Main characteristics of children included in the study
| Variable | Total (n=613) | Subcohort 1 (children born before 26 May 2020) (n=266) | Subcohort 2 (children born from 26 May 2020 on) (n=347) | P value |
| Gestational age at delivery | ||||
| <34 weeks | 6 (1.0) | 4 (1.5) | 2 (0.6) | 0.50 |
| 34–36 weeks | 21 (3.5) | 9 (3.5) | 12 (3.5) | |
| ≥37 weeks | 576 (95.5) | 247 (95.0) | 329 (95.9) | |
| Birth weight | ||||
| <2500 g | 35 (5.7) | 17 (6.4) | 18 (5.2) | 0.63 |
| 2500–4000 g | 552 (90.1) | 236 (88.7) | 316 (91.1) | |
| >4000 g | 26 (4.2) | 13 (4.9) | 13 (3.8) | |
| Birth size, mean±SD | 49.7±2.6 | 49.4±2.9 | 50.0±2.3 | 0.01 |
| Birth cephalic perimeter, mean±SD | 34.4±1.4 | 34.3±1.6 | 34.5±1.3 | 0.09 |
| Apgar 1′, mean±SD | 8.7±0.8 | 8.7±0.8 | 8.7±0.8 | 0.55 |
| Apgar 5′, mean±SD | 9.7±0.6 | 9.7±0.6 | 9.6±0.6 | 0.29 |
| pH, mean±SD | 7.24±0.31 | 7.23±0.47 | 7.26±0.08 | 0.31 |
| Gender | ||||
| Woman | 295 (48.4) | 119 (45.4) | 176 (50.7) | 0.20 |
| Man | 314 (51.6) | 143 (54.6) | 171 (49.3) | |
| Twin | 8 (1.3) | 2 (0.8) | 6 (1.7) | 0.30 |
| Type of feeding at hospital discharge | ||||
| Exclusive breastfeeding | 360 (60.2) | 156 (59.8) | 204 (60.5) | 0.67 |
| Mixed | 130 (21.7) | 54 (20.7) | 76 (22.6) | |
| Infant formula | 108 (18.1) | 51 (19.5) | 57 (16.9) | |
| Neonatology admission | 40 (6.5) | 23 (8.7) | 17 (4.9) | 0.06 |
| Jaundice | 10 (1.6) | 7 (2.6) | 3 (0.9) | 0.08 |
| Respiratory distress | 9 (1.5) | 5 (1.9) | 4 (1.1) | 0.44 |
| Low weight | 1 (0.2) | 1 (0.4) | 0 (0.0) | 0.25 |
| Prematurity | 4 (0.7) | 3 (1.1) | 1 (0.3) | 0.19 |
| SARS-CoV-2 antibodies | ||||
| IgG | 11 (1.9) | 6 (2.4) | 5 (1.5) | 0.43 |
| IgM | 2 (0.3 | 2 (0.8) | 0 (0.0) | 0.10 |