case reports or series were excluded from the
present review. We included studies that involved pregnant women
regardless of study setting. The exposures of interest were the infancy
parameters of presently pregnant women and were defined as follows: LBW,
birth weight <2500 g 13; small for
gestational age (SGA), birth weight <10th percentile for the
given gestational age, stratified by sex, using the average weight of
gestational age 30; and preterm birth,
gestational age of <37 weeks 31.
When data on both birth weight and gestational age were reported, we
extracted data on birth weight in preference. The comparator group
comprised women who were not born small or born at full term.
The outcome of interest was GDM, as defined by the International
Association of Diabetes Pregnancy Study Groups (IADPSG), World Health
Organization (WHO), American Diabetes Association or Endocrine Society,
or International Classification of Diseases 11th revision (ICD-11) or
earlier 32-36. If studies used other
definitions, they were included in the present review; however, we
removed them to assess the robustness of the pooled estimates. For
studies that reported LBW, preterm birth, or SGA as a risk factor in
pregnant women without reporting the association with GDM, we contacted
study authors to acquire estimates of such associations, where
available. These additional estimates were included in the present
analysis, provided they were measures of an association between at least
one of the exposure factors and the outcome of interest.
Two investigators independently screened article titles and abstracts to
shortlist relevant studies; subsequently, the same sets of authors
assessed the full text for study eligibility. In cases where data were
incomplete and precluded study eligibility assessment, we contacted
study authors with requests for clarification. Multiple publications
were assessed together; the record with the most complete data was
included in the present review.
Data extraction and
quality assessment
Two investigators independently extracted data from all included
studies, using a pilot-tested, uniform data extraction sheet.
Any discrepancies between
reviewers were resolved through consensus between two reviewers or
arbitration by a third reviewer, as required. For studies that compared
three or more exposure groups, we contacted study authors to obtain data
comparing two groups of interest. In cases where this approach was
unsuitable, we extracted the relevant data, as reported, and performed
subgroup comparisons between the two groups subdivided by specific
thresholds (i.e., birth weight 2500 g, <10th percentile, and
gestational age 37 weeks for LBW, SGA, and preterm birth, respectively),
as this approach may have resulted in conservative effect estimates. The
same authors who performed data extraction also independently assessed
the risk of bias in each study, using the Quality In Prognosis Studies
(QUIPS) tool 37. We prospectively identified
the following candidate confounders: age, obesity, smoking status,
socioeconomic status, diabetes mellitus before the index gestation, and
family history of diabetes 38, 39.