Introduction

Polycystic ovarian syndrome (PCOS) occurs in 5% to 10% of all women of reproductive age and 50% of women who present with sub-fertility [1]. Clear diagnostic criteria for this condition were identified at the consensus meeting of the European Society of Human Reproduction and Embryology and the American Society for Reproductive Medicine [2]. Sub-fertile women with PCOS will usually benefit from conventional treatments, such as lifestyle changes, laparoscopic ovarian drilling or ovulation induction [3–5], but some will ultimately need assisted reproductive techniques, either if they will need or if they wish, such as controlled ovarian hyperstimulation and IVF. In these cases, controlled ovarian hyperstimulation is closely related to high drug costs, need for daily injections and frequent monitoring, whereas it sometimes results in an increased rate of cycle cancellations and potential life threatening complications due to ovarian hyperstimulation syndrome and in the retrieval of immature oocytes, leading to poor fertilization and lower cleavage, pregnancy, and live birth rates compared to the conventional IVF cycles [6], although this has not been confirmed by other studies [7,8]. In addition, ovulation induction is associated with a high risk of multiple pregnancies due to multiple follicular development, so that it has to be individualized and closely monitored [9].

In order to overcome these complications, in vitro maturation (IVM) has been suggested. It involves the in vitro culture of immature oocytes, from the germinal vesicle or the germinal vesicle breakdown stage, in special laboratory conditions until the metaphase II stage, along with the accompanying cytoplasmic maturation, when the oocyte is considered to be completely mature and ready to undergo fertilization [10]. This can be a potentially useful intervention for women with PCOS-related sub-fertility since these oocytes can retain their maturational and developmental competence after their preterm retrieval from the ovaries [11]. IVM has been also successfully used in a wide range of sub-fertile women, such as poor or high responders undergoing IVF who were at risk for ovarian hyperstimulation syndrome, in women who sought an alternative to conventional IVF in terms of drugs or others for fertility preservation or leukemia/cancer, in those with high antral follicle count scores or in those who wish to avoid gonadotrophin therapy, or in those suffering from ovarian resistance to FSH [12–14].

It remains unclear though, whether PCOS itself contributes to a compromised endometrial receptivity and oocyte quality and whether these lead to reduced fertilization and implantation rates observed after conventional assisted reproduction techniques. Thus, these women who are at risk of developing ovarian hyperstimulation syndrome, following a conventional controlled ovarian hyperstimulation regimen, might benefit from earlier retrieval of oocytes followed by IVM; of note, in such cases, the need for drugs is minimal and often negated. The rationale lies to the in vitro replacement of the oocytes maturation instead of within the ovary. In the context of PCOS, IVM is a mild-approach assisted reproduction technique with no reported cases of ovarian hyperstimulation syndrome. Successful fertilization, embryo development, and term pregnancy resulting from IVM oocytes have been reported [11–13,15–20], obtaining a pregnancy rate up to 35–40% [20], with the first report to be published in the mid 60s [21], and the first pregnancy in an anovulatory PCOS woman in 1994 [11].

The concern expressed regarding the safety of the method with respect to the health of the children, through the in vitro culture conditions [22,23], has been doubted by others who have reported normal obstetric and neonatal outcomes in PCOS [13,24]. Further worries have been reported on low pregnancy and live birth rates, as compared to conventional assisted reproduction techniques [16,25]. There are reports to suggest that IVM should be kept aside and performed only in certain cases when no other option is available, such as in sub-fertile cancer patients, as there are other / newer options for controlled ovarian hyperstimulation in women at high risk for ovarian hyperstimulation syndrome [26]. In a recent update of a Cochrane review, the comparison of IVM to conventional IVF treatment was assessed [27]; nevertheless, the potential differential efficacy of IVM in PCOS versus non-PCOS subjects has not been yet addressed, in the context of a meta-analysis.

