Table 2. Rates, RRs, and aRRs for Use of ART by Prepregnancy BMI Category.
| Prepregnancy BMI | Total births, No. | ART births, No. (per 1000) | Complete case analysis | Multiple imputationa | ||
|---|---|---|---|---|---|---|
| RR (95% CI) | aRR (95% CI)b | RR (95% CI) | aRR (95% CI)b | |||
| Underweight | 22 396 | 495 (22.1) | 0.75 (0.69-0.82) | 0.92 (0.84-1.00) | 0.80 (0.73-0.88) | 0.93 (0.85-1.02) |
| Normal | 231 583 | 6823 (29.5) | 1 [Reference] | 1 [Reference] | 1 [Reference] | 1 [Reference] |
| Overweight | 83 887 | 2570 (30.6) | 1.04 (0.99-1.09) | 1.09 (1.04-1.14) | 1.04 (0.99-1.08) | 1.09 (1.05-1.14) |
| Obesity class I | 33 263 | 1054 (31.7) | 1.08 (1.01-1.15) | 1.25 (1.18-1.33) | 1.07 (1.00-1.14) | 1.23 (1.16-1.31) |
| Obesity class II | 13 308 | 426 (32.0) | 1.09 (0.99-1.20) | 1.30 (1.18-1.43) | 1.07 (0.97-1.18) | 1.26 (1.15-1.38) |
| Obesity class III | 7609 | 155 (20.4) | 0.69 (0.59-0.81) | 0.82 (0.71-0.96) | 0.77 (0.65-0.90) | 0.91 (0.78-1.06) |
Abbreviations: aRR, adjusted rate ratio; ART, assisted reproductive technology; BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); RR, rate ratio.
a
Results pooled from 20 imputed data sets.
b
Adjusted for maternal height, age, smoking status, parity, and fiscal year.