Samuel Santos-Ribeiro

Scientific Coordinator and Senior Gynecologist, IVI RMA Lisbon
  • IVI RMA Lisbon
  • Portugal

About Samuel Santos-Ribeiro

I obtained my medical degree from Nova Medical School (Lisbon), concluding my training in Obstetrics/Gynaecology at Hospital Santa Maria (Lisbon). I performed the Clinical Scholars Research Training (Harvard Medical School) and a research programme at Universitair Ziekenhuis Brussel (Brussels) with my Ph.D. thesis focusing primarily on the optimisation of endometrial receptivity during ART. I am currently the Scientific Coordinator at IVIRMA Lisbon and an Invited Professor at the Faculty of Medicine of the University of Lisbon. The primary focus of my ongoing research is on the optimization of endometrial receptivity and ART safety.

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Recent Comments

Replying to Pamela Rossi

HI! My name is Pamela Rossi, I am a psychologist  from Argentina and i´ve got some questions to the authors of this article. Can you bring me a mail adress to contact them? Thaks so much. Best Regards.

The email address of the corresponding author is available by clicking on the full-text link and then clicking on the envelope symbol near the corresponding author's name.

Replying to Christopher De Jonge

Is this commentary available as a pdf? Also, how would it be referenced?

Thank you,

Christopher De Jonge, Ph.D., HCLD

This commentary is only available in the F&S dialog platform for now. Nonetheless, it is still citable indeed, using the usual format of author name, title, Fertil Steril, year and then the internet link.

Replying to Parviz Gharagozloo

Yet another flawed antioxidant trial; a plea for rigorous evaluation of antioxidant therapy for male infertility involving oxidative stress

The role of oxidative stress in the aetiology of male infertility has been appreciated since the 1920’s when it was demonstrated that depriving rats of natural vitamin E, the major antioxidant vitamin, generated testicular degeneration and infertility (1,2). Subsequently, a great deal of research has been conducted on the role of oxidative stress in male infertility and there is now a general consensus that reactive oxygen species play a significant role in the creation of defective sperm function and the induction of sperm DNA damage (3-6). Recent papers clearly reveal roles for oxidative stress in a variety of clinical situations including the aetiology of non-obstructive azoospermia (7), defective sperm quality in teratozoospermia (8), the origins of sperm DNA damage (9), the toxic impact of parabens (10) and the pathophysiology of varicocele (11). If oxidative stress is such an important cause of male infertility, then surely antioxidant therapy should be part of the cure (12).


In animal models, this is certainly the case. For example, the GPx5 (glutathione peroxidase 5) knockout mouse suffers from localized oxidative stress in the epididymis (13). As a consequence of this stress, the spermatozoa exhibit clear signs of oxidative damage including impaired DNA compaction and high levels of oxidative DNA damage. When Gpx5-deficient males were mated to normal females, the presence of oxidatively damaged spermatozoa was associated with higher incidences of miscarriage and developmental defects in the offspring. However, when such GPx5-/- males were treated with a carefully engineered antioxidant formulation, oxidative DNA damage in the spermatozoa was found to return to control levels (14). Similarly, treatment with the same antioxidant formulation almost completely restored the fertility of mice rendered infertile by a transient testicular hyperthermia (14). Indeed there is a wealth of animal literature demonstrating that antioxidants can restore fertility and testicular function in animals treated with a wide range of factors capable of causing oxidative stress in the male reproductive tract including cadmium (15), phthalate esters (16), lead, organophosphate pesticides (17), induced diabetes (18), acrylamide exposure (19), mental stress (20) and so on.


Against such a background of supportive data in animal models, it is perhaps surprising that extension of these studies into the clinical domain has not provided evidence of a clear therapeutic benefit of antioxidant administration in man. Several meta-analyses addressing this question have been performed.  Recent systematic Cochrane analyses, for example, (21,22) concluded that there was low quality evidence for a positive effect on clinical pregnancy and live birth rates but emphasized the flaws in existing studies based on ‘on serious risk of bias due to poor reporting of methods of randomisation, failure to report on the clinical outcomes, live birth rate and clinical pregnancy, often unclear or even high attrition, and also imprecision due to often low event rates and small overall sample sizes’. Both Cochrane analyses called for large, well-designed, randomised placebo-controlled trials to clarify these results. It was, therefore, with interest that we encountered the paper in Fertility and Sterility by Steiner et al. (23) reporting the results of a large randomized placebo-controlled trial of antioxidant therapy in male infertility. While this study has many excellent features, disappointingly, it turned out to be as fundamentally flawed as its predecessors.  


