Middle to lower uterine segment embryo transfer improves implantation and pregnancy rates compared with fundal embryo transfer

OBJECTIVE: To assess differences in pregnancy and implantation rates as a function of the embryo placement. DESIGN: Prospective cohort study. SETTING: A tertiary care center. SUBJECT(S): All fresh, nondonor IVF cycles performed in 2001. INTERVENTION(S): Alteration in embryo transfer (ET) target location from the fundal region to the middle to lower uterine segment. MAIN OUTCOME MEASURE(S): Clinical pregnancy rate (sonographic sac evidence/number of transfer cycles), implantation rate (number of sacs/number of embryos transferred), patient age, peak E(2), and fertilization rate. RESULT(S): A total of 393 fundal and 273 lower to middle uterine segment ETs were performed. The pregnancy (PR), implantation, and birth rates were significantly higher after a middle to lower uterine segment ET compared with fundal ET (39.6% vs. 31.2%; 21% vs. 14%; and 34.1% vs. 26.2%, respectively). Groups did not differ regarding patient age, basal FSH, peak E(2), number of intracytoplasmic sperm injection (ICSI) cycles, fertilization rate, embryo quality, or number of embryos transferred. CONCLUSION(S): Both PR and implantation rates are favorably affected by directing embryo placement to the lower to middle uterine segment. By some unknown mechanism, it appears that this endometrial location provides a more favorable region for embryo deposition.     

胚胎移植位置对体外受精-胚胎移植结局的影响

目的探讨体外受精-胚胎移植（IVF-ET）中,在B超引导下将胚胎移植到子宫腔内的不同位置对妊娠率及胚胎种植率的影响。方法回顾性分析接受IVF-ET治疗的98例输卵管因素不孕患者（共108个周期）的临床资料,根据胚胎移植位置的不同分为两组：A组,胚胎移植到距宫底≥5～〈10mm,共51例患者,56个周期;B组,胚胎移植到距宫底≥10～≤15mm,共47例患者,52个周期。比较两组患者的临床妊娠率、胚胎种植率、异位妊娠率、多胎妊娠率及流产率。结果A组56个周期中,有14个周期妊娠,临床妊娠率为25％,移植胚胎121个,种植17个,胚胎种植率为14％;B组52个周期中,有23个周期妊娠,临床妊娠率为44％,移植胚胎115个,种植28个,胚胎种植率为24％。B组临床妊娠率和胚胎种植率显著高于A组,两组分别比较,差异均有统计学意义（P〈0．05）。两组的多胎妊娠率、异位妊娠率和流产率分别比较,差异均无统计学意义（P〉0．05）。结论在IVF-ET中,胚胎移植位置的不同可影响临床妊娠率和胚胎种植率。     

Selective salpingography: preliminary experience of an office operative option for proximal tubal recanalization

Objective

Embryo transfer (ET) is an important last step during the process of IVF. Over the years much has been learned about the importance of the details of this procedure including the potential impact of transfer depth on outcome. The objective of our study was to evaluate whether transfer depth assessed by air bubble location after ET is associated with clinical outcome.

Study design

Retrospective analysis of the association between transfer distance from the fundus (assessed by air bubble location after ET) and IVF outcome based on cycles (N = 409) of patients with good prognosis undergoing infertility treatment for various indications. Treatments followed standard stimulation, IVF-ICSI and ET procedures. The distance of the air bubble as a surrogate marker of embryo location after transfer was measured and was correlated with implantation (IR) and pregnancy rates (PR) after day 3 and day 5 ET. Univariate comparisons were performed by nonparametric methods and multiple logistic regression was used to further evaluate the association between pregnancy rate and those factors that might influence outcome.

Results

The distance of the bubble was similar in those cycles that led to a pregnancy and those that did not (6.7 vs 6.5 mm; p = 0.48) and PR were comparable when the transfer was in the upper or middle third of the cavity. The IR did not differ when embryos were transferred into the upper, middle or lower third of the uterine cavity. Outcome was analyzed separately based on the day of transfer (cleavage vs blastocyst stage) and the IR did not differ based on the location of the transfer.

Conclusions

Transfer depth does not affect implantation and pregnancy rates when the ET is in the middle or upper third of the uterus.     

