As part of the initial infertility physical exam, cervical aberrations may be noted. Cervical factors that may affect a successful embryo transfer may include copious cervical mucus, cervical stenosis, acute cervico-uterine angulation, or anatomical distortion of the cervix to a hard-to-visualize position, such as the anterior vaginal surface. Regardless of the anomaly, passage through the cervix is required for successful transcervical embryo transfer.

It is likely that the easiest cervical challenge to tackle, cervical mucus, if not addressed, has the ability to plug the tip of the ET catheter, thereby making it difficult to gently transfer the embryos to the endometrial cavity, especially since they are transferred in a small volume of culture media. Beyond plugging the ET catheter, it is possible that cervical mucus may be introduced into the uterine cavity along with the catheter and this may affect implantation. In the same regard, if the embryos adhere to the cervical mucus, they may be dragged out of the uterus upon removal of the ET catheter. In fact, the presence of mucus on the catheter tip has been associated with a significantly higher incidence of retained embryos [15, 16]. Along the same lines, blood found outside, but not inside, the transfer catheter after ET is associated with lower rates of embryo implantation and clinical pregnancy although this is likely not related to the same mechanism as cervical mucus and instead, is related to a traumatic ET [17].

In a prospective study by Mansour et al. [18], methylene blue dye was used as a surrogate for culture media in a mock embryo transfer model. As part of their study, the patients underwent mock ET twice, before and after aspiration of the cervical mucus. Their results demonstrated that the dye was extruded at the external os in 57 % of the cases when the cervical mucus was not aspirated compared to 23 % when the mucus was aspirated, a statistically significant difference [18].

In a retrospective analysis of patients undergoing a day 3 ET by a single provider, it was found that by using an embryo afterloading technique, the researchers had a higher clinical pregnancy rate as compared to standard direct ET (52.4 % vs. 34.9 % respectively) [19]. In the embryo afterloading technique, an empty embryo transfer catheter was passed into the lower uterine segment under ultrasound guidance, the inner sheath was slowly removed, and a second inner sheath with the embryos was threaded into the inner sheath into the catheter. The authors postulate that the embryo afterloading technique may result in higher pregnancy rates by preventing mucus contamination/plugging, since there were significantly more transfer catheters with mucus contamination in the direct transfer group (25.58 % vs. 5.95 %) [19].

Furthermore, cervical mucus has been found to be a possible source of bacterial contamination of the endometrial cavity and the embryos [20–22]. In a prospective study of patients undergoing transcervical embryo transfer, microbiological cultures were performed on endocervical swabs and embryo transfer catheter tips. The authors found positive microbial growths from endocervical swabs in 70.9 % of patients and from catheter tips in 49.1 %. The clinical pregnancy rates were 57.1 % in the group of patients without growth and 29.6 % in the group with positive microbial growth from catheter tips [20]. In another study, it was found that the clinical and ongoing pregnancy rates as well as implantation rates were significantly lower in those who had positive versus negative cultures from the tips of the mock embryo transfer catheters immediately prior to embryo transfer (24 % vs. 37 %, 17 % vs. 28 %, and 9 % vs. 16 %, respectively) [21]. The authors reported that the positive cultures were predominantly Escherichia coli (64 %) and Streptococcus species (8 %). Selman et al. [22] conducted a study where separate samples were collected for microbial examination from the following sites: the fundus of the vagina, the cervix, the embryo culture medium prior and post embryo transfer, the tip of the catheter, and the external sheet. All the samples were separately cultured to identify any bacteria or yeast present. They found that the pregnancy rates were significantly lower in only patients testing positive for Entrobacteriaceae and Staphylococcus species [22]. Taken together, the literature supports aspiration and removal of all visible cervical mucus.

