Zygote intrafallopian transfer
ZIFT (zygote intrafallopian transfer) is a form of infertility treatment using assisted reproductive technology. The procedure is similar to IVF (in vitro fertilization), but utilizes laparoscopic surgery to place the fertilized egg, called a zygote (Pic. 1), inside a Fallopian tube instead of the uterine cavity like in IVF.
The ZIFT procedure begins similarly to IVF with ovarian stimulation using fertility medications and subsequent egg retrieval. The egg cells are then fertilised in a lab using the sperm of the patient’s partner. Unlike in IVF, where the fertilised egg cells, now called zygotes, are cultured in the lab environment for 3 – 5 days, in ZIFT they are transferred into the patient‘s body within 24 hours. Small laparoscopic surgery (using small incisions in the abdominal wall through which long instruments are inserted) is performed to deliver the zygote into one of the Fallopian tubes (Pic. 2).
After being transferred into the patient’s Fallopian tube, the zygote continues to develop similarly as a naturally fertilised egg cell would. It undergoes cellular divisions (Pic. 1), develops into early stages of the embryo and enters the uterine cavity. In case of successful ZIFT cycle, the embryo lodges in the uterine wall (a process also called nidation) and pregnancy ensues.
If the ZIFT cycle is successful, pregnancy can be detected by pregnancy test usually within two weeks.
ZIFT is most effectively used to treat patients with temporary or permanent blockage of the Fallopian tubes. The surgery used to transfer the zygote allows for placing it past the blockage. However, the standard IVF procedure can be used to similar effect without the need of surgery.
ZIFT has been also suggested as a strategy for patients with repeated implantation failure (RIF). ZIFT offers the appropriate physiological environment for the growing zygote/embryo (avoiding the in vitro culture systems), with an optimal synchronization between embryonic and endometrial development. Moreover, since it prevents intrauterine manipulation and the consequent possible embryo expulsion secondary to sub-endometrial/myometrial contractions, it was also offered to patients with RIF.
A major disadvantage of ZIFT is the requirement of laparoscopy, which poses the risks associated with any surgical procedure. Compared to IVF, ZIFT is considered a more invasive procedure.
ZIFT has also been associated with an increased risk of twins or multiplets, as two or more zygote have been usually transferred. Carrying multiple embryos in turn increases the risk of adverse pregnancy outcomes, such as miscarriage, and other complications.
Studies have shown increased risk of ectopic pregnancy (Pic. 3) in ZIFT cycles compared to to IVF cycles with embryo transfer. This may be caused by the direct transfer of zygote into the Fallopian tube, which increases the risk of implantation directly into the tubal wall. Ectopic pregnancy is a potentially life-threatening complication of pregnancy, when the embryo implants in other localization than the uterine lining, most commonly in the wall of the Fallopian tube. The developing embryo burrows into the tubal wall and invades blood vessels, which leads to abdominal pain and bleeding. Sometimes, the bleeding can be severe enough to threaten the woman’s life. In cases of less advanced ectopic pregnancy, the administration of the drug methotrexate may be sufficient for treatment. When the tube has ruptured, surgical intervention is required.
The success rate of ZIFT cycles varies greatly. The outcome is influenced by the couple’s age and associated health issues. Average success rate of a ZIFT cycle is approximately 20%.
However, as IVF cycles have shown similar or even better results than ZIFT and do not require an invasive laparoscopic procedure, the procedure has become increasingly rare and constitutes less than 1% or assisted reproduction technology procedures.