胚胎移植技术对体外受精-胚胎移植结果的影响——653例临床分析

目的:分析胚胎移植技术与体外受精后临床妊娠、种植率和继续妊娠率之间的关系。方法:回顾性分析653例新鲜胚胎移植,比较移植情况和临床结果之间的关系。结果:腹部超声引导下胚胎移植后临床妊娠率为47.3%,种植率25.0%,继续妊娠39.7%。移植管顶端位于宫内不同位置以及血染情况不影响结果。8.8%困难移植明显降低种植率(20%比26%),临床妊娠率也降低(35.8%比48.3%),但无统计学差异。结论:腹部超声引导下胚胎移植可以达到较好的临床结果。胚胎放置在宫腔内不同位置以及移植管血染不影响临床结果,但要尽量避免困难移植.     

Embryo implantation rates in oocyte donation: a prospective comparison of tubal versus uterine transfers.

OBJECTIVE: To compare pregnancy and implantation rates in tubal and uterine transfers during a hormonal replacement cycle in an oocyte donation program. DESIGN: Prospective randomized. PATIENTS: Forty-two consecutive patients who entered an oocyte donation program. INTERVENTIONS: Twenty-two patients were assigned for uterine transfer and 20 for tubal embryo transfer (ET). RESULTS: Twenty-three pregnancies were achieved, 12 (54.5%) after uterine transfers and 11 (57.9%) after tubal transfers. Implantation rates in both groups are not significantly different (17.4% uterine transfers versus 21.5% tubal ETs). CONCLUSIONS: Our results suggest that in hormonal replacement cycles (uniform endometrial stimulation) there is no advantage in transferring embryos to the fallopian tube. Furthermore, embryo quality and endometrial receptivity appear to be significantly more important than the time of entrance of an embryo to the uterine cavity in determining its chances of implantation.     

Clinical factors for successful cryopreserved-thawed embryo transfer

Purpose: To study how clinical factors such as embryo quality, cell stage of embryo at cryopreservation, and synchronization of developmental stages between embryo and endometrium at thawing affect the implantation rate after cryopreserved-thawed embryo transfer (ET), these factors were examined in 106 cryopreserved-thawed ETs including 204 embryos. Results: In 86 embryos graded as high quality before transfer by morphological evaluation, 31 implantations were successful, while the other, low-quality embryos did not implant at all. High-quality embryos received less cryoinjury during cryopreservation compared to the injuries sustained by embryos in moderate and poor quality. When cyopreservation was performed at the 1-, 2-, and 3-day cell stages, pregnancies were similarly achieved among most of the embryos at all cell stages. At thawed ETs in natural ovulation cycles, there were some differences among the developmental stages between thawed embryo and endometrium that received the thawed transferred embryos. Although the transfer timelag ranged a day or more, asynchronism of endometrium growth to the cell stage did not reduce pregnancy rates. Conclusions: These results indicated that embryo quality evaluated morphologically was the most important clinical factor for successful implantation of cryopreserved-thawed ET.     

Embryo afterloading: a refinement in embryo transfer technique that may increase clinical pregnancy

OBJECTIVE: Given the importance of ET technique during assisted reproductive technology cycles, we evaluated the effect of embryo afterloading subsequent to placement of the ET catheter on pregnancy rates vs. a standard direct ET. DESIGN: Retrospective cohort analysis. SETTING: University-based assisted reproductive technology program. PATIENT(S): Patients undergoing a fresh nondonor day 3 ET by a single provider over a 1-year period. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Clinical pregnancy. RESULT(S): One hundred twenty-seven patients met inclusion criteria, and the overall pregnancy rate was 46.5%. There was no difference between the two groups with respect to age, basal FSH, or number of embryos transferred. The ET method used was at the discretion of the provider. There was no difference between the two groups in the presence of blood on the transfer catheter. However, there were significantly more transfer catheters with mucus contamination in the direct transfer group (25.58% vs. 5.95%). The clinical pregnancy rate in the group with ET using the afterloading technique was higher than in the direct ET group (52.4% vs. 34.9%). CONCLUSION(S): There was a trend toward an increase in pregnancy rate when an embryo afterloading technique was used. A prospective randomized trial is needed to examine this issue.     