The rationale for the current systematic review lies on the fact that sub-fertility with PCOS needing IVF compared with sub-fertility from all other causes (including PCO–polycystic ovaries) could yield different results regarding various outcomes, such as cycle cancellation, pregnancy and live birth rates, when treated with IVM. The triad PCOS—PCO—controls may represent a challenging notion from a methodological point of view. Although complex techniques such as network meta-analysis would seem tempting in this context, close examination of the published literature reveals that the existing corpus of evidence comes exclusively from non-randomized studies. Hence, the background assumptions underlying network meta-analysis, encompassing the existence of randomized controlled trials [28] are not fulfilled; consequently, we approached the aforementioned pattern mainly examining the comparison between PCOS vs. non-PCOS subjects, with the latter group consisting of PCO and/or control subjects. Secondly, in an attempt to evaluate the impact of the reference group, we subdivided the PCOS vs. non-PCOS contrast into separate examination of the PCOS vs. controls and PCOS vs. PCO comparisons. We also evaluated the impact of stimulation and/or priming with gonadotrophins.

Methods of Review

Results

Selection and description of included studies

A total of 268 PCOS patients (328 cycles), 100 PCO patients (110 cycles) and 440 controls (480 cycles) were included in the meta-analysis. Responses of authors contacted for the requested data was satisfactory in more than half of cases.

The initial literature search yielded 1255 potentially relevant studies (Fig 1). All titles were carefully checked to exclude irrelevant publications, resulting in 219 potentially eligible studies. The abstracts of these studies were re-examined and eventually 102 manuscripts that provided data to answer the research question were identified. The full text of these studies was examined thoroughly, resulting in the exclusion of 91 (Table A in S2 File). Eventually, 11 studies were considered eligible for inclusion in the meta-analysis [11–13,18,23,34–39]. Characteristics of the studies included are presented in Table 1.

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Fig 1. PRISMA Flow Diagram of the studies.

https://doi.org/10.1371/journal.pone.0134696.g001

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Table 1. Characteristics of included studies.

https://doi.org/10.1371/journal.pone.0134696.t001

Definition of PCOS according to the European Society of Human Reproduction and Embryology and the American Society for Reproductive Medicine criteria was given in 7 out of 11 studies. In the remaining four reports [11,12,34,38], conducted before 2003, these criteria had not been established yet; nevertheless, the definitions adopted therein were largely compatible with the rationale of European Society of Human Reproduction and Embryology and the American Society for Reproductive Medicine criteria (Table 2). The two largest studies published so far investigating the research question were by Child et al and Junk et al conducted in 2001 and 2012, respectively [12,36], involving 99 PCOS patients and 108 controls in total. The comparison group consisted of PCO women in five studies [11–13,34,36] and in eight of women/couples suffering from other causes of sub-fertility [12,13,18,23,34,37–39].

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Table 2. Description of cycle and outcome parameters.

https://doi.org/10.1371/journal.pone.0134696.t002

HCG was used to trigger final oocyte maturation in five studies [12,13,23,37,39], mild stimulation with FSH was used in five studies [35–39], while in three no hormonal priming was used [11,18,34] (Table 2). No studies reported on ovarian hyperstimulation syndrome and preterm birth, whereas one study reported on congenital abnormalities [23].

Synthesis of studies

Table 3 presents the results of the meta-analysis, by outcome and comparison group. Live birth rates did not differ between PCOS and non-PCOS subjects, at the cycles-based analysis (Figures A-C in S1 File); however, at the women-based analyses (Fig 2 and Figures B, D in S1 File), a borderline trend towards higher birth rates among PCOS patients emerged (pooled OR = 1.74, 95%CI: 0.99–3.04, p = 0.053, Fig 2), mainly reflected at the subgroup analysis vs. controls (pooled OR = 3.72, 95%, CI: 0.95–14.49, p = 0.059, Figure Bb in S1 File).

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Fig 2. (a). Comparison PCOS vs. non-PCOS regarding live birth rates (women-based analysis), stratified by stimulation with FSH. (b) Comparison PCOS vs. non-PCOS regarding live birth rates (women-based analysis), stratified by priming with hCG.

https://doi.org/10.1371/journal.pone.0134696.g002

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Table 3. Results of the meta-analyses addressing the three comparisons (PCOS vs. controls; PCO vs. controls; PCOS vs. PCO) in the examined outcomes (Bold cells denote statistically significant associations).

