| References | Outcomes | Risk of bias domains a | Tier b | |||||
|---|---|---|---|---|---|---|---|---|
| KEY – detection bias ‐ exposure | KEY – detection bias ‐ outcome | KEY – confounding bias | Selection bias | Attrition/exclusion bias | Other sources of bias | |||
| Case–control studies | ||||||||
| Johansen et al. ( 2008 ) | Cleft lip with or without cleft palate or cleft palate only | + | ++ | + | ++ | ++ | + | 1 |
| Botto et al. ( 2001 ) | Transposition of the great arteries, double‐outlet right ventricle, tetralogy of Fallot, truncus arteriosus, and supracristal ventricular septal defect | + | ++ | + | ++ | ++ | + | 1 |
| Shaw et al. ( 1997 ) | Neural tube defects | + | + | –– | + | + | + | 2 |
| Mills et al. ( 1997 ) | Neural tube defects | – | ++ | –– | – | ++ | + | 2 |
| Martínez‐Frías and Salvador ( 1990 ) | Any birth defect | – | + | –– | + | + | + | 2 |
| Prospective studies | ||||||||
| Michikawa et al. ( 2019 ) | Congenital diaphragmatic hernia | – | ++ | + | ++ | + | + | 2 |
| Mastroiacovo et al. ( 1999 ) | Major malformations | NR | – | –– | – | – | – | 3 |
| Rothman et al. ( 1995 ) | Any birth defect, cranial neural‐crest defects, neural tube defects, musculoskeletal or urogenital defects or other defects | ++ | + | ++ | + | ++ | + | 1 |
| Bille et al. ( 2007 ) | Cleft lip with or without cleft palate or cleft palate only | – | + | + | + | + | + | 2 |
a
Expert judgement was translated into a rating scale for each question to be answered as follows: (++): definitely low RoB; (+): probably low RoB; (NR): not reported; (−): probably high RoB; (− −): definitively high RoB.
b
The individual rating for each question was combined by an algorithm and translated to an overall tier of reliability for each individual study (RoB tier 1: low RoB; RoB tier 2: moderate RoB; RoB tier 3: high RoB).