Table 5. Multivariable associations of potential risk factors with preterm birth, low birth weight and macrosomia amongst singleton births following IVF.
| Characteristic | Categories | Multivariable Association with Preterm Birth; N = 24,096 in Analyses with n = 2,070 Cases of Preterm Birth | Multivariable Association with Low Birth Weight; N = 21,804 in Analyses with n = 2,100 Cases of Low Birth Weight | Multivariable Association with Low Birth Weight; N = 21,950 in Analyses with n = 2,246 Cases of Macrosomia | |||
| Odds Ratio (95%CI) | p-Value | Odds Ratio (95%CI) | p-Value | Odds Ratio (95%CI) | p-Value | ||
| Age, y | 18–34 | 1 | 0.12 | 1 | 0.04 | 1 | 0.01 |
| 35–37 | 0.90 (0.80–1.00) | 0.87 (0.78–0.97) | 1.14 (1.03–1.27) | ||||
| 38–39 | 0.87 (0.75–1.00) | 0.86 (0.74–0.99) | 1.09 (0.95–1.25) | ||||
| ≥40 | 0.93 (0.77–1.10) | 0.96 (0.80–1.15) | 1.25 (1.06–1.48) | ||||
| Duration of infertility, y | <1 | 1.05 (0.73–1.49) | 0.004 | 0.86 (0.58–1.25) | 0.01 | 0.81 (0.56–1.17) | 0.20 |
| 1–3 | 0.96 (0.86–1.07) | 0.90 (0.80–1.00) | 0.90 (0.81–0.99) | ||||
| 4–6 | 1 | 1 | 1 | ||||
| 7–9 | 1.17 (1.02–1.35) | 1.07 (0.93–1.24) | 1.02 (0.89–1.16) | ||||
| ≥9 | 1.25 (1.07–1.46) | 1.16 (1.00–1.36) | 0.93 (0.80–1.09) | ||||
| Cause | Unknown | 1 | <0.001 | 1 | 0.02 | 1 | 0.002 |
| Tubal only | 1.22 (1.06–1.41) | 1.12 (0.97–1.30) | 1.06 (0.91–1.22) | ||||
| Anovulatory only | 1.14 (0.95–1.37) | 1.19 (1.00–1.42 | 1.04 (0.86–1.25) | ||||
| Endometriosis only | 0.86 (0.65–1.14) | 1.04 (0.80–1.35) | 0.96 (0.73–1.25) | ||||
| Cervical only | 9.09 (2.01–41.13) | 15.62 (2.59–94.06) | 10.46 (1.46–74.85) | ||||
| Male only | 0.95 (0.83–1.09) | 1.02 (0.89–1.17) | 1.22 (1.07–1.39) | ||||
| Combination known causes | 1.19 (1.00–1.41) | 1.15 (0.97–1.36) | 0.92 (0.77–1.11) | ||||
| Previous unsuccessful IVF, number | 0 | 1 | 0.44 | 1 | 0.37 | 1 | 0.95 |
| 1 | 0.75 (0.50–1.15) | 0.85 (0.56–1.29) | 0.92 (0.77–1.10) | ||||
| 2 | 0.80 (0.50–1.30) | 0.82 (0.51–1.32) | 0.92 (0.61–1.38) | ||||
| ≥3 | 0.66 (0.40–1.11) | 0.63 (0.38–1.06) | 0.98 (0.61–1.58) | ||||
| Mutually exclusive categories of previous IVF and obstetric history | No previous IVF, 0 pregnancy | 1 | 0.11 | 1 | 0.004 | 1 | <0.001 |
| No previous IVF, at least 1 pregnancy, 0 live births | 1.15 (0.40–1.11) | 1.13 (1.00–1.27) | 1.23 (1.09–1.39) | ||||
| No previous IVF, at least 1 pregnancy, at least 1 live birth | 0.99 (0.84–1.16) | 0.83 (0.70–0.98) | 1.28 (1.11–1.49) | ||||
| Previous IVF, 0 pregnancy | 1.48 (0.95–2.30) | 1.54 (1.00–2.39) | 0.97 (0.63–1.49) | ||||
| Previous IVF, at least 1 pregnancy, 0 live birth | 1.30 (0.93–1.80) | 1.37 (0.99–1.91) | 1.02 (0.72–1.43) | ||||
| Previous IVF, at least 1 pregnancy, at least 1 live birth | 1.02 (0.55–1.38) | 0.89 (0.67–1.17) | 1.30 (1.03–1.63) | ||||
| Hormonal preparation | Antioestrogen | 1 | 0.11 | 1 | 0.77 | 1 | 0.86 |
| Gonadatrophin | 0.87 (0.55–1.39) | 1.18 (0.71–1.97) | 1.08 (0.64–1.83) | ||||
| Hormone replacement | 1.07 (0.63–1.82) | 1.24 (0.69–2.21) | 1.15 (0.64–2.07) | ||||
| Cycle number | 1 | 1 | 0.43 | 1 | 0.17 | 1 | 0.04 |
| 2 | 1.00 (0.89–1.13) | 0.96 (0.85–1.08) | 1.07 (0.96–1.20) | ||||
| ≥3 | 0.92 (0.81–1.05) | 0.89 (0.78–1.01) | 1.17 (1.04–1.31) | ||||
| Source of egg | Donor | 1 | <0.001 | 1 | <0.001 | 1 | 0.16 |
| Patient | 0.41 (0.26–0.64) | 0.42 (0.26–0.68) | 0.68 (0.39–1.17) | ||||
| Treatment type | IVF | 1 | 0.05 | 1 | 0.05 | 1 | 0.46 |
| IVF and ICSI | 0.89 (0.80–1.00) | 0.89 (0.80–1.00) | 0.96 (0.86–1.07) | ||||
Cycles included in analyses are from couples for whom data were complete on all variables and who experienced a singleton birth after IVF. For associations with low birth weight, those with macrosomia as an outcome are removed so that low birth weight is compared with normal birth weight, and similarly for macrosomia, those with low birth weight are removed so that macrosomia is compared with normal birth weight. The results are with mutual adjustment for all variables in the first column. In addition, for preterm birth, results are adjusted for mean birth weight and for low birth weight and macrosomia for mean gestational age. p-Values are likelihood ratio tests of null hypothesis that the odds are the same for each category (i.e., they do not assume linearity).