In-vitro maturation versus IVF with GnRH antagonist for women with polycystic ovary syndrome: treatment outcome and rates of ovarian hyperstimulation syndrome

In-vitro maturation (IVM) treatment has gained popularity for decreasing the incidence of ovarian hyperstimulation syndrome (OHSS) by eliminating or minimizing the use of gonadotrophins in women with polycystic ovary syndrome (PCOS). Studies have shown that IVF with GnRH-antagonist protocol is associated with a lower incidence of OHSS. Data comparing the relative success of these two treatments is, however, lacking. Treatment outcome and rates of OHSS were compared in patients with PCOS who underwent assisted conception with either IVM or IVF with GnRH-antagonist protocol between 2006 and 2011. The number of oocytes retrieved was higher in the IVM group, whereas the number of mature oocytes, fertilization rate and number of embryos cleaved were comparable. The implantation rate was higher in the IVF group. The clinical pregnancy rates per embryo transfer were not statistically different (IVF: 45.8% versus IVM: 32.4%). The live-birth rate was higher in the IVF group (IVF: 40.7% versus IVM: 23.5%; P = 0.04). Five women developed moderate or severe OHSS in the IVF group, whereas none did in the IVM group. Both IVM and IVF with GnRH-antagonist protocol seem to be effective treatment regimens in women with PCOS, although IVM is associated with a lower risk of OHSS.     

多囊卵巢综合征妇女体外成熟卵母细胞胚胎慢速冷冻复苏移植结局分析

目的评价未成熟卵母细胞体外成熟（IVM）后形成的卵裂期胚胎经慢速冷冻一解冻后的发育能力。方法将2006年1月至2010年12月北京大学第三医院因多囊卵巢综合征（PCOS）合并不孕症行卵裂期胚胎复苏移植的385例患者分为两组：复苏胚胎来源于体外成熟的卵母细胞组（IVM组,46例）和复苏胚胎来源于常规体内成熟的卵母细胞组（IVF组,339例）。采用慢冻速溶法解冻移植后比较两组患者的临床结局。结果IVM组复苏胚胎243枚,复苏后存活162枚,复苏率为66．67％;IVF组复苏胚胎1605枚,复苏后存活1082枚,复苏率为67．41％,两组比较,差异无统计学意义（P〉0．05）。IVM组患者的临床妊娠率和着床率分别为19．30％（11／57）和10．61％（14／132）,明显低于IvF组临床妊娠率（45．45％,175／385）和着床率（26．14％,240／918;P均〈O．05）。结论体外成熟卵母细胞发育形成的卵裂期胚胎慢速冷冻后临床结局欠佳,可能与冻融前胚胎自身的发育潜力有关。     

A comparison of in vitro maturation and in vitro fertilization for women with polycystic ovaries

OBJECTIVE: To establish the relative success of treatment by unstimulated in vitro maturation (IVM) of oocytes or stimulated in vitro fertilization (IVF) in women with polycystic ovaries undergoing assisted conception treatment. METHODS: The case-control study included 107 IVM and 107 IVF cycles matched for age and cause of infertility. In vitro maturation patients underwent transvaginal recovery of immature oocytes during an unstimulated cycle, in vitro oocyte maturation, and fertilization. Those in the IVF group underwent ovarian stimulation after pituitary suppression. Embryos were transferred in the same cycle in both groups. Main outcome measures included numbers of mature oocytes and embryos produced, and rates of implantation, pregnancy, live birth, and complications. RESULTS: In the IVM group after in vitro culture, 7.8 mature oocytes and 6.1 embryos were obtained per retrieval. With IVF, 12.0 mature oocytes (P <.01) and 9.3 embryos (P <.01) were obtained. The IVM pregnancy and live birth rates per retrieval were 26.2% and 15.9% compared with 38.3% and 26.2% for IVF (nonsignificant). The implantation rate of IVF-derived embryos was higher (17.1% versus 9.5%) than that for IVM (P <.01). There were 12 cases (11.2%) of moderate or severe ovarian hyperstimulation syndrome in IVF patients, compared with none in the IVM group (P <.01). CONCLUSION: Our results suggest that for women with polycystic ovaries who require assisted conception, IVM is a promising alternative to conventional IVF treatment.     

