| 95% Conf. Int./ | |||
| Rate/100,000 (n) | Rate/100,000 (n) | Significance | |
| Weeks | 5 States | Other U.S. | |
| 17 - 32 weeks | |||
| 2010 | 441.66 (38) | 502.32 (296) | |
| 2011 | 539.21 (46) | 516.84 (296) | |
| % Ch Rate | 22.09% | 2.89% | |
| 33 - 36 weeks | |||
| 2010 | 358.92 (128) | 441.81 (942) | |
| 2011 | 376.06 (129) | 440.72 (909) | |
| % Ch Rate | 4.78% | −0.25% | |
| 37 - 40 weeks | |||
| 2010 | 110.57 (377) | 165.31 (2729) | |
| 2011 | 128.32 (435) | 159.48 (2612) | |
| % Ch Rate | 16.05% | −3.52% | 0.015 - 0.257 (p < 0.03) |
| 41 - 47 weeks | |||
| 2010 | 87.50 (57) | 136.78 (411) | |
| 2011 | 96.01 (62) | 119.10 (363) | |
| % Ch Rate | 9.73% | −12.93% |