Inclusion criteria
Studies were initially identified based on their title and abstract and later included after a full-text evaluation. Observational studies were included if they met all of the following criteria: used a cohort study design, explored whether maternal neuraminidase inhibitor use during pregnancy increased the risk of adverse maternal or neonatal outcomes, and had sufficient available data to allow the calculation of risk estimates if adjusted data were not provided. Reviews, letters to the editor, or conference abstracts; basic studies or those using animal experiments; case reports or series; studies without a control group; and studies that included other congenital malformations where it was not possible to separate the data regarding oral clefts were excluded.
Data extraction and quality assessment Data were independently extracted by two investigators, and any discrepancies were resolved by the third author. The extracted information included author names, publication date, study design, study location, study period, drug exposure assessment results, outcome measures, statistical analyses used, and study quality. The most-adjusted effect size estimate was used when more than one estimate was provided. The risk of bias was estimated using the Newcastle Ottawa Scale to assess the nonrandomized study quality[14], as recommended by the Cochrane Collaboration. The risk of bias concerning selection, comparability, and assessment of the exposure/outcome was estimated according to nine items using a star allocation scheme. The scale features eight criteria and yields scores ranging from 0 (high risk of bias) to 9 (low risk of bias). Studies with scores > 7 were considered high quality. Summary bias risk assessments were derived for each study.