A critique to optimizing and factors associated with Embryo Transfer Success

Embryo transfer is arguably the most critical step in assisted reproduction. Various modifications have been suggested to optimize embryo transfer (ET) during assisted reproduction in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). To review the different aspects of the procedure in the light of recent evidence; However, not all of these modifications have been evaluated by randomized controlled trials (RCTs). The evaluation of these modifications by taking an evidence-based approach, Meta-analyses and RCTs have shown that the pregnancy rate is significantly increased by performing a dummy ET before the actual transfer, by ultrasound-guided ET, and by depositing the embryos 2 cm below the uterine fundus. Similarly, meta-analyses and RCTs have shown that bed rest after ET, flushing the cervical canal before ET, sexual intercourse around the time of ET, use of a fibrin sealant, use of a soft catheter as opposed to a rigid catheter, and slow withdrawal of the catheter after ET did not affect the pregnancy rate.

The value of removing the cervical mucus prior to ET, performing ET with a full bladder, avoiding the use of a volsellum, and routine administration of antibiotics following ET remains to be studied by RCTs. Randomized trials have shown that significantly higher pregnancy rates are obtained when embryo transfer is performed under ultrasound guidance, the embryos are deposited in the middle part of the uterine cavity, an atraumatic technique is used and when low-dose aspirin is routinely administered following the procedure. Blood in the catheter and leaving the embryos inside it for more than 120 s diminish the pregnancy rate significantly. Air in the catheter, immediate removal of the catheter, performing two transfers in the same cycle, prolonged bed rest, sexual intercourse after embryo transfer or the use of sildenafil do not affect the results.

Based on currently available evidence, Cochrane reviews have concluded that the live birth rate is not increased by delaying embryo transfer from day two to three or to the blastocyst stage and that single embryo transfer leads to lower live birth rates than the transfer of two embryos. The value of a mock transfer a few days before the actual procedure has been challenged as the position of the uterus may change. The effect of holding the cervix with a volsellum, routinely administering antibiotics and the superiority of one catheter over the others is still to be determined.

The success rate after treatment by in-vitro fertilization (IVF) depends on variables that falls into two mutually exclusive categories:

1.       The characteristics of the couples being treated

2.       The performance of the clinic. The clinicians' roles are mostly limited to stimulation, oocyte collection and embryo transfer.

There are some Factors associated with embryo transfer success:

·         Removal of hydrosalpinges: Researchers agree that this is the most important factor. The presence of hydrosalpinx has a negative effect on IVF/embryo transfer, possibly due to embryo toxicity and harmful effects on the endometrium’s ability to receive the embryo.

·         Absence of bleeding: The presence of blood on the catheter is usually the sign of a difficult transfer.

·         Type of catheter used: Various catheters are used for embryo transfer, differing in terms of rigidity, girth and overall shape.

·         Not touching the fundus: Since embryo transfer is often a blind shot, contact between the catheter and the uterine walls may result in trauma.

·         Avoiding the use of a tenaculum: Similar to complications such as bleeding, tenaculum usage reflects the difficulty of the transfer.

·         Removal of the cervical mucus plug: The amount of mucus to be removed, the method used, as well as whether it should be removed at all is still a point of debate.

·         Ultrasound details of uterine cavity before treatment: Ultrasound allows the fertility specialist to visualize any anomalies in the uterine cavity before starting the transfer, and allows for better preparation for the procedure.

·         Keeping catheter stationary for at least one minute: This practice may be more of a cautionary measure to mitigate trauma or prevent irritation.

·         30 minutes rest after transfer: When IVF was first implemented; patients had to rest flat on their backs for 24 hours after the procedure. Embryo transfer has since evolved into an outpatient procedure, with most women having only a few minutes rest. Recent research suggests that bed rest for 30 minutes was not important, and extended bed rest after embryo transfer does not affect pregnancy rates.

·         Dummy transfer before treatment: The role of ‘mock embryo transfer’ is generally considered unrelated to the success of the actual embryo transfer.

·         Ultrasound-guided transfer: Ultrasound guidance during embryo transfer improved the placement of the catheter tip with respect to the endometrial surface.

·         Giving anti prostaglandins to prevent contractions: The insertion of a Cannula into the uterus may cause contractions, and can hinder implantation.