| Database | Date of search | Results | Results after deduplication |
| MEDLINE (Ovid) | 1 October 2018 | 2537 | 2480 |
| Embase (Ovid) | 1 October 2018 | 2947 | 1471 |
| Maternity and Infant Care (Ovid) | 1 October 2018 | 2336 | 1068 |
| CINAHL Plus (Ebsco) | 21 September 2018 | 2770 | 1505 |
| CENTRAL (Wiley) | 1 October 2018 | 1875 | 449 |
| total | 12465 | 6973 | |
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