Approximately one out of six reproductive-aged couples are affected by infertility worldwide. Over time, various assisted reproductive technologies (ART) have evolved, helping couples to overcome fertility problems. Currently, in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI) are the most frequently used ART because of their high success rates. Nevertheless, for some patients, these ART fail and alternative procedures are required. Prior to IVF and ICSI, women must undergo controlled ovarian stimulation (COS) by a series of hormonal treatments to obtain multiple mature oocytes. This results in elevated oestrogen levels, making the techniques inaccessible for certain patients, such as cancer patients requiring immediate treatment, oestrogen-sensitive and pre-pubertal cancer patients, transgender men avoiding gender dysphoria due to female hormone exposures, females at risk of developing ovarian hyperstimulation syndrome, and polycystic ovary syndrome (PCOS) women. Therefore, in vitro maturation (IVM) is investigated as an alternative fertility preservation procedure without the need for COS, making the technique more patient-friendly. In part I of this thesis, different strategies of IVM are considered to preserve fertility in transgender men. Although its high efficiency, 1-3% of ICSI cycles result in fertilization failure (FF). Assisted oocyte activation can overcome FF caused by oocyte activation deficiencies through artificial induction of calcium oscillations, in most cases, using calcium ionophores like ionomycin and calcimycin. Currently, many clinics prefer to use an available CE-marked ready-to-use calcimycin solution. However, an in-house prepared ionomycin solution has been proven of remarkably higher efficiency. Part II of this thesis investigates the efficiency of a novel ready-to-use ionomycin solution for future clinical use.