Results of case–control studies
| Studies finding significant association | Studies not finding significant association | ||||
| Studies, n | Participants in studies, n | Studies, n | Participants in studies, n | ||
| Birth outcomes | Caesarean delivery | 12 | 651 224 | 16 | 9751 |
| Premature delivery (<37 weeks) | 10 | 648 804 | 16 | 9807 | |
| Small for gestational age | 1 | 219 | 10 | 648 318 | |
| Low birth weight | 1 | 2130 | 1 | 110 | |
| Neonatal outcomes | Admission to neonatal care | 8 | 432 512 | 11 | 306 407 |
| Need for non-invasive respiratory support | 2 | 88 238 | 0 | 0 | |
| Need for mechanical ventilation | 2 | 88 238 | 0 | 0 | |
| Neurological disease | 1 | 79 | 1 | 88 159 | |
| Necrotising enterocolitis | 0 | 0 | 0 | 0 | |
| Other gastrointestinal disease | 0 | 0 | 0 | 0 | |
| Sepsis | 0 | 0 | 2 | 88 214 | |
| Infant outcomes | Hearing impairment | 2 | 191 | 0 | 0 |
| Developmental outcomes | 0 | 0 | 0 | 0 | |
| Any breast feeding (exclusive or mixed feeding) | 2 | 145 | 2 | 88 422 | |
| Infant or neonatal death | 0 | 0 | 10 | 96 688 | |