Relationship between peak serum estradiol levels and treatment outcome in in vitro fertilization cycles after embryo transfer on day 3 or day 5

OBJECTIVE: To examine the relationships between peak serum estradiol (E(2)) levels and treatment outcome in in vitro fertilization (IVF) cycles after embryo transfer (ET) on day 3 or day 5. DESIGN: Retrospective analysis of 697 IVF-ET cycles between January 1999 and December 2001. SETTING: A university-affiliated assisted reproduction program. PATIENT(S): Infertile patients undergoing IVF-ET cycles. INTERVENTION(S): Peak E(2) concentration in serum was determined on the day of human chorionic gonadotropin (hCG) administration. The IVF-generated embryos were cultured for 2 days until transfer on day 3. If more than four 8-cell embryos were present on day 3, embryo culture was continued until day 5 for blastocyst transfer. MAIN OUTCOME MEASURE(S): Clinical pregnancy rates. RESULT(S): High peak E(2) levels did not adversely affect treatment outcome. After the cycles were divided according to the day of ET, high peak E(2) levels were associated with improved pregnancy rates after ET on day 5 but not on day 3. CONCLUSION(S): Increasing peak E(2) levels in IVF cycles are associated with improved pregnancy rates after ET on day 5.     

Influence of embryo transfer depth on in vitro fertilization and embryo transfer outcomes

OBJECTIVE: To investigate the influence of transfer distance from the fundus (TDF) on clinical pregnancy rate (PR) and ectopic pregnancy rate. DESIGN: Retrospective cohort. Between January 2000 and December 2001, 699 ultrasound (US)-guided embryo transfers were conducted. Mock transfer was performed to measure uterine cavity depth 1 month before treatment. Cavity depth was measured by abdominal US before the transfer, from the vaginal stripe to the fundus. Transfers were performed with a Wallace embryo transfer catheter (Cooper Surgical, Shelton, CT) using US and physician's judgment of cavity depth. Transfer distance from the fundus was calculated by subtracting the depth of catheter insertion from the cavity depth, as determined by US or by mock transfer. Statistical analyses were performed by building a multivariable logistic regression model to calculate odds ratios and 95% confidence intervals (CI). SETTING: Women aged 23 to 43 years who are in a university-affiliated, community-based IVF program in Springfield, Massachusetts. PATIENT(S): All patients enrolled in IVF program undergoing embryo transfer. INTERVENTION(S): No patient received any additional procedure or intervention. All of the measurements obtained with the embryo catheter and the transvaginal ultrasound were part of the program's protocol for the embryo transfer. MAIN OUTCOME MEASURE(S): Odds ratio examining relationship between embryo transfer depth and PR.Clinical, implantation, and ectopic PR were 37%, 20%, and 2.1%. Cavity depth by US differed from cavity depth by mock by at least 10 mm in >30% of cases. The TDF by US was highly predictive of PR; TDF by mock was not predictive of PR. Increasing the TDF by US resulted in significantly increased PR as well as lower ectopic rates. Using regression analysis, the odds ratio for TDF by US was 1.11 (95% CI: 1.07-1.14). This suggests that for every additional millimeter embryos are deposited away from the fundus, the odds of clinical pregnancy increased by 11%. CONCLUSION(S): After controlling for potential confounders, the clinical PR is significantly influenced by the transfer distance from the fundus. Cavity depth by US is clinically useful to determine the depth beyond which catheter insertion should not occur.     

Blastocyst-stage embryo transfer in patients who failed to conceive in three or more day 2-3 embryo transfer cycles: a prospective, randomized study

OBJECTIVE: To compare blastocyst-stage embryo transfers (ETs) with day 2-3 ETs in patients who failed to conceive in three or more day 2-3 IVF/ET cycles. DESIGN: Prospective, randomized. SETTING: Fertility unit in a university medical center. PATIENT(S): Fifty-four patients with an adequate ovarian response underwent oocyte retrievals. The patients were prospectively and randomly divided into blastocyst-stage and day 2-3 ET groups. INTERVENTION(S): Ovarian down-regulation was obtained using GnRH agonist, and controlled ovarian hyperstimulation was achieved using daily administration of gonadotropins. MAIN OUTCOME MEASURE(S): The rate of blastocyst formation, ET cancellations, pregnancies, implantation, multiple gestation, and live births. RESULT(S): The clinical pregnancy rates per oocyte retrieval were 21.7% and 12.9% per blastocyst and day 2-3 ETs, respectively. Although there was a significantly higher implantation rate for blastocyst embryos (21.2%) as compared with 48- to 72-hour embryos (6%), the multiple-pregnancy rate was not significantly different between both groups. An ET cancellation rate of 26% and 6.4% for blastocyst and day 2-3 ETs, respectively, was observed. The presence of two or more 8-cell embryos on day 3 in culture carried a high probability of obtaining blastocysts for transfer. CONCLUSION(S): This prospective randomized study suggests that in patients with an adequate ovarian response who failed to conceive in at least three IVF/ET cycles [1]. transfer of blastocyst-stage embryos carries a significantly higher implantation rate; [2]. the pregnancy rate per oocyte retrieval and ET are higher in the blastocyst-stage group, even if it did not reach statistical significance; [3]. a higher ET cancellation rate was observed in the whole blastocyst-stage group; [4]. the ET cancellation rate was reduced significantly if the decision to proceed to blastocyst transfer was made on day 3 after oocyte retrieval, which is a post hoc conclusion.     

