Antioxidants for female subfertility.

EDITORIAL NOTE

M.G. Showell, R. Mackenzie‐Proctor, V. Jordan, and R.J. Hart, “Antioxidants for Female Subfertility,” Cochrane Database of Systematic Reviews, no. 8 (2020): CD007807, https://doi.org/10.1002/14651858.CD007807.pub4 This Editorial Note is for the above article, published online on August 27, 2020, in Cochrane Library (cochranelibrary.com), and has been issued by the Publisher, John Wiley & Sons Ltd, in agreement with Cochrane. The Editorial note has been agreed due to concerns discovered by the Cochrane managing editor regarding the retraction of six studies in the Review (Badawy et al. 2006, 10.1016/j.fertnstert.2006.02.097; El Refaeey et al. 2014, 10.1016/j.rbmo.2014.03.011; El Sharkwy & Abd El Aziz 2019a, https://doi.org/10.1002/ijgo.12902; Gerli et al. 2007, https://doi.org/10.26355/eurrev_202309_33752, full text: https://europepmc.org/article/MED/18074942; Ismail et al. 2014, http://dx.doi.org/10.1016/j.ejogrb.2014.06.008; Hashemi et al. 2017, https://doi.org/10.1080/14767058.2017.1372413). In addition, expressions of concern have been published for two studies (Jamilian et al. 2018, https://doi.org/10.1007/s12011-017-1236-3; Zadeh Modarres 2018, https://doi.org/10.1007/s12011-017-1148-2). The retracted studies will be moved to the Excluded Studies table, and their impact on the review findings will be investigated and acted on accordingly in a future update. Initial checks indicate that removal of the six retracted studies did not make an appreciable difference to the results. Likewise, the studies for which Expressions of Concern were issued will be moved to the Awaiting classification table; they did not report any review outcomes, so removal will have no impact on the review findings.

BACKGROUND

A couple may be considered to have fertility problems if they have been trying to conceive for over a year with no success. This may affect up to a quarter of all couples planning a child. It is estimated that for 40% to 50% of couples, subfertility may result from factors affecting women. Antioxidants are thought to reduce the oxidative stress brought on by these conditions. Currently, limited evidence suggests that antioxidants improve fertility, and trials have explored this area with varied results. This review assesses the evidence for the effectiveness of different antioxidants in female subfertility.

OBJECTIVES

To determine whether supplementary oral antioxidants compared with placebo, no treatment/standard treatment or another antioxidant improve fertility outcomes for subfertile women.

SEARCH METHODS

We searched the following databases (from their inception to September 2019), with no language or date restriction: Cochrane Gynaecology and Fertility Group (CGFG) specialised register, CENTRAL, MEDLINE, Embase, PsycINFO, CINAHL and AMED. We checked reference lists of relevant studies and searched the trial registers.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that compared any type, dose or combination of oral antioxidant supplement with placebo, no treatment or treatment with another antioxidant, among women attending a reproductive clinic. We excluded trials comparing antioxidants with fertility drugs alone and trials that only included fertile women attending a fertility clinic because of male partner infertility.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. The primary review outcome was live birth; secondary outcomes included clinical pregnancy rates and adverse events.

MAIN RESULTS

We included 63 trials involving 7760 women. Investigators compared oral antioxidants, including: combinations of antioxidants, N-acetylcysteine, melatonin, L-arginine, myo-inositol, carnitine, selenium, vitamin E, vitamin B complex, vitamin C, vitamin D+calcium, CoQ10, and omega-3-polyunsaturated fatty acids versus placebo, no treatment/standard treatment or another antioxidant. Only 27 of the 63 included trials reported funding sources. Due to the very low-quality of the evidence we are uncertain whether antioxidants improve live birth rate compared with placebo or no treatment/standard treatment (odds ratio (OR) 1.81, 95% confidence interval (CI) 1.36 to 2.43; P < 0.001, I = 29%; 13 RCTs, 1227 women). This suggests that among subfertile women with an expected live birth rate of 19%, the rate among women using antioxidants would be between 24% and 36%. Low-quality evidence suggests that antioxidants may improve clinical pregnancy rate compared with placebo or no treatment/standard treatment (OR 1.65, 95% CI 1.43 to 1.89; P < 0.001, I = 63%; 35 RCTs, 5165 women). This suggests that among subfertile women with an expected clinical pregnancy rate of 19%, the rate among women using antioxidants would be between 25% and 30%. Heterogeneity was moderately high. Overall 28 trials reported on various adverse events in the meta-analysis. The evidence suggests that the use of antioxidants makes no difference between the groups in rates of miscarriage (OR 1.13, 95% CI 0.82 to 1.55; P = 0.46, I = 0%; 24 RCTs, 3229 women; low-quality evidence). There was also no evidence of a difference between the groups in rates of multiple pregnancy (OR 1.00, 95% CI 0.63 to 1.56; P = 0.99, I = 0%; 9 RCTs, 1886 women; low-quality evidence). There was also no evidence of a difference between the groups in rates of gastrointestinal disturbances (OR 1.55, 95% CI 0.47 to 5.10; P = 0.47, I = 0%; 3 RCTs, 343 women; low-quality evidence). Low-quality evidence showed that there was also no difference between the groups in rates of ectopic pregnancy (OR 1.40, 95% CI 0.27 to 7.20; P = 0.69, I = 0%; 4 RCTs, 404 women). In the antioxidant versus antioxidant comparison, low-quality evidence shows no difference in a lower dose of melatonin being associated with an increased live-birth rate compared with higher-dose melatonin (OR 0.94, 95% CI 0.41 to 2.15; P = 0.89, I = 0%; 2 RCTs, 140 women). This suggests that among subfertile women with an expected live-birth rate of 24%, the rate among women using a lower dose of melatonin compared to a higher dose would be between 12% and 40%. Similarly with clinical pregnancy, there was no evidence of a difference between the groups in rates between a lower and a higher dose of melatonin (OR 0.94, 95% CI 0.41 to 2.15; P = 0.89, I = 0%; 2 RCTs, 140 women). Three trials reported on miscarriage in the antioxidant versus antioxidant comparison (two used doses of melatonin and one compared N-acetylcysteine versus L-carnitine). There were no miscarriages in either melatonin trial. Multiple pregnancy and gastrointestinal disturbances were not reported, and ectopic pregnancy was reported by only one trial, with no events. The study comparing N-acetylcysteine with L-carnitine did not report live birth rate. Very low-quality evidence shows no evidence of a difference in clinical pregnancy (OR 0.81, 95% CI 0.33 to 2.00; 1 RCT, 164 women; low-quality evidence). Low quality evidence shows no difference in miscarriage (OR 1.54, 95% CI 0.42 to 5.67; 1 RCT, 164 women; low-quality evidence). The study did not report multiple pregnancy, gastrointestinal disturbances or ectopic pregnancy. The overall quality of evidence was limited by serious risk of bias associated with poor reporting of methods, imprecision and inconsistency.

AUTHORS' CONCLUSIONS: In this review, there was low- to very low-quality evidence to show that taking an antioxidant may benefit subfertile women. Overall, there is no evidence of increased risk of miscarriage, multiple births, gastrointestinal effects or ectopic pregnancies, but evidence was of very low quality. At this time, there is limited evidence in support of supplemental oral antioxidants for subfertile women.