Pregnancy outcomes for women admitted to UK hospitals with SARS-CoV-2 related symptoms during periods in which the original wildtype, alpha variant, and delta variant were dominant
| Pregnancy outcomes | Wildtype period (n=1387) | Alpha period (n=1613) | Delta period (n=1436) | Alpha v wildtype period | |
| Odds ratio (95% CI) | Adjusted odds ratio (95% CI)* | ||||
| Pregnancy outcome known | 1356 (97.8) | 1545 (95.8) | 967 (67.3) | Not compared | Not compared |
| Pregnancy loss | 33 (2.4) | 26 (1.7) | 18 (1.9) | Not compared | Not compared |
| Birth | 1323 (95.4) | 1519 (94.2) | 949 (66.1) | Not compared | Not compared |
| Gestation at birth (weeks+days) | |||||
| <22 | 29 (2.2) | 18 (1.2) | 13 (1.3) | Not compared | Not compared |
| 22-27+6 | 13 (0.9) | 32 (2.1) | 20 (2.1) | 2.11 (1.07 to 4.18) | 2.38 (1.13 to 5.00) |
| 28-34+6 | 83 (6.2) | 119 (7.8) | 95 (9.8) | 1.30 (0.97 to 1.74) | 1.37 (1.00 to 1.87) |
| 34-36+6 | 148 (11.1) | 173 (11.4) | 149 (15.7) | 1.07 (0.85 to 1.34) | 1.06 (0.84 to 1.34) |
| 37 or more | 1065 (79.6) | 1180 (77.5) | 675 (69.8) | Reference | Reference |
| Missing data | 18 | 23 | 15 | — | — |
| Median (interquartile range)‡ | 39 (37-40) | 39 (37-40) | 39 (37-40) | −0.14 (−0.33 to 0.05) | −0.14 (−0.34 to 0.05) |
| Delivery expedited due to covid-19† | 85 (11.9) | 183 (12.7) | 174 (20.8) | 1.08 (0.82 to 1.42) | 1.06 (0.79 to 1.43) |
| Missing data | 610 | 79 | 111 | — | — |
| Mode of birth† | |||||
| Pre-labour caesarean | 416 (31.7) | 551 (36.9) | 376 (40.2) | 1.21 (1.02 to 1.45) | 1.17 (0.97 to 1.40) |
| Caesarean after labour onset | 200 (15.2) | 208 (13.9) | 102 (10.9) | 0.95 (0.76 to 1.20) | 0.91 (0.72 to 1.15) |
| Operative vaginal | 147 (11.2) | 135 (9.0) | 82 (8.8) | 0.84 (0.65 to 1.09) | 0.81 (0.62 to 1.06) |
| Unassisted vaginal | 549 (41.8) | 600 (40.2) | 375 (40.1) | Reference | Reference |
| Missing data | 11 | 25 | 14 | — | — |
Data are number (%) of women. Reference=reference group against which other categories were compared; wildtype to delta comparison purposely not undertaken owing to differing availability of pregnancy outcome data.
*Adjusted for age, ethnic origin, body mass index, employment, and presence of one or more pre-existing relevant medical comorbidity.
†Excluding pregnancy loss from denominator.
‡Quantile (median) regression using bootstrap sampling.