Location of the embryo-transfer catheter guide before the internal uterine os improves the outcome of in vitro fertilization

The objective of this study was to assess whether positioning the embryo transfer (ET) catheter guide at the time of embryo expulsion, before or beyond the internal os, has an impact on IVF cycle outcome. We performed a retrospective study comparing IVF outcomes in relation to the ET guide position relative to the internal uterine os. We analyzed ultrasound-guided ETs in IVF-intracytoplasmic sperm injection (ICSI) cycles, performed with the tip of the ET catheter guide just before the internal os (group 1) and beyond the internal os (group 2). Implantation and pregnancy rates were significantly better in group 1 than in group 2, at 14.8% versus 11.8% and 57.3% versus 43.1, respectively. We conclude that passing the ET catheter guide beyond the internal os reduces implantation and pregnancy rates.     

全胚冷冻再行解冻胚胎移植周期的临床结局分析

目的:探讨新鲜移植周期与冻融胚胎移植(FET)周期妊娠结局的差异。方法:回顾性分析本中心刺激周期行新鲜胚移植(190例)和全部胚胎冷冻后再行FET(97例)周期的临床妊娠率、种植率以及流产率。结果:190例刺激周期新鲜胚胎种植后的妊娠率、种植率、流产率分别为47.4%(90/190)、30.2%(103/341)、10.0%(9/90),97例全部胚胎冷冻后行FET后的妊娠率、种植率、流产率分别为60.8%(59/97)、47.0%(86/183)、10.2%(6/59),组间妊娠率与种植率均有统计学差异(P<0.05),流产率无统计学差异(P>0.05)。结论:对于有OHSS风险等不适宜进行新鲜胚胎移植的患者,选择全部胚胎冷冻并择期进行FET,并不降低胚胎种植率和临床妊娠率,从而预防迟发型OHSS的发生,可获得更为理想的妊娠结局。     

Transfer and uterine factors are the major recipient-related determinants of success with donor eggs

OBJECTIVE: To define the recipient-related determinants of outcome with donor eggs. DESIGN: Case-control study. SETTING: Community hospital-based assisted reproductive technology (ART) program. PATIENT(S): One hundred thirty-four embryo transfers (ETs) in which two recipients were matched to one donor. INTERVENTION(S): Controlled ovarian hyperstimulation (COH) and ovum retrieval in donors; IVF and ET to recipients. MAIN OUTCOME MEASURE(S): Recipients' age, body mass index (BMI), medical conditions, endometriosis, gravidity, uterine pathology, endometrial thickness, egg number, total motile sperm count, intracytoplasmic sperm injection (ICSI), zygote number, fertilization rate, embryos per ET, embryos frozen, embryo quality, difficulty with transfer, and ongoing pregnancies per ET. RESULT(S): Forty-one recipient pairs had discordant outcomes. Pregnant patients had a lower frequency (9.7% vs. 31.7%, P=.04) and lesser severity of uterine pathology. Endometrium <8 mm was found solely in failed cycles. Pregnant women had fewer moderate or difficult ETs (9.7% vs. 31.7%, P=.04) and more good embryos (1.8 vs. 1.3, P=.03) than the nonpregnant group. CONCLUSION(S): Analysis of recipient pairs with discordant outcomes identifies the recipient-related predictors of success by keeping oocyte quality and the laboratory component constant. Uterine pathology, thin endometrium, transfer difficulty, and number of high-grade embryos are the principal recipient-related determinants of outcome with donor eggs.     

