Table 3.

Differential Effects of Low‐Dose Aspirin on Risk of PE or Related Complications Depending on Whether the Therapy Was Initiated Before or After 16 Gestational Weeks

Outcome	Trials, No.	Patients, No.	Events, No.		Meta‐Analysis		I 2, %	Subgroup Analysis P Value
			Aspirin	Placebo	OR (95% CI)	P Value
PE	21	4406	11.1	17.1	0.57 (0.40–0.80)	.001	61
≤16	7	1165	14.2	28.3	0.37 (0.27–0.50)	<.00001	44	.05
>16	14	3241	10.0	13.0	0.77 (0.62–0.97)	.02	45
IUGR	10	1540	11.7	20.4	0.50 (0.38–0.67)	<.00001	0
≤16	6	1044	10.5	20.8	0.4 (0.30–0.61)	<.00001	0	.003
>16	4	496	14.4	19.8	0.67 (0.41–1.08)	.10	0
Preterm birth	12	2470	15.9	23.3	0.62 (0.50–0.76)	<.00001	42
≤16	3	726	8.7	21.5	0.32 (0.20–0.51)	<.00001	0	.08
>16	9	1744	18.9	24.1	0.74 (0.58–0.93)	.01	6
Perinatal death	14	3785	2.6	3.4	0.76 (0.53–1.10)	.15	0
≤16	3	784	1.3	1.8	0.73 (0.24–2.21)	.58	12	.15
>16	11	3001	3.0	3.8	0.76 (0.52–1.13)	.18	0
Cesarean section	13	2570	35.4	32.7	1.12 (0.94–1.32)	.20	26
≤16	4	693	21.2	24.4	0.84 (0.59–1.20)	.33	0	.83
>16	9	1877	40.5	35.9	1.21 (1.00–1.47)	.05	29

Abbreviations: CI, confidence interval; IUGR, intrauterine growth restriction; OR, odds ratio; PE, preeclampsia. The following complications were not meta‐analyzed because of limited numbers of randomized controlled trials (RCTs) reporting the relevant outcomes data: postpartum hemorrhage=only one RCT; spontaneous abortion=two RCTs; severe preeclampsia=two RCTs; antepartum hemorrhage=one RCT; transfer to neonatal intensive care unit=one RCT; and placental abruption, neonatal intraventricular hemorrhage, or neonatal Apgar score=no RCTs.