Gonadotrophin regimens and oocyte quality in women with polycystic ovaries

The systemic endocrine environment during the later stages of follicle development has a crucial role in co-ordinating follicular and oocyte maturation before ovulation. Polycystic ovary syndrome (PCOS) is associated with abnormal circulating hormones, abnormal peri-follicular vascularity and significant abnormalities of granulosa cell function. After induction of ovulation, fertilization rates in vivo in women with PCOS are normal, but there is an increased risk of early pregnancy loss, particularly in obese patients. After in-vitro maturation of oocytes or following ovulation induction for IVF, oocyte and embryo quality in vitro are not obviously impaired in PCOS. In some reports however, specific endocrine abnormalities, such as hyperinsulinaemia/insulin resistance, have been noted to be associated with reduced fertilization rates and abnormal early embryonic development.     

PCOS患者未成熟卵体外成熟培养后妊娠结局分析

目的:探讨PCOS患者未成熟卵母细胞体外成熟(in vitro maturation,IVM)治疗的有效性和安全性。方法:分析比较PCOS合并不孕症自愿要求行IVM或IVF治疗的患者临床结局。结果:IVF组的平均优质胚胎数明显高于IVM组(P<0.05),两者的临床妊娠率(39.22%vs 40.32%)和着床率(24.37%vs 23.89%)无差异(P>0.05)。IVM组的妊娠丢失率为38.0%,高于IVF患者(21.1%,P<0.05),出生婴儿(单胎)的平均体质量组间无统计学差异(P>0.05)。结论:对于PCOS患者进行IVM治疗可以获得与IVF周期相类似的临床妊娠率和着床率;但是IVM治疗后流产率明显增加。     

IVF versus ICSI for the fertilization of in-vitro matured human oocytes

Traditional dogma suggests that intracytoplasmic sperm injection (ICSI) should be performed to ensure successful oocyte fertilization in an in-vitro maturation (IVM) cycle. This study postulated that there would be no difference in the fertilization rate when ICSI was compared with IVF. This hypothesis was tested in a randomized trial of IVF versus ICSI in IVM. A total of 150 immature oocytes were collected in eight cycles of IVM for patients diagnosed with polycystic ovarian syndrome (PCOS). Patients were primed with minimal FSH before transvaginal oocyte aspiration. Sibling oocytes were inseminated by 50% IVF and 50% ICSI. There was no significant difference in fertilization, useable or total blastocyst development between the two insemination technique groups. Clinical pregnancy results for combined fresh and cryopreserved transfers were identical between the two insemination techniques with a total of two fresh and five cryopreserved IVF-inseminated embryos resulting in three clinical pregnancies (42.9%) and five fresh and two cryopreserved ICSI-derived embryos resulting in three clinical pregnancies (42.9%). This research has shown IVF to be a legitimate fertilization technique for IVM oocytes in PCOS patients and provides a greater awareness of the use of a fertilization method previously not utilized with IVM.In-vitro maturation (IVM) is an alternative treatment method to traditional IVF. Due to the minimal use of stimulating hormones in this treatment, IVM has a lower risk of ovarian hyperstimulation syndrome, it can be used for fertility preservation in cancer patients and it is more cost conservative. Early research into the effects of IVM showed a hardening effect on the membrane surrounding the egg (the zona pellucida). It was initially believed that, to overcome this hardening in order to allow the egg to be fertilized, spermatozoa would need to be injected into the egg using intracytoplasmic sperm injection. Due to recent advances in hormonal stimulation protocols (FSH priming) and culture conditions, we postulated that, for patients suffering from polycystic ovarian syndrome (PCOS), fertilization, embryo development and clinical pregnancy would not be superior in the injected oocytes compared with those inseminated by IVF. We found that by using the two insemination techniques on sibling oocytes from eight PCOS patients, there was no significant difference in fertilization, useable or total blastocyst development (day 5 or 6 embryos) and that clinical pregnancy results were identical. This research provides a greater awareness of a fertilization technique which is not normally utilized for IVM treatment, providing a less invasive, more cost-effective approach for the patient.     