How is it possible to design a study determining the efficacy of antioxidant therapy when no attempt is made to determine levels of oxidative stress in the patients before or after the administration of treatment? This makes no sense. It is like giving insulin to everyone who comes into hospital in a coma. Some will improve, some will continue to deteriorate and, overall, any therapeutic benefit will be lost in the noise. The males selected in this study exhibited at least one abnormal semen parameter in the previous 6 months [sperm concentration <15 million/mL (oligospermia), total motility <40% (asthenospermia), normal morphology <4% (teratospermia), or DNA fragmentation >25%]. Naturally, there are many different reasons for males to exhibit such defects and only in a proportion will this be due to oxidative stress. The authors clearly recognise this fundamental defect in their study but justify the omission of oxidative stress measurements on the basis that the random allocation of antioxidant treatment to infertile patients, irrespective of need, represents the current standard of clinical practice. While this statement is clearly correct, surely we should be encouraging higher standards of clinical implementation, rather than just reinforcing the status quo.


Similar arguments could be directed towards the DNA damage component of the study which focused on the vulnerability of the chromatin to low pH (the sperm chromatin structure assay) rather than the formation of oxidative base adducts (8-Oxo-2'-deoxyguanosine) which has been recently shown to be rather a common trait of infertile male patients (24) and to concern specific paternal chromosomal regions that could be linked to developmental defects in the offspring (25).


The other major factor that needs to be considered is the choice of formulation used in the trial. There are numerous male fertility supplements available in the market worldwide, greatly varying by both the nature of antioxidants incorporated into the formulation and the doses used. So why this particular composition? The authors justify the ingredients and doses used because similar ones had been previously evaluated individually in clinical trials and demonstrated some benefit. However, other studies have demonstrated serious concerns with either the isoformic nature of the ingredients or high doses of the individual ingredients used (14). As an example, high doses of antioxidants such as vitamin C or Zinc, especially in the situation where oxidative stress is absent or minimal, can lead to reductive stress (12) causing sperm DNA decondensation (26-28). Reductive stress arising from over-supplementation can therefore be just as damaging to spermatozoa as oxidative stress and should be avoided. This is another reason why understanding a patient’s oxidative stress status is important to the success of a clinical trial, so patients with low or no oxidative stress can be excluded from the trial.


The field desperately needs to support large scale placebo-controlled studies of the type conducted by Steiner et al (23). However, we shall learn nothing if we do not select the patients on the basis of criteria reflecting levels of oxidative stress in the male reproductive tract, treat accordingly with an evidence-based formulation and measure the performance of the treatment against those oxidative stress markers. Whether such treatment will also increase pregnancy rates will depend on a variety of other factors that will not necessarily be impacted by antioxidant therapy.  However, if antioxidant therapy can, as the animal models demonstrate, reverse levels of oxidative damage in both the male and female germ lines (29) then at least one component of the overall pregnancy equation will have been successfully addressed. Furthermore, reducing levels of oxidative DNA damage in the male germ line prior to conception is not just about establishing pregnancies per se, but making sure that the mutational load carried by the resultant offspring is kept as low as possible.


In conclusion, the paper by Steiner et al (23) clearly does indicate that the prevailing clinical practice of randomly prescribing antioxidant therapy to the subpopulation of males attending infertility clinics is unlikely to generate any overall benefit. However, this does not mean that carefully formulated antioxidant preparations are without significant therapeutic merit. They just have to be given to patients where there is evidence of oxidative stress as a causative factor in the patients’ infertility profile. This simple requirement has been met in previous small-scale studies and positive outcomes observed (30).  The time has now arrived not for us to abandon this approach to therapy but to replicate such studies at scale, using a randomized, placebo-controlled, double-blinded study design, ensuring that the appropriate patients are selected for treatment and the appropriate assessment criteria are in place to measure the impact of antioxidant intervention.


