Comparison 3. Antiplatelet agents versus placebo/no treatment for primary prevention (primary outcomes, subgroups by use of placebo).

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Pre‐eclampsia	60	36871	Risk Ratio (M‐H, Fixed, 95% CI)	0.82 [0.77, 0.88]
1.1 Placebo (IPD)	24	31090	Risk Ratio (M‐H, Fixed, 95% CI)	0.89 [0.83, 0.96]
1.2 Placebo (AD)	22	3878	Risk Ratio (M‐H, Fixed, 95% CI)	0.57 [0.47, 0.70]
1.3 No placebo (IPD)	7	1127	Risk Ratio (M‐H, Fixed, 95% CI)	0.64 [0.37, 1.12]
1.4 No placebo (AD)	7	776	Risk Ratio (M‐H, Fixed, 95% CI)	0.53 [0.41, 0.69]
2 Fetal death, neonatal death, or death before hospital discharge	52	35391	Risk Ratio (M‐H, Fixed, 95% CI)	0.85 [0.76, 0.95]
2.1 Placebo (IPD)	24	31090	Risk Ratio (M‐H, Fixed, 95% CI)	0.90 [0.79, 1.02]
2.2 Placebo (AD)	14	2652	Risk Ratio (M‐H, Fixed, 95% CI)	0.70 [0.47, 1.05]
2.3 No placebo (IPD)	7	1127	Risk Ratio (M‐H, Fixed, 95% CI)	0.75 [0.43, 1.30]
2.4 No placebo (AD)	6	452	Risk Ratio (M‐H, Fixed, 95% CI)	0.42 [0.23, 0.80]
2.5 Unclear/unspecified (AD)	1	70	Risk Ratio (M‐H, Fixed, 95% CI)	0.40 [0.04, 3.62]
3 Preterm birth	47	35212	Risk Ratio (M‐H, Fixed, 95% CI)	0.90 [0.86, 0.94]
3.1 Placebo (IPD)	24	31070	Risk Ratio (M‐H, Fixed, 95% CI)	0.93 [0.89, 0.98]
3.2 Placebo (AD)	11	2423	Risk Ratio (M‐H, Fixed, 95% CI)	0.57 [0.47, 0.69]
3.3 No placebo (IPD)	7	1127	Risk Ratio (M‐H, Fixed, 95% CI)	0.90 [0.72, 1.14]
3.4 No placebo (AD)	5	592	Risk Ratio (M‐H, Fixed, 95% CI)	0.79 [0.58, 1.08]
4 Small‐for‐gestational age	49	35606	Risk Ratio (M‐H, Fixed, 95% CI)	0.84 [0.77, 0.93]
4.1 Placebo (IPD)	24	31090	Risk Ratio (M‐H, Fixed, 95% CI)	0.90 [0.81, 1.00]
4.2 Placebo (AD)	13	2885	Risk Ratio (M‐H, Fixed, 95% CI)	0.72 [0.58, 0.90]
4.3 No Placebo (IPD)	7	1127	Risk Ratio (M‐H, Fixed, 95% CI)	0.91 [0.52, 1.58]
4.4 No placebo (AD)	5	504	Risk Ratio (M‐H, Fixed, 95% CI)	0.52 [0.33, 0.82]