多囊卵巢综合征患者卵丘形态与未成熟卵母细胞发育潜能关系

目的 研究多囊卵巢综合征患者无刺激周期取出的不同形态未成熟卵母细胞的发育潜能。方法 43例PCOS不孕患者进行了47个未成熟卵母细胞体外成熟培养（IVM）周期。所有患者均未经促卵泡素刺激,予以HCG36h后取卵。根据取出的卵-冠-丘复合物形态将其分为3组：卵丘紧密组、卵丘松散组、无卵丘组。比较3组的体外成熟率、受精率和优质胚胎率。结果 47个IVM周期共收集未成熟卵母细胞874枚,体外成熟率61.19%,受精率71.07%,着床率13.13%。卵丘松散组的体外成熟率明显高于卵丘紧密组（72.26%vs49.54%,P〈0.05）,受精率、优质胚胎率三组间无差异。结论 PCOS患者无刺激周期取出的未成熟卵母细胞中,卵丘松散、扩张的卵母细胞具有更好的体外成熟潜力。     

Oocyte and embryo quality in polycystic ovary syndrome

OBJECTIVE: To compare oocyte and embryo quality in women with Polycystic Ovary Syndrome (PCOS) and in women with normal ovulation. PATIENTS AND METHODS: Forty women with PCOS underwent a total of 67 In Vitro Fertilization (IVF) or Intracytoplasmic Sperm Injection (ICSI) cycles. The control group consisted of women, of the same age, who underwent IVF (for tubal infertility) or ICSI (for male factor infertility) in the same period. RESULTS: The average number of oocytes recovered was higher in the PCOS group (12,1) than in the control group (9.6) as was the rate of immature oocytes (13.8% vs 5.8%; respectively). The fertilization rate was lower in PCOS patients (52% vs 61% in the controls). The cleavage rates, embryo morphology and pregnancy rates were similar in both groups. DISCUSSION AND CONCLUSIONS: Although more oocytes were recovered from PCOS patients, the number of good quality embryos, suitable for transfer or freezing was similar in the two groups as less of the oocytes were mature and the fertilization rate was lower in the PCOS group. IVF or ICSI (according to the indication) are therefore efficient in PCOS patients.     

In vitro maturation for patients with polycystic ovary syndrome

In vitro fertilization (IVF) with ovarian stimulation is an effective treatment for couples needing treatment with assisted reproductive technologies (ART) where polycystic ovary syndrome (PCOS) is coexisting. However, it is also associated with an increased risk of ovarian hyperstimulation syndrome. In vitro maturation (IVM) avoids the risks and side effects of ovarian stimulation by retrieving immature oocytes from unstimulated ovaries. These immature oocytes are then cultured, matured, and fertilized in vitro. Embryos are then selected for transfer in the same manner as conventional IVF. Although there has been significant progress in terms of improving clinical pregnancy and live-birth rates after IVM, there remains much to learn in terms of what controls maturation, fertilization, and implantation rates. This review is intended as an update on the most recent advances and directions of ongoing research in IVM in patients with PCOS.     

无刺激周期未成熟卵母细胞体外培养用于多囊卵巢综合征不孕患者治疗的临床观察

目的探讨无刺激周期未成熟卵母细胞体外培养在治疗多囊卵巢综合征(PCOS)不孕患者的应用价值。方法对70例PCOS患者,在人工周期或自然周期第10～12天行阴道B超监测,如双侧卵巢中无直径>8mm的卵泡,即肌内注射人绒毛膜促性腺激素10000IU,36h后经阴道穿刺取卵,将取出的未成熟卵母细胞进行体外成熟及体外受精胚胎移植。结果共进行体外成熟周期94个,移植周期75个。共获得卵母细胞1283个,获得成熟838个(65.3%,838/1283),其中受精553个(66.0%,553/838),获得胚胎402个(48.0%,402/838),获得优质胚胎199个(23.7%,199/838)。生发泡期卵母细胞的成熟率、受精率、获得胚胎率及优质胚胎率,分别为67.7%、66.4%、47.6%及24.1%;第1次减数分裂中期的卵母细胞,分别为69.7%、71.7%、52.2%及26.1%,生发泡期与第1次减数分裂中期比较,差异均无统计学意义(P>0.05)。无法评价的卵母细胞的成熟率、受精率、获得胚胎率及优质胚胎率,分别为44.8%、53.8%、46.2%及16.9%,与生发泡期及第1次减数分裂中期比较,差异均有统计学意义(P<0.05)。75个移植周期中,18例获得临床妊娠,妊娠率为24%(18/75)。结论无刺激周期未成熟卵母细胞体外成熟及体外受精胚胎移植可用于PCOS不孕患者的治疗,并能取得一定的妊娠成功率。     