Upon initial inspection of the cervix, it may be noted that the cervical os is either punctate or even difficult to visualize. Cervical stenosis may be congenital, iatrogenic, or secondary to infection, cervical trauma, endometriosis, or postmenopausal atrophy. The classic description of cervical stenosis is a narrowing of the cervical canal to less than 2.5 mm; stenosis of the visible external cervical os has been described as an external os diameter less than 4.5 mm or roughly the size of a cotton-tipped applicator [23, 24]. In patients who have had a laser cone biopsy, there has been a reported incidence of postprocedural cervical stenosis in 17 % of patients within 3–5 years [25]. This is compared to an approximate 10 % risk after a cold knife conization or 4–19 % incidence after a loop electrocautery excision procedure (LEEP) [26–28]. Due to the newly updated American Congress of Obstetricians and Gynecologists cervical cancer screening guidelines and vaccination against HPV, fewer women are having destructive cervical procedures, and as a result, iatrogenic cervical stenosis frequency should diminish. However, since the IVF patient population is an older population, it is possible that many of these women underwent a cervical procedure prior to the changes in the guidelines [29].

Although the cervix may appear stenotic, it is possible that the uterine sound may be able to traverse the os; therefore, it is our program’s policy that the trial transfer be attempted on all visually abnormal cervices in those patients undergoing a future ET. In the event that either the catheter cannot pass through the stenotic external cervical os or the os cannot be clearly identified, the patient should return to the office at the time of menses since the origin of the menstrual blood may help identify the cervical os. In some cases, the patient may warrant surgical intervention either prior to initiation of COH/recipient synchronization or, if absolutely necessary, at the time of oocyte retrieval.

While some authors have advocated for dilation of the cervix at the time of oocyte retrieval given that the patient is already under anesthesia and does not have to come to an additional procedural visit, both Visser et al. [15] and Groutz et al. [30] found that a short interval between dilation and embryo transfer has resulted in poor pregnancy outcomes [15, 30]. This may be due to the fact that the endometrium does not have sufficient time to recover from any trauma, inflammation, or bacterial contamination caused by the dilation [4]. However, Abusheikha et al. [31] evaluated the effects of cervical dilation, performed approximately 2 weeks before embryo transfer and found that of those women who failed to conceive after a prior embryo transfer, nearly 37 % achieved a pregnancy [31]. Therefore, it is advisable to perform cervical dilation prior to initiation of COH/recipient synchronization.

Typically, we manage cervical stenosis with mechanical dilation under monitored anesthesia care (MAC) or “conscious” sedation. As has been previously described, the patient is brought to the operating room with a full bladder, she is placed in dorsal lithotomy position, a speculum is placed, the upper lip of the cervix is grasped with a single-toothed tenaculum, and the cervix is mechanically dilated under transabdominal ultrasound guidance starting with a lacrimal duct probe to ensure that a false passage is not created [32–34]. In the event that the cervix is indistinct or flush against the vagina, a sponge stick can be used to manipulate the uterus with sonographic confirmation. At this point, a tenaculum can be used to grab any remnant of cervical tissue, or as described by Valle et al. [35], the vaginal apex and the cervix can then be probed with a lacrimal dilator; again, transabdominal ultrasound should be used to confirm entry into the endometrial cavity before sequential dilation [35].

Some authors advocate for preoperative prostaglandin (misoprostol) or antiprogestogen (mifepristone) administration in those patients who are anticipated to have a challenging cervical dilation. Misoprostol can be administered orally or vaginally in doses ranging from 200 to 400 mcg. In a systematic review of the literature, Polyzos et al. [36] found that premenopausal women treated with misoprostol had a significantly lower risk for further cervical dilation in the diagnostic setting and a significantly lower risk for cervical laceration in the operative setting when compared with placebo [36]. In addition, the mean cervical width prior to hysteroscopy was significantly higher in premenopausal women treated with misoprostol compared with placebo [36]. In contrast, Cooper et al. [37] also conducted a systematic review of the literature and found that prostaglandin administration conferred no benefit with respect to the pain experienced during cervical dilation and there was only some evidence that misoprostol reduced the amount of force and requirement for dilation of the cervix beyond 5 mm [37]. The authors go on to state that preoperative mifepristone did not have any significant effect on the pain experienced during the procedure or dilation of the cervix [37].

Previous authors have described hysteroscopic endocervical resection or cervical shaving as means of creating a distinct and compatible cervical canal. Wortman and Daggett [38] described a method whereby hysteroscopic endocervical resection was used to create a portal of entry to the endometrial canal for women undergoing a hysteroscopic myomectomy [38]. In their model, they reconfigured the contours of the surgical electrode of a standard hysteroscope. Of the 33 patients that were treated, entry into the endometrial cavity was achieved in all cases without any demonstrable complications [38].