Knowledge Sharing

2013.01.29

Cytoplasm Transfer

IVF researcher, Lee Women’s Hospital, ZHENG YAN-JUN

With the application of assisted reproduction technology (ART) such as IVF, intracytoplasmic sperm injection (ICSI), embryo coculture system and assisted hatching, the fertilization rate is approximately 30 to 40% for most infertile couples receiving IVF treatment. In other words, many infertile couples have to receive several cycles of treatment to achieve their goal of having a child. Reasons for fertilization failure include failure in ovulation stimulation, poor oocyte or sperm quality, insufficient embryos with good quality for transfer. In addition, theoverall medical standards of the ART center, the quality of medical and nursing staff, and the age, physical constitution, and psychological factors.

For the IVF treatment, researchers have been worked onin vitro culture of embryos so hard to improve the culture environment, but the the cytoplasmic defects of the oocytes or the aging effects have not been able to break through. In 1997, the human pregnancy was announced by Dr. Jack Cohen et al. following the transfer of donor ooplasm into theoocytes of a patient with recurrent implantation failure. This method improved the embryonicdevelopment as well as the implantation rate, and has been used in some infertile couples with outcomes culminated in pregnancy and birth. This technique of introducing small amount of cytoplasm into the oocyte is called cytoplasmic transfer.

Cytoplasmic transfer was successfully developed by Dr. Cohen J., a professor in Santa Barbara University in 1997, and has been used by more than a dozen of reproductive medicine centers around the world to promote embryo development,enhance quality of oocyte for further development, and to improve implantation and pregnancy rate. The procedures are as follows:
 
  1. Collect the oocytes from donors and recipients according to the general IVF procedure.
  2. Collect the sperm from the partner of the recipients.
  3. Place thoroughly washed oocyte and sperm in the micromanipulator.
  4. Aspirate the sperm from the recipient’s partner as well as small amount of ooplasm from the donor.
  5. Microinject the sperm and ooplasm into the recipient’s oocyte.
  6. Transfer the injected oocyte to culture medium, and cultured followed general IVF procedure.
  7. Select well-developed embryos and transfer back into the recipient.
     
In addition to proper oocyte donors, ICSI is also required for ooplasm transfer. This can optimize patient outcomes when strict selection criteria are applied. Proper candidates for ooplasm transfer are listed as follows:
 
  1. Recurrent failure in IVF treatment.
  2. Advanced maternal age, i.e., over 40 years, and experienced failures with IVF.
  3. Abnormal embryonic development after fertilization.
  4. Oocytes with abnormal morphology but intact chromosomes.
     
The baby born from ooplasmic transfer is also called 3P (three-parent) baby because the embryo derived involves oocytes from two females and sperm from one male, i.e., a baby having one father and two mothers. Based on the fact that only part of the cytoplasm from the donor oocyte was transferred to provide better condition of growth of the embryos from fertilization of recipient male and female, the pronuclei from both parents are not affected theoretically, and there is still complete inheritance of chromosome composition from the parents.

Albeit it appears that oocyte with poor qualityto be rejuvenated by ooplasmic transfer, better development and implantation rate was found in the resulting embryo, the so-called nutritious materials from young healthy oocyte donors remains unclear and awaits further investigation. No adverse effects have been reported up to date, although some embryologists remain skeptical. More intensive investigation and follow-up studies are required to support the safety and efficacy of cytoplasmic transfer in assisted reproductive technology.