The Biology of IVM

Central to the understanding of the control of oocyte maturation is the understanding of the mechanisms that control meiotic arrest, and those that trigger meiotic resumption. The pre-ovulatory surge of Luteinizing Hormone (LH) or hCG appears to initiate the resumption of meiosis [5] via the blockage of the gap junctions. Without the meiosis-arresting factor, the oocyte resumes meiosis and progresses to metaphase II (MII), the developmental stage at which the oocyte is usually ovulated.

In IVM, immature germinal vesicle oocytes (prophase 1) are retrieved transvaginally under ultrasound guidance from antral follicles before the emergence of a dominant follicle in unstimulated or minimally stimulated ovaries. These oocytes are matured in-vitro under controlled conditions for 24-48 hours. Oocyte maturation consists of both nuclear and cytoplasmic maturation. Nuclear maturation involves resumption of the first meiotic division at the germinal vesicle stage to produce a MII gamete. At this stage, the meiosis is again arrested, awaiting the signal to resume in concert with sperm penetration. In cytoplasmic maturation, the oocyte cytoplasm undergoes changes in specific factors, relocation of  cytoplasmic organelles and  the post-transcriptional modifications of mRNAs that are essential for fertilization and the preimplantation embryonic  developmental competence.

Perceived benefits of IVM

One of the greatest advantages of IVM is the use of a simpler and less stressful protocol, leading to the reduction of physical hardship to patients, as well as the reduction of time and costs involved for frequent monitoring of follicular development. IVM does not involve long down regulation, and minimal (3 days only) or no hormone injections. This allows a reduced treatment time of about 2 weeks only and no reported side effects.

IVM is extremely safe, especially women who are high responders or women with Polycystic Ovarian Syndrome (PCOS) where the risk of OHSS is virtually eliminated despite the use of human Chorionic Gonadotrophin (hCG) for the final trigger.

The cost of treatment is significantly reduced as the amount of gonadotrophins used is low. For the clinic, the number of visits and admissions due to OHSS is reduced, which also translates to cost savings.

Lastly, in young women undergoing cancer treatment, they frequently lose their fertility potential due to the devastating effects of radiation and chemotherapy. With the advances of anti-cancer treatment, many of these women survive and are desirous of child bearing. It is now possible to cryopreserve oocytes and ovarian tissues, and maturing the oocytes later for use in fertility treatment.  Women face cancer treatment better if they believe they can still have children.

Rationale for the clinical use of IVM

At the current moment, the clinical success rates using IVM are suboptimal. The small cumulus mass of the immature oocyte as well as the increased mobility of the ovary make oocyte recovery more difficult. This leads to lower oocyte collection efficiency. Culture conditions for oocyte maturation and embryo culture has not yet been optimized and for the embryologists themselves, IVM requires more laboratory work. There are also more questions than answers at the moment, such as whether endometrial priming is required, the role of hCG priming or the safety of IVM for the unborn child.

All of the perceived advantages of IVM can only be realized when IVM becomes an efficient means of obtaining a healthy birth. A true measurement of successful oocyte IVM is a complete nuclear maturation, and the ability to fertilize and develop into an embryo that is capable of becoming a live birth.

Selection of patients

Selection of patients for IVM is important. Inclusion criteria includes younger women aged between 18-35 years, with normal ovulatory cycles (26-35 days), Body Mass Index (BMI) between 18-30 kg per metre square, with no endocrine abnormalities and a maximum of  3 previously failed IVF cycles.

Women with polycystic ovaries or Polycystic Ovarian Syndrome (PCOS) are the best candidates for IVM in view of the high number of antral follicles count and the risk of OHSS with conventional IVF. Women who are known to be hyper responders or delayed responders to gonadotrophin stimulation are also suitable. For women who will undergo cancer treatment, their fertility maybe preserved by  vitrification of in-vitro matured oocytes. Collection of such immature oocytes does not delay the commencement of the cancer treatment nor does it require hormonal stimulation which is contraindicated in patients with hormone dependant cancers such as breast cancer.