Effectiveness of two-step (consecutive) embryo transfer in patients who have two embryos on day 2: comparison with cleavage-stage embryo transfer

OBJECTIVE: To evaluate the effectiveness, for patients who have only two embryos on day 2, of a two-step (consecutive) embryo transfer (ET) procedure in which a cleaved embryo is transferred on day 2 and a single blastocyst is transferred on day 5. DESIGN: Observational comparative study. SETTING: Private IVF clinic. PATIENT(S): Ninety two-step ET cycles were performed in patients who had two embryos on day 2 (two-step group). Ninety day-2 ET cycles were performed in age- and infertility-matched patients who had two embryos on day 2 (control group). INTERVENTION(S): Cleaved-ET, extended culture of one embryo, and a second transfer of a blastocyst. MAIN OUTCOME MEASURE(S): Implantation and pregnancy rates. RESULT(S): The pregnancy and implantation rates in the two-step group (respectively 33.3% and 17.2%) were significantly higher than those in the control group (18.9% and 9.4%). Thirty-nine of the patients in the two-step group (43.3%) could not proceed to the second step of ET because no viable blastocyst could be obtained, but four of them conceived anyway. CONCLUSION(S): Taking advantage of both day-2 ET and blastocyst transfer, two-step ET may be an effective option for ET in patients who have an insufficient number of embryos.     

Initial IVF-ET experience with assisted hatching performed 3 days after retrieval followed by day 5 embryo transfer

OBJECTIVE: To report our initial IVF-ET experience combining assisted hatching performed 3 days after oocyte retrieval with day 5 embryo transfer (ET). DESIGN: Retrospective review of 110 consecutive IVF cycles not involving donor oocytes, including 16 cycles that involved assisted hatching performed 3 days after oocyte retrieval in combination with day 5 ET. SETTING: Academic teaching hospital IVF center. PATIENT(S): Eighty-six consecutive IVF patients undergoing ET. INTERVENTION(S): Assisted hatching using acid Tyrode's solution performed 3 days after oocyte retrieval in selected cases in combination with day 3 or 5 ETs. MAIN OUTCOME MEASURE(S): Clinical pregnancy rate per ET. RESULT(S): Of the 16 women undergoing day 5 ET following day 3 assisted hatching, 14 had a clinical pregnancy. These included 11 ongoing/delivered singletons and 2 ongoing/delivered twin pregnancies, neither of which was monochorionic. These clinical and ongoing/delivered pregnancy rates compared very favorably with those of 54% and 46%, respectively, for the 35 patients undergoing day 5 ETs without assisted hatching, even though the latter group appeared to be better IVF candidates based on the prognostic factors commonly used to predict success. CONCLUSION(S): Our experience suggests that day 3 assisted hatching followed by day 5 ET may be a useful combination in selected patients. Although not seen in our small series, an increased risk of monochorionic pregnancies remains a theoretical concern when such a combination is used, since both assisted hatching and blastocyst transfers have been independently linked to an increased risk in some reports.     

Transvaginal ultrasound-guided embryo transfer improves outcome in patients with previous failed in vitro fertilization cycles

OBJECTIVE: To determine the effect of transvaginal ultrasound-guided ET in IVF cycles performed on patients who had previously failed to conceive from IVF and compare the results to previous cycles where ultrasound guidance was not used. DESIGN: Retrospective clinical study.Setting: Private practice IVF program. PATIENT(S): One hundred twenty-nine women undergoing consecutive cycles of IVF where fresh embryos were transferred. INTERVENTION(S): Transvaginal ultrasound guidance was used during transfer of embryos. MAIN OUTCOME MEASURE(s): Patient age, number of ampules of gonadotropin used, maximum E(2) level, number of oocytes retrieved, number of two pronuclei embryos obtained, number of embryos transferred, mean embryo score, implantation and pregnancy rate. RESULT(S): There was no difference in any of the clinical parameters measured in IVF cycles resulting in pregnancy when transvaginal ultrasound-guided ET was used compared to the failed cycles when there was no ultrasound guidance. Of the patients who previously had failed IVF cycles and subsequently had IVF cycles with ultrasound guidance, those who became pregnant had higher mean embryo scores than those who did not become pregnant. Overall implantation and pregnancy rates were higher during the study period when transvaginal ultrasound guidance was used than in the previous 3 years when it was not used. CONCLUSION(S): Transvaginal ultrasound-guided ET may be responsible for successful IVF cycles in patients who had previously failed to conceive when embryos were transferred by the clinical touch method. Transvaginal ultrasound guidance may also be responsible for an overall increase in embryo implantation and pregnancy compared to the use of the clinical touch method.     

