The alternative to egg donation? Nuclear and spindle transfers for women with embryo development problem

Assisted reproductive methods can be performed to help pregnancy. However, some fertility problems need extraordinary solutions. Embryo development problems are one such case.. Is there any other option available? What techniques, apart from egg donation, may ensure the possible positive outcome of the IVF treatment? During this webinar, Birol Aуdin, a leading clinical embryologist and head of embryology laboratory at IVMED , talked about an interesting alternative to egg donation: nuclear and spindle transfer for women with embryo development problems.

Everything is about egg quality

Birol Aуdin admits that poor egg quality is one of the main causes of repeated assisted reproduction treatments. The quality of the eggs is mainly determined by small organelles named mitochondria (the energy suppliers of the cells), together with other factors present in the cytoplasm of the eggs. Patients who are dealing with poor egg quality can experience multiple IVF failed attempts due to the impaired embryo development and have to be treated with conventional egg donation programmes to be able to have a child. The causes of poor egg quality can be different. They include maternal age (the older the woman, the lower the quality), PCOS (polycystic ovary syndrome – recognised in 5%-10% of women nowadays), low ovarian reserve (connected with maternal age, PCOS and endometriosis), genetic factors and endometriosis. One of the reasons is also mitochondria in an egg cell break down affected by the lack of the energy for the egg.

Egg donation alternative needed?

Mitochondria degeneration will decrease a woman’s chances of getting pregnant. They start to get mutations in their DNA and that lack of energy doesn’t allow embryos to sustain fertilisation. If doctors are able to stop the mitochondrial degeneration from happening they will have a chance to repair nuclear function inside of the oocyte. Birol Aуdin stresses that each couple have a social and genetic right to both have a child and carry up their genetic material during pregnancy. Egg donation seems to be an easy alternative to achieve pregnancy but it involves a lot of psychological and ethical aspects, too. Aspects which are not always considered by doctors but by patients themselves. So what are the alternatives for egg donation? According to Birol Aуdin, there are two solutions: spindle transfer and nuclear transfer. During cell division, chromosomes in the cell can be shared equally because of the spine. Spindle has a very important role foe the cell division and for the genetic potential of the egg. However, it is quite difficult to determine the spindle in the egg cell. It is only possible by special software and the polarisation system on the microscope. Spindle view system is used in a still limited number of clinics nowadays as it requires experienced specialists and high financial investments.

The mystery of spindle transfer revealed

Spindle transfer is described as the replacement of the entire cytoplasm of poor quality eggs. The procedure is based on transferring the egg spindle (containing the genetic material) from an affected woman into donor eggs with healthy cytoplasm. Prior to that, the donor’s eggs have their spindle removed. The eggs resulting from that procedure have their cytoplasm repaired and can be inseminated by conventional techniques (ICSI) with the sperm of the woman’s partner. The embryo develops in vitro and is then transferred to the womb of the woman who will carry the child. Spindle transfer has the unquestionable advantage: it gives the intended parents the chance to have a child that is genetically related to them. However, Birol Aуdin says that genetic continuity is not the only advantage of spindle transfer. It may also give families affected by a serious and life-limiting mitochondrial disease the chance of having healthy children. The study suggests that in the US alone 770 babies could be saved from these diseases annually. Maternal spindle transfer tested on human eggs led to the development of blastocysts and has proved to cause less mechanical and morphological damage during the manipulation.

Pronuclear transfer and its advantages

Pronuclear transfer (PNT) is about performing in vitro fertilisation using the eggs of the affected woman whose mitochondria DNA contains mutant mtDNA, and the sperm of the father. Thanks to the subsequent extraction of the pronucleus on day 1 of the development, most of the mutated mitochondria is left behind. These pronuclei are then transferred to an enucleated zygote with healthy mitochondria. The hybrid zygote is developed in vitro until it reaches the appropriate state for the transfer to the uterus. According to Birol Aуdin, advantages of pronuclear transfer are not to be ignored. Firstly, there is no risk of fertilisation as the transfer takes place already between zygotes. The blastocyst outcome is better and the families affected by mitochondrial diseases get the chance to have healthy offspring. Summing up: both spindle and nuclear transfer are innovative techniques that require extensive specialist experience on the part of the medical staff and special cultivation methods during manipulation. However, their advantages and new hope they give to many people struggling with infertility are not to be underestimated.