sPTD | Initiation of folic acid | Â | Unadjusted | Adjusted1 | Adjusted2 | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|
 | supplementation | n | HR | (CI) | p | HR | (CI) | p | HR | (CI) | p |
 | No | 919 | 1 |  |  | 1 |  |  | 1 |  |  |
All | 0-8 w preconceptional | 281 | 0.94 | (0.82–1.07) | 0.36 | 1.01 | (0.88–1.16) | 0.91 | 1.02 | (0.88–1.17) | 0.82 |
 | >8 w preconceptional | 428 | 1.14 | (1.02–1.28) | 0.02 | 1.19 | (1.05–1.34) | 0.01 | 1.19 | (1.04–1.35) | 0.01 |
 | No | 139 | 1 |  |  | 1 |  |  | 1 |  |  |
Early | 0-8 w preconceptional | 46 | 1.02 | (0.73–1.42) | 0.92 | 1.15 | (0.82–1.62) | 0.43 | 1.10 | (0.77–1.57) | 0.59 |
 | >8 w preconceptional | 79 | 1.39 | (1.06–1.84) | 0.02 | 1.53 | (1.14–2.04) | 0.004 | 1.45 | (1.05–1.99) | 0.02 |
 | No | 780 | 1 |  |  | 1 |  |  | 1 |  |  |
Late | 0-8 w preconceptional | 235 | 0.93 | (0.8–1.07) | 0.30 | 0.98 | (0.85–1.14) | 0.83 | 1.00 | (0.86–1.17) | 0.98 |
 | >8 w preconceptional | 349 | 1.10 | (0.97–1.25) | 0.14 | 1.13 | (0.99–1.29) | 0.07 | 1.14 | (0.99–1.32) | 0.07 |