Table 2.
Basic conditions of the 2 groups.
| Variable | Number of studies | RR (95% CI) | I2 | Effects models | P value |
| Age | 18 | −0.16 (−0.38–0.07) | 37 | Fixed effects models | .18 |
| Height | 21 | −0.80 (−0.28–0.26) | 37 | Fixed effects models | .94 |
| Weight | 21 | −0.41 (−1.51–0.69) | 51 | Random effects models | .47 |
| BMI | 7 | 0.01 (−0.16–0.18) | 1 | Fixed effects models | .92 |
| Maternal systolic BP | 8 | 0.02 (−2.00–2.05) | 0 | Fixed effects models | .98 |
| Maternal diastolic BP | 4 | −0.94 (−2.84–0.96) | 0 | Fixed effects models | .33 |
| Maternal heart rate | 4 | −1.39 (−3.97–1.18) | 29 | Fixed effects models | .29 |
| Cervical dilation at initiation of analgesia | 20 | −0.03 (−0.10–0.04) | 55 | Random effects models | .43 |
| Oxytocin infusion | 5 | 1.34 (0.83–2.15) | 30 | Fixed effects models | .23 |
| Gestational age | 18 | 0.02 (−0.11–0.15) | 60 | Random effects models | .75 |
BMI = body mass index, BP = blood pressure, CI = confidence interval, RR = risk ratios.