https://doi.org/10.1371/journal.pone.0134696.t003

Regarding clinical pregnancy (Fig 3 and Figures E-I in S1 File), higher rates were noted between PCOS and non-PCOS subjects both at the cycles-based analysis (pooled OR = 2.23, 95%CI: 1.45–3.43, Figure E in S1 File) and the women-based approach (pooled OR = 2.37, 95%CI: 1.53–3.68, Fig 3). Once again, these associations were reproduced upon the analysis versus controls (pooled OR = 3.09, 95%CI: 1.46–6.53, Figure F in S1 File) and (pooled OR = 3.29, 95%CI: 1.42–7.62, Figure H in S1 File). Accordingly, implantation rates were higher in PCOS versus non-PCOS subjects (pooled OR = 1.73, 95%CI: 1.06–2.81, Figure J in S1 File); nevertheless, statistical significance was not reached at the subgroup analyses despite the sizeable effect estimates, possibly due to the smaller number of study arms and included cases (Figure K in S1 File).

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Fig 3. (a). Comparison PCOS vs. non-PCOS regarding clinical pregnancy rates (women-based analysis), stratified by stimulation with FSH. (b) Comparison PCOS vs. non-PCOS regarding clinical pregnancy rates (women-based analysis), stratified by priming with hCG.

https://doi.org/10.1371/journal.pone.0134696.g003

Cancellation rates (Figures K-M in S1 File) were lower among PCOS patients (pooled OR = 0.18, 95%CI: 0.06–0.47, Figure L in S1 File), with this pattern replicated in both subgroup analyses (pooled OR = 0.15, 95%CI: 0.05–0.44 vs. controls, Figure M in S1 File; pooled OR = 0.25, 95%CI: 0.07–0.92 vs. PCO subjects, Figure N in S1 File).

Maturation rates (Figures O-Q in S1 File) did not differ between the compared groups, with the exception of lower rates among PCOS patients vs. controls (pooled OR = 0.74, 95%CI: 0.59–0.93, Figure P in S1 File).

Regarding fertilization rates (Figures R-T in S1 File), a borderline trend towards lower rates among PCOS patients was observed (pooled OR = 0.78, 95%CI: 0.60–1.03, p = 0.080, vs. non-PCOS, Figure R in S1 File; pooled OR = 0.76, 95%CI: 0.55–1.04, p = 0.089, vs. controls, Figure S in S1 File). Miscarriage rates did not differ between the examined groups (Figures U,V in S1 File). Table B in S2 File presents the secondary analysis within the non-PCOS women group (PCO vs. control women); no statistically significant differences were noted therein (Figures W-AC in S1 File), but only two studies provided the relevant data.

Conclusions

The performed meta-analysis provided evidence demonstrating that IVM seems to be a preferable approach in treating women with PCOS during an IVF cycle as compared to those without the syndrome. Based on 11 trials with 268 PCOS, 100 PCO patients and 440 women with other causes of sub-fertility, we conclude that IVM appears to be a more efficient treatment option in terms of clinical pregnancy, implantation and cycle cancellation rates in women with PCOS when compared to the non-PCOS group; importantly, we also observed a borderline but meaningful trend in live birth rates in the PCOS group, favoring IVM.

Towards investigation of our research question, we compared IVM outcome on specific parameters, for populations with and without PCOS, including controls (normal ovarian function) and women with PCO. Women with PCOS comprise an ideal target group for IVM, since they present with greater number of antral follicles per ovary, as compared with non-PCOS and importantly, these are more likely to experience ovarian hyperstimulation syndrome. Unexpectedly, our initial search revealed that the majority of studies investigating IVM in sub-fertile PCOS women were not comparative [27]. A number of these studies pointed to similar outcomes for women with and without PCOS undergoing IVM, but without performing formal comparisons [16,22].

Our meta-analysis suggests a relative preponderance of the PCOS group regarding the primary outcome in women-based analysis, reported in four [12,13,35,36] out of the 11 included studies. This finding opposes to the reported–and possibly expected- results so far [40]. Equally important is the significant difference observed in the secondary outcomes of this study (pregnancy, implantation and cycle cancellation rates), reported in seven [11–13,18,35,36,38], three [12,13,35] and six [11–13,18,35,36] included studies, respectively. Moreover, maturation rates, between PCOS and non-PCOS groups, as reported in eight studies [11–13,34–37,39], were similar, apart from the comparison of PCOS with the control population, where proved inferior, a finding that was rather expected for PCOS patients. Adversely, there was a trend towards lower fertilization rates (8/11 studies) [11–13,34–38], in PCOS patients, although this was not observed in miscarriage rates (4/11 studies) [12,13,23,36].