IVM clinical protocols

There are a diverse number of IVM clinical protocols resulting in a wide range of pregnancy and implantation rates. It is now possible to mature oocytes in-vitro, with maturation rates reaching 75-80%. Clinical pregnancy rates has been reported to be as high as 35-40% per embryo transfer from IVM treatment with an implantation rate of between 10-15%.

There are broadly two main IVM protocols: the Follicular Stimulating Hormone (FSH) stimulated or unstimulated protocols with or without hCG priming.  FSH priming, usually at the beginning of the cycle for three days gives rise to about 33% pregnancy rate and 10-21% implantation rates [6,7]. The effect is unclear but may be related to the increase in size of the follicles and the higher levels of oestradiol. However, in regularly menstruating women, there seemed to be no beneficial effect compared with women with anovulatory PCOS where priming with FSH may improve implantation rate [6].

Luteinizing Hormone (LH) surge occurring in vivo induces oocyte maturation, cumulus expansion, ovulation, luteinisation and possibly follicular atresia. It has been demonstrated that the time course of oocyte maturation in-vitro is hastened and the rate of oocyte maturation is increased by priming with 10 000 IU hCG 36 hours before retrieval of immature oocytes from women with polycystic ovaries or PCOS [8].

Endometrial priming and synchronizing is a critically important part of an IVM cycle. Due to the absence of rising oestradiol and the corpus luteum, exogenous means of preparing the endometrium for implantation is essential. Both oestrogen and progesterone are recommended, the former is usually commenced at time of egg collection and the latter at Day 1 post egg collection.

After the immature oocytes are matured in-vitro for between 24 to 48 hours (usually 28 hours), Intracytoplasmic sperm injection (ICSI) is performed and embryos are transferred two or three days later.

Safety of IVM

To date more than 1000 healthy infants are born from IVM treatment. Only 400 of these were included in registry. There are no reports of congenital malformations attributable to IVM alone [9]. However, early pregnancy losses maybe higher, hence most clinicians may transfer more embryos per cycle.

However, the oldest child born from IVM is only 9 years old and there is a need to conduct more clinical studies to assure the safety of IVM not only in terms of congenital abnormalities but also whether IVM can cause imprinting disturbances.

Conclusion

IVM is becoming an efficient means of treating infertile couples, especially for patients with polycystic ovaries or PCOS. It is still possible to improve IVM success rates through ongoing research in the optimal protocol and culture media. One day, immature oocyte retrieval combined with IVM could possibly replace standard stimulated IVF.

Reference

1. Duckitt K, Templeton AA. Cancer in women with infertility. Curr Opin Obstet Gynecol 1998; 10:199-203
2. Edwards RG: Maturation in-vitro of human ovarian oocytes. Lancet 1965; 2:926-929
3. Cha KY, Koo JJ, Ko JJ, et al. Pregnancy after in vitro fertilization of human follicular oocytes collected from nonstimulated cycles, their culture in vitro and their transfer in donor oocyte program. Fertil Steril 1991; 55:109-113
4. Smith GD. Current Women’s Health Reports 2001; 1:143-151
5. Sherizly I, Galiani D, Dekel N: Regulation of oocyte maturation: communication in the rat cumulus-oocyte complex. Hum Reprod 1988; 3:761-766
6.Mikkelsen AL, Lindenberg S. Benefits of FSH priming in women with PCOS to the in vitro maturation procedure and the outcome: a randomised prospective study. Reproduction 2001; 122:587-92
7. Lin YH, Hwang JL, Huang LW, et al. Combination of FSH priming and hCG priming for in-vitro maturation of human oocytes. Human Reprod 2003; 18:1632-6
8. Chian RC, Buckett WM, Tulandi T, Tan SL: Prospective randomized study of human chorionic gonadotrophin priming before immature oocyte retrieval from unstimulated women with polycystic ovarian syndrome. Hum Reprod 2000; 15:165-170
9. Mikkelsen AL. Strategies in human in-vitro maturation and their clinical outcome. Reprod Biomed Online 2005; 10:593-9

Dr Wong Pak Seng, MOG, MRCOG

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