John Aitken (RJA), Parviz Gharagozloo (PG), Joel Drevet (JD), Jorge Hallak (JH), Alfonso Gutierrez-Adan (AGA), Juan Alvarez, Rafael Ambar, Gihan Bareh, Sheryl Homa, Sergey I. Moskovtsev, Mohammad Hossein Nasr-Esfahani, Cristian O'Flaherty, Suresh Sikka, Steven Somkuti, Paul Turek, Armand Zini.



PG is CEO of a company, CellOxess biotechnology, involved in the design and manufacture of antioxidant formulations for male and female infertility.  RJA, JD, JH and AGA are honorary advisors to this company.


* Correspondence: and



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For such a widespread treatment strategy (i.e. the now practically routine use of antioxidants in subfertile men), one needs to perform a pragmatic RCT! I cannot agree more Dr Coward et al, this is exactly the kind of trial that we needed! Many physicians are unconscious "pill mills" for male fertility supplements, without strong evidence to prescribe them. When a subspeciality has such a large drop-out rate following treatment as ours, one needs to seriously ask whether one of the reasons may not be that we tell patients "take this, you need it" and then nothing changes! The frustration caused by untested strategies may be many times more harmful than the temporary (false) hope these supplements give to the patients.

This is not (nor should it be) the end of testing the potential benefit of antioxidants in men, namely in specific subpopulations. However, this study should be a reminder to us all that we should not promote "one size fits all" and untested treatments.

Replying to Elena Labarta

Thank you very much for exposing the current situation at this time of crisis.

Obviously, the best recommendation is not to transfer embryos while the uncertainty of the effects of COVID-19 on pregnant women and foetuses continues.

I also agree that aggressive ovarian stimulation should be avoided, as this could lead to the risk of ovarian hyperstimulation syndrome and possible hospital admission at a time when hospital beds should be made available for all victims of COVID-19.

A key point is whether the virus can be present in the gametes. As stated in this manuscript: "... in the absence of evidence of transmission of the virus within reproductive cells.... But I am not sure if this has been proven already and, as is well known, "the absence of proof does not proof the absence".

Therefore, until we know this, we could not even consider vitrifying oocytes in our patients, with the consequent risk of allowing their ovarian reserve to diminish over the months.

Clearly, we are in a dramatic situation that will paralyse many things, including assisted reproduction treatments, until we are in a safe situation. Obviously, within 9 months, the birth rate will be reduced worldwide, taking into account the number of children born from assisted reproduction treatments.

We must follow all the recommendations that the health authorities send us, in order to flatten the curve and thus be able to recover as soon as possible from this situation.

Dr Elena Labarta

IVI RMA Valencia, Spain

Excellent comment Elena! Just as ASRM is recommending, I also agree that cases of low ovarian reserve, while time-sensitive, should not be deemed urgent for now to mitigate COVID19 growth. I just hope however that no one starting issuing already "blank statement" on all vitrification cases as some fertility preservations should remain an option even at this time in my view. Specifically, I am concerned that such a strict decision may put in jeopardy the opportunity of fertility preservation in cases of oncofertility. I think a special consent should now be obtained for preservation, but to outright "ban" oocyte vitrification may unnecessarily limit the later options of these oncofertility patients.

Thank you to the ASRM for such a exhaustive overview on this topic and the intent to keep it so regularly updated!

Very interesting strategy to remove some of the biases present in many of the previous studies regarding the time-lapse technology. Any plan on applying this in a randomized fashion (time-lapse versus no time-lapse in couples performing PGT-A)?

Great job!

This is great new information adding more insight on the endometrial scratching dilemma! The investigators challenge us to consider scratching with patients who have suffered 3 or more previous failed implantation attempts based on a subgroup analysis. In the control arm, CPRs seemed relatively stable around 30% regardless of the number or previous transfers. Meanwhile, in the intervention arm, while the overall CPR was around 36%, the CPRs in the subgroup analysis had a stark variation according to whether 1, 2 or 3 previous failed implantation attempts had occurred (38%, 18% and 45%, respectively). How much of this effect is due to the intervention (especially between 1 and 2 previous failures) and how much of it is due to chance?

Very interesting results from the group of Tilia et al, expanding on their previous work from 2016. In one shot, the authors present interesting hypotheses to justify the frequent occurrence of aneuploid and mosaic embryos in ART. Pending further validation, we may soon have a more robust manner to assess oocyte competence.

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