An introduction to in vitro maturation

This review explained the process and success rates of in vitro maturation, an assisted reproductive technique that can avoid the risk of ovarian hyperstimulation syndrome.

Assisted reproductive techniques, such as in vitro fertilization (IVF) generally involve the use of hormones to stimulate the ovaries and control the timing of ovulation. When follicles (eggs) have matured, they are harvested from the ovaries and fertilized outside of the body. However for many women, particularly those with polycystic ovarian syndrome, these hormonal treatments can lead to ovarian hyperstimulation syndrome. This causes painful, swollen ovaries, and in some cases can cause a dangerous increase of fluid in the abdomen and chest.

In vitro maturation is a recently developed procedure that can decrease the risk of ovarian hyperstimulation syndrome, by harvesting immature eggs, therefore avoiding the need for ovarian stimulation. Eggs are then matured and fertilized outside of the body. This review discusses the process of in vitro maturation and which patients would benefit most from this procedure. 

In vitro maturation is most often used in women with polycystic ovarian syndrome, who are at high risk for ovarian hyperstimulation. However, recent studies have shown that it can be successful in women who ovulate normally as well. The most important feature of a potential patient is the follicle count, or the number of eggs available in the ovaries, as eggs must be available for harvesting. Women with polycystic ovarian syndrome often have very irregular cycles, and may need hormonal treatments to induce menstruation and start a new ovulation cycle; women who ovulate normally can undergo regular ultrasounds to determine the optimal time for harvest.

Follicles are harvested when they reach 12-14 mm in size, and are then matured and fertilized outside of the body. The fertilized eggs are then inserted into the uterus, just as in traditional IVF. Because it is essential for the uterus to be receptive in order for the fertilized egg, or embryo, to implant, patients take supplements of the hormones estradiol and progesterone until the 10th week of pregnancy.

Miscarriage rates have been found to be significantly higher with in vitro maturation compared to IVF, though some studies have suggested that this association may be due to polycystic ovarian syndrome rather than the procedure itself. One clinic reported implantation rates of 15% and clinical pregnancy rates (a positive pregnancy test) of up to 40%, with similar rates of success in women with normal ovulation. It is estimated that roughly 400 children have been born through in vitro maturation, and there is little evidence of any adverse developmental effects in these children.

In vitro maturation is also beneficial for women who over-respond to ovarian stimulation, which is defined as more than 20 maturing follicles in an IVF cycle. This would normally be cause for cancellation of the cycle, as triggering ovulation in these women could lead to ovarian hyperstimulation syndrome. Studies have shown that harvesting both mature and immature follicles in over-responding patients can lead to successful fertilization 82% of the time, and a 46% pregnancy rate.

In vitro maturation can also be helpful for women who do not respond to the hormonal treatments necessary for IVF and women who need to preserve their fertility before undergoing chemotherapy.

This review concluded that in vitro maturation is an effective assisted reproductive technique, particularly for women with polycystic ovarian syndrome who are at risk of ovarian hyperstimulation syndrome.