Results
Figure 1 presents the flow of studies through the present review
selection process. After screening 15,281 records, 59 records
representing 44 studies were assessed for eligibility based on the full
text. Finally, 18 studies including 827,382 participants were included
in the qualitative synthesis; 15 studies including 825,622 participants
were included in quantitative synthesis. Supplementary Table S3 lists
all excluded studies with reasons for exclusion. We did not find any
ongoing or unpublished studies by searching study registries. By
contacting authors, we obtained unpublished data from two studies23, 25.
Table 1 shows the characteristics of the included studies. Nine studies
(810,197 participants) used population-based samples, 2 (6,915
participants) were multicentre studies, 6 (9,439 participants) were
single-centre studies, and 1 (831 participants) did not specify the
study setting. Supplementary Table S4 shows the details of the inclusion
and exclusion criteria of the included studies. All studies were
conducted in high-income countries, mostly between the late 1990s and
early 2010s. The studies included participants of non-Hispanic White,
Hispanic, African, Asian, or Indian descent. Two studies (28,722
participants) only included women about to deliver their first child.
Two studies (140,714 participants) compared pregnant women born preterm
and at full term, 9 (216,439 participants) compared women born with and
without LBW, and 4 (468,469 participants) compared women born with and
without SGA status. The remaining 3 studies (1,760 participants) only
compared the mean birth weight of women with or without GDM. Figure S1
presents a summary of study quality assessment using the QUIPS tool37. The overall quality of the included
studies was moderate to low, mainly due to uncontrolled confounders.