Retrospective comparison of two media for invitro maturation of oocytes

In-vitro maturation of oocytes (IVM) is a new IVF technology developed in order to avoid iatrogenic complications of standard IVF treatments. This technique is particularly useful in patients suffering from polycystic ovary syndrome (PCOS) who are concerned with the risk of ovarian hyperstimulation syndrome. This technique is nowadays routinely practised in many international centres. However, the efficiency of this technique needs to be improved for a better support of maturation conditions to maximize oocyte developmental competence. In order to improve IVM results, the efficiency of two IVM media was retrospectively compared. Ninety-three PCOS candidates undergoing their first IVM cycle were included in this study, and IVM was conducted with TCM-199 or IVM-Medicult medium. This is the first study comparing two maturation media. Both media resulted in the same results concerning total oocyte maturation, fertilization, early embryo development and pregnancy rates.     

In-vitro maturation of oocytes from unstimulated polycystic ovaries

In-vitro fertilization (IVF), an established treatment for infertility, may result in pregnancy and live-birth rates higher than following natural conception in fertile couples. However, IVF is associated with two major complications, namely, multiple pregnancy and ovarian hyperstimulation syndrome. The latter is a consequence of the ovarian stimulation required for IVF. Women with polycystic ovaries (PCO) are at increased risk of developing this complication. Ovarian stimulation is not required for in-vitro maturation (IVM) of immature oocytes. This approach is therefore both cheaper and safer than IVF, particularly for women with PCO. It has been found that the IVM pregnancy rate is correlated with the number of antral follicles present, the peak ovarian stromal blood flow velocity at the baseline ultrasound scan, the number of immature oocytes collected, absence of a dominant follicle at the time of immature oocyte retrieval, and endometrial thickness at embryo transfer. The indications for IVM at present would include women requiring IVF who have PCO, those with primarily poor quality embryos in repeated previous IVF cycles for no apparent reason, poor responders to high dose gonadotrophin stimulation for IVF, and finally, women with PCO who are considering egg donation.     

Effect of myo-inositol and melatonin versus myo-inositol,in a randomized controlled trial,for improving in vitro fertilization of patients with polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) induces anovulation in women of reproductive age, and is one of the pathological factors involved in the failure of in vitro fertilization (IVF). Indeed, PCOS women are characterized by poor quality oocytes. Therefore, a treatment for enhancing oocyte quality becomes crucial for these patients. Myo-Inositol and melatonin proved to be efficient predictors for positive IVF outcomes, correlating with high oocyte quality. We tested the synergistic effect of myo-inositol and melatonin in IVF protocols with PCOS patients in a randomized, controlled, double-blind trial. Five-hundred twenty-six PCOS women were divided into three groups: Controls (only folic acid: 400?mcg), Group A (Inofolic® plus, a daily dose of myo-inositol: 4000?mg, folic acid: 400?mcg, and melatonin: 3?mg), and Group B (Inofolic®, a daily dose of myo-inositol: 4000?mg, and folic acid: 400?mcg). The main outcome measures were oocyte and embryo quality, clinical pregnancy and implantation rates. The treatment lasted from the first day of the cycle until 14 days after embryo transfer. Myo-inositol and melatonin have shown to enhance, synergistically, oocyte and embryo quality. In consideration of the beneficial effect observed in our trial and on the bases of previous studies, we decided to integrate routinely MI and M supplementation in the IVF protocols. The same treatment should be taken carefully in consideration in all procedures of this kind.     

