Embryo transfer and uterine junctional zone contractions. VIDEO (1999)

Embryo transfer is one of the most critical steps affecting the success rate of in-vitro fertilization (IVF) and has changed little since IVF was first described (Steptoe and Edwards 1978). While there is general agreement that a smooth embryo transfer is associated more frequently with successful outcome (Wood et al., 1985; Mansour et al., l990; Visser et al., 1993; Tomas et al., 1998) this opinion is not unanimous (Nabi et al., l997; Tur-Kaspa et al., l998). However, embryos have been found in the vagina following embryo transfer (Poindexter et al., l986; Schulman, 1986) and experimental studies of mock embryo transfer in humans showed expulsion of Methylene Blue in 57% of transfers (Mansour et al., l994) and movement of X-ray contrast medium towards the Fallopian tubes and cervix/vagina in 38 and 21% respectively (Knutzen et al., 1992). Uterine junctional zone (JZ) contractions or endometrial wavelike movements have been characterized in both natural (Ijland et al., 1996, 1997a,b; Kunz and Leyendecker, 1996) and assisted reproduction cycles (Lesny et al., l998b). Recently increased contractility before embryo transfer has been shown to be associated with a lower pregnancy rate (Fanchin et al., 1998). As JZ contractility is minimal and progressively decreases during the luteal phase (Ijland et al., 1996; Lesny et al., 1998b), interference with the endometrium at embryo transfer may change the contraction pattern and affect implantation in a mechanical way. The observation of JZ contractions after mock embryo transfer in oocyte donors (Lesny et al., l998a) provides information about possible treatment outcome. It also demonstrates a connection between the ease of transfer, JZ contractions and mobility of mock embryos in utero. An atraumatic embryo transfer (with a soft end of the catheter, without touching the uterine fundus) did not have any effect on JZ contractility or movement of the mock embryo (Echovist). Difficult embryo transfers (mimicked by touching twice the uterine fundus with soft end of the catheter) generate strong fundo–cervical and random waves in the fundal area which were able to relocate mock embryos towards the cervix and/or into the intramural segment of the Fallopian tube. Contractions were also present when we stimulated uterus with the softer version of the catheter but their effect on mock embryos was to a lesser extent. We chose fundal stimulation because in our opinion it was the most frequent type of stimulus unwillingly given to the uterus at embryo transfer and is not usually considered as a problem. Moreover, we also noted that the application of a tenaculum to the cervix, as occasionally used during embryo transfer to correct the uterine position, could trigger JZ contractions (Lesny et al., 1998c). A further analysis of our 6 years clinical data revealed that an ectopic pregnancy was 3.9 times (95% CI from 1.5 to 10.2) more frequently associated with a difficult embryo transfer than with an easy procedure (Lesny et al., 1998d). In conclusion, the above facts confirm the existence of a mechanical force, which can be one of the decisive factors for embryos to remain in utero. Junctional zone contractions and endometrial wavelike movements of adjacent endometrium can provide an explanation for several clinical facts like lower success rate after difficult embryo transfer or higher ectopic and heterotopic pregnancy rates after IVF–embryo transfer treatment. They also highlight a need for atraumatic embryo transfer without touching the uterine fundus and without manipulation within the cervical area. The benefits arising from using softer catheters or pharmacological assistance at the time of embryo transfer remain to be tested.