Description of the Studies
Among the 1774 studies identified in the database research, 32 matched
the eligibility criteria (Figure 1). Of these studies, 27 had a cohort
design, 2 had a cross-sectional design, 2 case-controls, and 1 was a
randomized clinical trial.
18 studies had a full-term control group, 12 described the prevalence in
the extremely preterm group, 17 described the prevalence in the very
preterm group, and 8 described the prevalence in the moderate/late
preterm group. Only 6 studies described more than one prematurity group
according to gestational age, and 2 of them were classified by birth
weight instead of gestational age, thus were excluded from the
gestational age analysis.