Is there any difference in pregnancy and implantation rates when nurses perform embryo transfer in an IVF-ET program?

A retrospective analysis of fresh in vitro fertilization treatment cycles and frozen embryo transfer (FET) cycles from mid-1995 to December 31, 1998, was undertaken. Nurses performed embryo transfer (ET) for government-funded cycles, whereas doctors performed ET for self-funded cycles. During the study period, fresh ET was performed in 1,165 treatment cycles. There were no significant differences in demographic data, ovarian responses and the number of embryos replaced between ET cycles performed by nurses and doctors. Pregnancy rates for ETs performed by nurses and doctors were 16.7 and 15.8% per transfer, respectively, whereas the corresponding implantation rates were 8.3 and 6.9%, respectively. Similar pregnancy and implantation rates were encountered in FET cycles whether ET was performed by nurses or doctors.     

Application of atosiban in frozen-thawed cycle patients with different times of embryo transfers

This prospective cohort study aimed to examine the effects of atosiban, given before transfer of frozen-thawed embryo to women with different number of embryo transfer (ET) cycles. Atosiban treatment significantly increased implantation rate and clinical pregnancy rate in the third and more than three ET groups. However, there were no significant increases in the above parameters in the first and second ET groups. Our study showed that patients those who underwent the third or more than three ET cycles were inclined to higher uterine contractions and serum oxytocin level, thus atosiban treatment starting from the third ET cycle may be effective in improving embryo implantation. This is the first study to evaluate the optimal atosiban treatment window corresponding to the number of ET cycles of the patients.     

Impact of retained embryos on the outcome of assisted reproductive technologies

OBJECTIVE: To assess the impact of embryo retention in the embryo transfer catheter followed by "immediate" retransfer on pregnancy outcome in women undergoing assisted reproduction. DESIGN: Retrospective analysis of embryo transfer following in vitro fertilization. SETTING: Assisted reproductive technology practice in a university in vitro fertilization program. PATIENT(S): In vitro fertilization charts for 1,812 embryo transfer cycles representing 1,139 patients between January 1997 and March 2002 were reviewed. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Pregnancy rate, implantation rate, delivery rate. RESULT(S): Three embryo transfer cycles were excluded from analysis because of missing data, leaving 1,364 embryo transfers during oocyte recovery cycles and 445 embryo transfer cycles using thawed embryos. Seventy-one embryo transfers (3.9% of all transfers) were complicated by finding retained embryos after the initial embryo transfer-all retained embryos were immediately retransferred. There was no difference in the frequency of retained embryos during oocyte retrieval versus thawed embryo cycles. The pregnancy, implantation, and delivery rates per embryo transfer were not negatively affected by embryo(s) retained in the transfer catheter. Age, fresh versus frozen embryo, use of ultrasound during the procedure, or transferring physician did not influence pregnancy outcome. CONCLUSION(S): Immediate retransfer of embryos retained in the catheter following the initial transfer attempt did not have an adverse effect on pregnancy outcome.     

Cannulation of a resistant internal os with the malleable outer sheath of a coaxial soft embryo transfer catheter does not affect in vitro fertilization-embryo transfer outcome

OBJECTIVE: To assess the impact of cannulation of a resistant cervical os with the outer malleable sheath of a double-lumen, soft ET catheter on IVF-ET outcomes. DESIGN: Retrospective cohort study. SETTING: University-based IVF center. PATIENT(S): One hundred forty-two patients undergoing 142 ETs. INTERVENTION(S): Trial ultrasound-guided ET at all transfers, leaving the malleable outer sheath in situ when the soft inner catheter could not negotiate the internal os. MAIN OUTCOME MEASURE(S): Implantation rate and clinical pregnancy rate. RESULT(S): In 102 ETs (71.8%), the soft inner sheath easily negotiated the internal os (group 1). Forty ETs (28.2%) required cannulation of resistant internal ora with the outer sheath of the trial catheter (group 2). Implantation rates (35% vs. 32% in groups 1 and 2, respectively) and clinical pregnancy rates (50% vs. 45%) were not significantly different between groups. Blood was present on the transfer catheter after ET more frequently in group 2 than in group 1 (55% vs. 15%); however, neither the implantation rate nor the clinical pregnancy rate were affected by the presence of blood. CONCLUSION(S): Cannulation of a resistant internal os by the malleable outer sheath and blood on the transfer catheter after ET do not have an adverse effect on implantation rate or clinical pregnancy rate.