Table 3.
Rates and Pooled Estimates for Primary Outcome, Stratified Analyses, and Secondary Analyses
| Outcome | No. of studies |
Exposed % (n outcome/n exposed) |
Unexposed % (n outcome/n unexposed) |
Pooled Relative Risk |
95% CI | Heterogeneity | ||
|---|---|---|---|---|---|---|---|---|
| Cochran’s P value |
I2 | |||||||
| PTB <37 wks | 19 | 8.8% (582/6549) |
5.1% (71732/1415023) |
1.61 | 1.35–1.92 | 0.001 | 59.2% | |
| Stratified by study unexposed group |
||||||||
| No/unknown hx of dysplasia |
15 | 8.6% (473/5457) |
4.6% (54036/1172059) |
1.86 | 1.58–2.21 | 0.069 | 37.7% | |
| Hx of dysplasia | 4 | 10.0% (109/1092) |
7.2% (17696/242946) |
1.08 | 0.88–1.33 | 0.654 | 0.00% | |
| Stratified by Study Quality |
||||||||
| Lower | 12 | 10.3% (188/1833) |
4.1% (3627/89089) |
1.75 | 1.36–2.26 | 0.057 | 42.8% | |
| Higher | 7 | 8.4% (394/4716) |
5.1% (68105/1325926) |
1.48 | 1.14–1.91 | 0.001 | 72.1% | |
| Spontaneous PTB<37 wks |
8 | 6.8% (147/2175) |
3.4% (11684/342097) |
1.60 | 0.99–2.55 | <0.001 | 73.6% | |
| Preterm PROM | 6 | 5.1% (108/2102) |
2.5% (7940/314891) |
2.37 | 1.64–3.44 | 0.094 | 46.9% | |
| PTB<34 wks | 5 | 2.9% (48/1670) |
2.3% (6053/267889) |
2.21 | 1.33–3.67 | 0.157 | 39.6% | |
| Perinatal mortality | 7 | 1.0% (19/1925) |
0.8% (2496/315118) |
1.63 | 0.95–2.80 | 0.911 | 0.00% | |
CI, confidence interval; PTB, preterm birth; hx, history; PROM, premature rupture of membranes.