未经促排卵的未成熟卵母细胞行体外成熟治疗不孕症的临床研究

目的探讨未经任何药物刺激的未成熟卵母细胞行体外成熟（IVM）治疗不孕症的临床价值。方法40例不孕患者接受54个IVM周期,其中多囊卵巢综合征（PCOS）不孕患者26例,经其他辅助生育技术失败14例。在未采用任何药物刺激的前提下,于月经周期的第9—12天,在超声引导下经阴道对两侧卵巢内直径≤10mm的卵泡进行穿刺取卵。对取出卵母细胞于体外培养24～48h,待第一极体出现后,进行卵母细胞质内单精于注射（ICSI）,18h后观察受精情况,继续培养24—48h,直至胚胎移植,移植前行激光辅助胚胎孵化。结果54个IVM周期中,有7个周期取消,取消率为13％;共移植周期47个,共获得未成熟卵母细胞857个,平均每周期18．2个。体外培养48h后,卵母细胞成熟率为73．7％（632／857）,正常受精率为75．3％（476／632）,卵裂率为91．2％（434／476）。移植日子宫内膜厚度平均为8．9mm,平均移植胚胎4．3个（2—6个）;1例生化妊娠,19例临床妊娠,每取卵周期的临床妊娠率为35％（19／54）,每移植周期的临床妊娠率为40％（19／47）。26例PCOS不孕患者共移植周期34个,1例生化妊娠,15例临床妊娠,每移植周期的临床妊娠率为44％（15／34）。结论未经促排卵药物刺激的卵母细胞行IVM用于治疗各种原因的不孕症,尤其是PCOS不孕患者,是一种有效的治疗方法。     

三种助孕技术治疗多囊卵巢综合征不孕的疗效比较

目的：观察３种助孕技术：ＩＶＦ ＥＴ、ＧＩＦＴ和控制性超促排卵（ＣＯＨ）后自行同房对多囊卵巢综合征（ＰＣＯＳ）不孕患者的疗效。方法：应用３种方法治疗,观察各组的临床妊娠率和发生卵巢过度刺激综合征（ＯＨＳＳ）的情况。结果：ＩＶＦ ＥＴ和ＧＩＦＴ与ＣＯＨ相比能得到更高的临床妊娠率,而前二者发生ＯＨＳＳ的危险性明显低于后者。结论：为避免ＣＯＨ后发生ＯＨＳＳ,建议对因ＰＣＯＳ不孕的患者采取体外助孕技术治疗。应用何种技术要根据患者的具体情况而定。如果有至少１ 条输卵管完全正常,可先试行ＧＩＦＴ。此外,须将多余的卵子进行体外授精试验,观察其受精及卵裂情况,从而对今后的治疗提出指导性建议,并要将得到的胚胎进行冷冻保存,以备今后使用。     

Supplemented tissue culture medium 199 is a better medium for in vitro maturation of oocytes from women with polycystic ovary syndrome women than human tubal fluid

OBJECTIVE: To compare oocyte maturation, fertilization and cleavage rates, and embryonic developmental quality after culture of human immature oocytes from polycystic ovary syndrome (PCOS) patients in human tubal fluid (HTF) or tissue culture medium (TCM) 199. DESIGN: Prospective, randomized, controlled trial. SETTING: University hospital. PATIENT(S): Thirteen women undergoing 23 in vitro maturation cycles, from whom 119 oocytes were retrieved. INTERVENTION(S): Cumulus-enclosed germinal vesicle-stage oocytes matured in TCM-199-supplemented or HTF-supplemented media. MAIN OUTCOME MEASURE(S): Oocyte maturation and fertilization rates, embryonic developmental quality. RESULT(S): Significant differences were observed between TCM 199 and HTF regarding maturation rate (82% vs. 56.9%), fertilization rate (70% vs. 39.4%), and embryo quality (81.3% vs. 41.7%). CONCLUSION(S): Human tubal fluid medium, although widely used for embryo fertilization and maintenance in IVF techniques, is not an appropriate medium for the maturation of oocytes obtained from PCOS patients in nonstimulated cycles.     

多囊卵巢患者行未成熟卵母细胞体外成熟、受精和胚胎发育观察

目的:探索在不用或小剂量使用促性腺激素条件下对多囊卵巢患者的未成熟卵母细胞体外培养至成熟、受精、卵裂和妊娠的可行性。方法:阴道B超引导下穿刺取卵后将卵子分别培养于3种不同培养基:基本培养基(f-HTF+75 mIU/mL rFSH+500 mIU/mL rhCG)+10%SPS(SPS组), 基本培养基+20% hFF(FF组)和基本培养基+20% hFF+2 ng/mL rEGF(FF+EGF组),共培养25-48 h,然后行体外受精和胚胎培养。结果:体外培养卵丘-卵母细胞复合体102个,成熟率65.69%,受精率83.58%,2PN率71.43%,卵裂率51.72%,优质胚胎率40.00%。FF组较SPS组有更高的成熟、受精、卵裂和优质胚胎率,再添加EGF后卵子的成熟、受精和优质胚胎率增加。刺激组和未刺激组在卵子成熟、受精、卵裂和优质胚胎率方面均无显著差异。PCO患者卵子的成熟、受精、卵裂和优质胚胎率均高于PCOS患者,ICSI组优质胚胎率增加,但均无统计学差异。随培养时间延长,卵子的成熟、受精、卵裂和优质胚胎率均升高,其中正常受精率和卵裂率有显著差异(P<0.05)。结论:PCO和PCOS患者行IVM可行,二者无明显差异。培养液中添加激素、FF、EGF以及延长培养时间至48 h,可促进卵子成熟。但有关临床用药、培养条件仍有待改善,进一步提高卵子和胚胎质量以获得妊娠。     

