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on the catheter, once it is withdrawn, is associated with implantation or pregnancy rates. (Grade C)
Does the Rate of Injection of the Catheter Load Affect Pregnancy and Live-birth Rates?
The ideal speed at which the embryo should be injected at the time of embryo transfer is unknown, as this may be one of the most difficult aspects to quantify and thus compare. The earliest attempt at assessing the ideal veloc- ity of injection was in 2003 when a computational model suggested that high injection speeds may lead to ectopic pregnancies (122). This hypothesis was corroborated by several studies using both mathematical and simulated in vitro models. These studies all suggested that the injec- tion velocity of the embryo could impact the trajectory of the placement, and therefore potentially impact implanta- tion rate and the risk of ectopic pregnancy if a fast speed was used too near the fundus (123–126). A 2012 simulation study assessed standardization of injection speed by evaluating a pump-regulated embryo transfer (PRET) device compared with manual injection. The PRET device generated reliable and reproducible injection speeds, whereas manual injection showed large variation in speed even with a standardized protocol (127). A non- blinded randomized trial also utilizing the same PRET device resulted in less variance in embryo positioning as assessed by ultrasound measurement compared with manual injection (128).
Summary statement:
Given the paucity of data, there is insufficient evidence to recommend any specific injection speed of the cath- eter at the time of embryo transfer. (Grade C)
Do Retained Embryos in the Transfer Catheter and Immediate Re-transfer of Them Affect Implantation, Clinical Pregnancy, or Spontaneous Abortion Rates?
Retained embryo(s) after the initial transfer attempt is an un- common, but clinically worrisome event, creating anxiety for patients and practitioners. The majority of studies addressing this question report an incidence of retained embryo(s) of <3%; however, three studies reported rates of 5%, 7.5%, and 10%, respectively (106, 121, 129).
The nature of this problem precludes an RCT. All pub- lished studies report an immediate re-transfer and retrospec- tive analyses of this variable. The evaluated data include 12 studies (secondary outcome of 1 RCT, 10 cohort studies, 1 se- ries) (85, 106, 107, 111, 121, 129–135). In all but one report, the clinical outcomes of implantation, clinical pregnancy, and spontaneous abortion rates were statistically unchanged for patients undergoing re-transfer after embryo retention. That study reported a statistically significant decline in implantation rate from 17% to 13% (P1⁄4.03) after 29/584 re-transfers of embryos at either the cleavage or blas- tocyst stage. There was no statistical difference in clinical pregnancy rate (106).
Summary statement:
There is fair evidence based on the secondary outcome of one RCT, nine cohort studies, and one series that re- tained embryos in the transfer catheter and immediate re-transfer do not affect implantation, clinical preg- nancy, or spontaneous abortion rates. (Grade B)
Does Bed Rest or Ambulation Affect IVF-Embryo Transfer Pregnancy and Live-birth Rates?
Among the many empiric practices of embryo transfer that have been scrutinized by studies designed to improve IVF suc- cess rates, bed rest has emerged as a prime candidate to study. In particular, a number of studies were designed to focus on the duration of time patients remained at bed rest following the transfer of embryos into the endometrial cavity. During the early years of IVF compared to recent times, the longest variations of time that patients were kept supine existed in hopes of avoiding uterine contractions and ‘‘premature expul- sion’’ of embryos from the uterus. Anecdotal reports have included durations of bed rest for many that extended up to 24 hours and for some as long as 2 weeks.
Of 14 studies included from this systematic literature re- view, none of them demonstrated a benefit of bed rest of any duration. Three RCTs between 1997 and 2004 included 712 patients randomized to different periods of bed rest and showed no benefit of any of the following durations: 1 hour vs 24 hours (N1⁄4378), 20 minutes vs 24 hours (N1⁄4182), and immediate ambulation vs 30 minutes (N1⁄4152) (136–138). One additional RCT randomized 120 patients to either bed rest for 15 minutes or immediate ambulation and followed outcome of the air bubbles in the endometrial cavity by ultrasound, demonstrating no difference between the two groups (139). Three systematic reviews (N1⁄4 724; N1⁄4542; N1⁄4757, respectively) (140–142) corroborated the findings of these RCTs. Furthermore, three cohort studies (143–145) (N1⁄4677) and two patient series (146, 147) (N1⁄4112) demonstrated that bed rest of different durations did not benefit pregnancy outcomes. One additional series followed the endometrial air bubbles with ultrasound in patients who stood up immediately after transfer and found a similar position of the air bubbles before and after standing, concluding that for these 101 IVF cycles ‘‘standing shortly after embryo transfer does not play a significant role in the final position of embryo-associated air.’’ (148).
In contrast to the studies that have shown no benefit, one well-designed recent RCT demonstrated possible harm (149). Two hundred-forty patients undergoing their first IVF cycle were randomized to either 10 minutes of bed rest or immedi- ate ambulation. This study demonstrated that the live-birth rates were significantly (P1⁄4.02) higher in the no bed rest group (56.7%) when compared to 10 minutes of rest (41.6%). Given that this study was performed in recent years benefiting from more current success rates, used a more ho- mogeneous patient population of first-time IVF cycles with similar demographic and cycle data between the two groups, and demonstrated a statistically significant lower success rate for the relatively short duration of bed rest of 10 minutes, the suggestion of harm for bed rest is noteworthy.
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