1. Data for undefined or biochemical pregnancy.

Undefined or biochemical pregnancy	Antioxidant		Control		Peto OR [CI]
Antioxidant(s) versus placebo or no treatment
Combined antioxidants	Events	Total	Events	Total
Galatioto 2008	1	20	0	22	8.17 [0.16 to 413.39]
Gopinath 2013	13	92	2	46	2.72 [0.88 to 8.46]
Arginine
Pryor 1978	2	35	2	29	0.82 [0.11 to 6.16]
Carnitines	25	154	3	145
Sigman 2006	1	12	1	9	0.74 [0.04 to 13.02]
Peivandi 2010	3	15	0	15	8.57 [0.82 to 89.45]
Lenzi 2004	4	30	0	26	7.20 [0.95 to 54.34]
Lenzi 2003	6	43	0	43	8.37 [1.61 to 43.58]
Cavallini 2004	9	39	1	47	7.50 [2.01 to 27.98]
Coenzyme Q10	6	136	3	136
Safarinejad 2009a	0	106	0	106	Not estimable
Balercia 2009	6	30	3	30	2.16 [0.53 to 8.82]
Nadjarzadeh 2011	0	23	0	24	Not estimable
Vitamin C + Vitamin E
Rolf 1999	0	15	0	16	Not estimable
Vitamin E
Ener 2016	5	28	5	28	1.00 [0.26 to 3.88]
Head‐to‐head antioxidant(s)	Events	Total	Events	Total
L‐acetyl carnitine + L‐carnitine vs Vitamin E + Vitamin C
Li 2005	10	85	2	53	2.72 [0.81 to 9.14]
L‐carnitine + Vitamin E versus Vitamin E
Wang 2010	21	68	3	67	6.01 [2.49 to 14.47]