In addition, no differences were observed between women with PCO and women with normal ovarian function, demonstrating that both groups share the same results among the non-PCOS populations in terms of IVM outcome. Results have been previously reported, emphasizing the need for further investigation of the effect of gonadotrophin priming in IVM, both in a clinical and an embryology laboratory setting [40]; of note, the number of included study arms in the subgroup analyses pertaining to either gonadotrophin stimulation or priming was limited in our approach, not allowing reaching safe conclusions. Similarly, in the subgroup analysis IVF versus ICSI, the better performance of PCOS vs. non-PCOS tended to be more sizable in studies adopting IVF, probably denoting an “interventional” negative effect of ICSI on the immature oocyte; however, the small number of study arms does not allow firm conclusions to be drawn.

During IVF, women with PCOS have theoretically an increased risk of cycle cancellation and developing ovarian hyperstimulation syndrome, while usually a poorer outcome is expected. Despite this, previous data has presented similar pregnancy and live birth rates per cycle, although cancellation rates tend to be higher, as opposed to the lowered fertilization rates [7]. Elevated E₂, LH and androgen levels appear to play a key role, as these possibly exert a detrimental effect in oocyte maturation and embryonic development [27]. During IVM, ovarian stimulation is minimal or even absent and this partially explains the findings of the current review.

The remainder outcome parameters (ovarian hyperstimulation syndrome and preterm birth) initially included in our search strategy, were not reported in any of the comparative studies included in our review. The presence of congenital anomalies, following birth, was only reported in one study [23] and therefore no definite conclusions could be drawn.

No significant statistical heterogeneity was observed in the majority of the performed analyses. Accordingly, the PCOS group was clearly described even in the four studies conducted before the establishment of the European Society of Human Reproduction and Embryology and the American Society for Reproductive Medicine criteria, whereas the oocyte retrieval and maturation protocols were similar for all included studies.

The present meta-analysis, despite its originality, bears certain limitations essentially reflecting those of the published literature. First, no RCTs were identified, as the comparison (i.e. PCOS vs. non-PCOS) cannot be randomly assigned; moreover, the sample size of the included studies was rather small, possibly hampering the statistical power in some analyses. For instance, the difference between PCOS and non-PCOS subjects regarding live birth rates was of borderline significance (p = 0.053, women-based analysis); according to our power calculation (data not shown), a sample of 175:350 women would be needed for the optimal power of 90%, whereas our meta-analysis included 161:353 women. This implies that the addition of a slightly larger number of cases may well result in the emergence of formal significance concerning live birth rates. Moreover, the fact that less than 10 study arms were included in the comparisons did not allow the reliable performance of meta-regression analysis, as stated in the Cochrane Handbook for Systematic Reviews of Interventions [33]; therefore, the potential modifying effects mediated by meaningful factors, such as age, could not be assessed. In any case, however, the modifying effect of age seemed rather minimal, as the mean age of included subjects in the eligible studies ranged minimally, namely between 28.3 [35] and 34.3 years [39]. Furthermore, the eligible studies corresponded to 268 PCOS patients, 100 PCO subjects and 440 controls, namely to groups with unequal numbers, whereas the results would ideally have been based on almost equally sized treatment groups. In addition, the variability in the definition of PCOS might be considered as a potential source of heterogeneity, as the European Society of Human Reproduction and Embryology and the American Society for Reproductive Medicine criteria were adopted in seven out of 11 studies; nevertheless, the criteria in the remaining four reports [11,12,34,38] are largely compatible with this rationale. Finally, given the variable clinical settings and countries in which the eligible studies were performed, it would seem desirable to anticipate a future, large clinical trial on comparable PCOS, PCO and control subjects with strict follow-up and documentation of outcomes, aiming to further validate the clinical relevance of previously published results which this meta-analysis succinctly summarized.

For the complete evaluation of the effectiveness of IVM in PCOS, further parameters should be taken into consideration. Importantly, the safety of IVM should be efficiently evaluated by including long-term findings (>10 years follow-up) to examine potential developmental and undiscovered congenital anomalies of the offspring, while the cost of the modality for both individuals and national health system/insurance bodies should be evaluated. Finally, properly conducted prospective studies with larger samples are required in order to confirm the findings of the current review.

Supporting Information