体外成熟卵母细胞体外受精方式的探讨

目的:探讨经体外成熟卵母细胞是否可采用常规IVF方式授精。方法:自愿捐献的常规废弃的未成熟卵母细胞经体外成熟后的卵母细胞206个,随机分为3组:A组(n=69),授精时尽可能保存卵丘细胞并行常规IVF授精;B组(n=68),授精前将卵丘细胞完全拆除后行常规IVF授精;C组(n=69),将卵丘细胞完全拆除后行ICSI授精。常规IVF授精的精/卵个数比约为50 000∶1。比较3组卵子的受精率、卵裂率和优质胚胎率。结果:A组与C组在受精率(82.61%vs 85.51%)、卵裂率(94.74%vs 94.92%)、优质胚胎率(42.59%vs 46.43%)3个方面均无统计学差异(P>0.05),A组、C组的受精率、卵裂率均显著高于B组(14.71%,50.00%)(P<0.01),B组没有优质胚胎出现。结论:体外成熟后的卵母细胞在卵丘细胞较完整时可进行常规IVF方式授精。     

超排卵周期未成熟卵体外培养的研究

目的:研究来源于超排卵周期中的未成熟卵在拆除卵丘细胞后进行体外成熟培养(IVM)的成熟、受精及胚胎发育能力,探讨IVM技术的临床应用。方法:选取46名体外受精/卵胞浆内单精子显微注射-胚胎移植(IVF/ICSI-ET)患者为研究对象,比较MI和GV期不成熟卵的体外成熟情况,并比较体内成熟卵和体外成熟卵进行ICSI后的正常受精、异常受精、卵裂和优质胚胎形成情况。结果:体外培养中69.8%的MI期卵和77.2%的GV期卵均在24小时内达到成熟,其24小时和48小时的成熟率、总成熟率均无明显差异(P>0.05)。体外成熟卵与体内成熟卵相比较,正常受精率、异常受精率和卵裂率均无明显差异(P>0.05),优质胚胎形成率较低,差异有显著性(P<0.05)。结论:常规超排卵周期中的未成熟卵在拆除卵丘细胞后能够继续体外发育成熟,具有与体内成熟卵相似的ICSI受精、卵裂能力。虽然优质胚胎的形成率低于体内成熟卵,但增加了可移植胚胎和冷冻胚胎数量,提高了助孕成功率。     

Vitrification of human immature oocytes before and after in vitro maturation: a review

The use of immature oocytes subjected to in vitro maturation (IVM) opens interesting perspectives for fertility preservation where ovarian reserves are damaged by pathologies or therapies, as in PCO/PCOS and cancer patients. Human oocyte cryopreservation may offer some advantages compared to embryo freezing, such as fertility preservation in women at risk of losing fertility due to oncological treatment or chronic disease, egg donation and postponing childbirth. It also eliminates religious and/or other ethical, legal, and moral concerns of embryo freezing. In addition, a successful oocyte cryopreservation program could eliminate the need for donor and recipient menstrual cycle synchronization. Recent advances in vitrification technology have markedly improved the oocyte survival rate after warming, with fertilization and implantation rates comparable with those of fresh oocytes. Healthy live births can be achieved from the combination of IVM and vitrification, even if vitrification of in vivo matured oocytes is still more effective. Recently, attention is given to highlight whether vitrification procedures are more successful when performed before or after IVM, on immature GV-stage oocytes, or on in vitro matured MII-stage oocytes. In this review, we emphasize that, even if there are no differences in survival rates between oocytes vitrified prior to or post-IVM, reduced maturation rates of immature oocytes vitrified prior to IVM can be, at least in part, explained by underlying ultrastructural and biomolecular alterations.