Comparison 4. Timing subgroups.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Preterm birth (< 37 weeks)	26	10304	Risk Ratio (M‐H, Fixed, 95% CI)	0.89 [0.81, 0.97]
1.1 ≤ 20 weeks GA start	12	6563	Risk Ratio (M‐H, Fixed, 95% CI)	0.85 [0.76, 0.95]
1.2 > 20 weeks GA start	13	3693	Risk Ratio (M‐H, Fixed, 95% CI)	1.01 [0.82, 1.23]
1.3 Mixed	1	48	Risk Ratio (M‐H, Fixed, 95% CI)	0.11 [0.01, 2.22]
2 Early preterm birth (< 34 weeks)	9	5204	Risk Ratio (M‐H, Fixed, 95% CI)	0.58 [0.44, 0.77]
2.1 ≤ 20 weeks GA start	8	5090	Risk Ratio (M‐H, Fixed, 95% CI)	0.56 [0.43, 0.75]
2.2 > 20 weeks GA start	1	114	Risk Ratio (M‐H, Fixed, 95% CI)	4.83 [0.24, 98.44]
3 Prolonged gestation (> 42 weeks)	6	5141	Risk Ratio (M‐H, Fixed, 95% CI)	1.61 [1.11, 2.33]
3.1 ≤ 20 weeks GA start	5	4608	Risk Ratio (M‐H, Fixed, 95% CI)	2.35 [1.29, 4.28]
3.2 > 20 weeks GA start	1	533	Risk Ratio (M‐H, Fixed, 95% CI)	1.19 [0.73, 1.93]
4 Pre‐eclampsia (hypertension with proteinuria)	20	8306	Risk Ratio (M‐H, Fixed, 95% CI)	0.84 [0.69, 1.01]
4.1 ≤ 20 weeks GA start	13	6296	Risk Ratio (M‐H, Fixed, 95% CI)	0.92 [0.74, 1.15]
4.2 > 20 weeks GA start	6	1883	Risk Ratio (M‐H, Fixed, 95% CI)	0.79 [0.53, 1.18]
4.3 Not reported	1	127	Risk Ratio (M‐H, Fixed, 95% CI)	0.07 [0.01, 0.54]
5 Caesarean section	28	8481	Risk Ratio (M‐H, Fixed, 95% CI)	0.97 [0.91, 1.03]
5.1 ≤ 20 weeks GA start	13	4995	Risk Ratio (M‐H, Fixed, 95% CI)	0.97 [0.88, 1.07]
5.2 > 20 weeks GA start	14	2617	Risk Ratio (M‐H, Fixed, 95% CI)	0.98 [0.87, 1.10]
5.3 Mixed	1	869	Risk Ratio (M‐H, Fixed, 95% CI)	0.95 [0.83, 1.08]
6 Length of gestation (days)	43	12517	Mean Difference (IV, Random, 95% CI)	1.67 [0.95, 2.39]
6.1 ≤ 20 weeks GA start	23	9396	Mean Difference (IV, Random, 95% CI)	1.99 [1.08, 2.90]
6.2 > 20 weeks GA start	20	3121	Mean Difference (IV, Random, 95% CI)	1.18 [‐0.05, 2.40]
7 Perinatal death	10	7416	Risk Ratio (M‐H, Fixed, 95% CI)	0.75 [0.54, 1.03]
7.1 ≤ 20 weeks GA start	6	5815	Risk Ratio (M‐H, Fixed, 95% CI)	0.72 [0.49, 1.07]
7.2 > 20 weeks GA start	4	1601	Risk Ratio (M‐H, Fixed, 95% CI)	0.79 [0.46, 1.38]
8 Stillbirth	16	7880	Risk Ratio (M‐H, Fixed, 95% CI)	0.94 [0.62, 1.42]
8.1 ≤ 20 weeks GA start	8	5537	Risk Ratio (M‐H, Fixed, 95% CI)	0.88 [0.52, 1.48]
8.2 > 20 weeks GA start	7	2295	Risk Ratio (M‐H, Fixed, 95% CI)	1.02 [0.50, 2.07]
8.3 Mixed	1	48	Risk Ratio (M‐H, Fixed, 95% CI)	1.69 [0.07, 39.30]
9 Neonatal death	9	7448	Risk Ratio (M‐H, Fixed, 95% CI)	0.61 [0.34, 1.11]
9.1 ≤ 20 weeks GA start	6	5415	Risk Ratio (M‐H, Fixed, 95% CI)	0.60 [0.26, 1.36]
9.2 > 20 weeks GA start	3	2033	Risk Ratio (M‐H, Fixed, 95% CI)	0.62 [0.26, 1.49]
10 Low birthweight (< 2500 g)	15	8449	Risk Ratio (M‐H, Fixed, 95% CI)	0.90 [0.82, 0.99]
10.1 ≤ 20 weeks GA start	9	6553	Risk Ratio (M‐H, Fixed, 95% CI)	0.88 [0.79, 0.97]
10.2 > 20 weeks GA start	6	1896	Risk Ratio (M‐H, Fixed, 95% CI)	1.02 [0.81, 1.28]
11 Small‐for‐gestational age/IUGR	8	6907	Risk Ratio (M‐H, Fixed, 95% CI)	1.01 [0.90, 1.13]
11.1 ≤ 20 weeks GA start	5	5643	Risk Ratio (M‐H, Fixed, 95% CI)	1.00 [0.88, 1.14]
11.2 > 20 weeks GA start	3	1264	Risk Ratio (M‐H, Fixed, 95% CI)	1.03 [0.79, 1.34]
12 Birthweight (g)	43	11584	Mean Difference (IV, Random, 95% CI)	75.69 [37.84, 113.55]
12.1 ≤ 20 weeks GA start	25	7802	Mean Difference (IV, Random, 95% CI)	83.26 [44.09, 122.43]
12.2 > 20 weeks GA start	17	3747	Mean Difference (IV, Random, 95% CI)	42.96 [‐34.14, 120.06]
12.3 Not reported	1	35	Mean Difference (IV, Random, 95% CI)	200.0 [‐205.07, 605.07]