Table 2 Temporal trends in rates of twin, and triplet and higher-order (triplet+) multiple live births in Canada (excluding Ontario) and the United States, 1991–2009
Time period | Canada (excluding Ontario) | United States | ||||
|---|---|---|---|---|---|---|
Change in rate between first and last year of interval | P-value* | Change in rate between first and last year of interval | P-value* | |||
Absolute change in rate (95% CI)† | Relative change in rate (95% CI) | Absolute change in rate (95% CI)† | Relative change in rate (95% CI) | |||
Twins | ||||||
1991–2004 | 8.3 (7.4 to 9.2) | 41% (36% to 47%) | <0.0001 | 9.1 (8.9 to 9.3) | 39% (38% to 41%) | <0.0001 |
2004–2007 | 1.2 (0.2 to 2.2) | 4% (1% to 8%) | 0.0005 | 0 (-0.2 to 0.3) | 0% (-1% to 1%) | 0.81 |
2007–2009 | 1.9 (0.9 to 2.9) | 6% (3% to 10%) | 0.0001 | 1.0 (0.8 to 1.3) | 3% (2% to 4%) | <0.0001 |
Triplet+ | ||||||
1991–1998 | 45.0 (29.0 to 61.1) | 86% (50% to 132%) | <0.0001 | 112.1 (106.9 to 117.2) | 138% (128% to 148%) | <0.0001 |
1998–2003 | 13.9 (-5.8 to 33.5) | 14% (-5% to 38%) | 0.04 | -6.1 (-12.1 to -0.1) | -3% (-6% to 0%) | 0.13 |
2003–2007 | -33.5 (-51.9 to -15.1) | -30% (-43% to -15%) | <0.0001 | -38.5 (-44.0 to -32.9) | -21% (-23% to -18%) | <0.0001 |
2007–2009 | 5.9 (-10.3 to 22.1) | 6% (-12% to 32%) | 0.49 | 4.6 (-0.7 to 9.8) | 3% (0% to 7%) | 0.09 |