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

Previous tubal ectopic pregnancy raises the incidence of repeated ectopic pregnancies in in vitro fertilization-embryo transfer patients

PURPOSE

To investigate the incidence of Tubal Ectopic Pregnancies (TEP) in IVF-ET patients with respect to the status of the fallopian tubes after a previous TEP.

MATERIAL AND METHODS

This retrospective study compares patients undergoing 481 IVF-ET cycles after conservatively or surgically treated TEP(s) with a Control Group (idiopathic or male factor for IVF-ET indication). Medical reports of surgery and/or hysterosalpingograms prior to the IVF cycles classified the status of the fallopian tubes.

RESULTS

12 TEPs (8.95%/Pregnancies (PR)) occurred in the Study Group. In the Control Group one TEP (0.75%/PR; p < 0.001) was found. Smoking increased the probability of TEPs (p = 0.0028) and of pathological pregnancies (abortion, biochemical and ectopic PR; (p = 0.0411)). For statistic evolution logistic regression (PROC GENMOD) and a repeated measure model were applied.

CONCLUSION

Women with a previous TEP should be informed about the significantly increased risk for a further TEP in IVF-ET treatment, especially if they are smoking.

Unruptured ovarian pregnancy following in-vitro fertilization: Missed diagnosis followed by successful laparoscopic management

Ovarian pregnancy after in-vitro fertilization is rare and can be easily missed unless there is a high index of suspicion. Here we present such a case which was missed initially but was later successfully managed laparoscopically.

Does the timing of mock embryo transfer affect in vitro fertilization implantation and pregnancy rates?∗

The timing of a mock embryo transfer does not affect in vitro fertilization implantation or pregnancy rates. Performing a mock embryo transfer at the time of oocyte retrieval, 3 to 5 days before embryo transfer, does not have a deleterious effect on the endometrium.

The position of transferred air bubbles after embryo transfer is related to pregnancy rate

OBJECTIVE

The possibility to visualize the transfer air bubbles is one of the main benefits of ultrasonographic-guided embryo transfer. The objective of this study was to analyze the relation between the position of the air bubbles and pregnancy rates.

DESIGN

Prospective data-analysis.

SETTING

University fertility clinic.

PATIENT(S)

IVF and intracytoplasmic sperm injection patients.

INTERVENTION(S)

Transabdominal ultrasonographic guidance at embryo transfer.

MAIN OUTCOME MEASURE(S)

Pregnancy rate, length endometrial plate, distance catheter to fundus, distance air bubbles to fundus.

RESULT(S)

Analysis of 367 consecutive ultrasonographic-guided embryo transfers following IVF or intracytoplasmic sperm injection treatment. Both absolute and relative position of the air bubbles were significantly closer to the fundus in patients who became pregnant compared with patients who did not become pregnant. When the relative position of the air bubbles was in the fundal half of the endometrial plate pregnancy rates were significantly higher compared with the lower half of the endometrial plate, 43.0% and 24.4%, respectively, P=.002. Multiple regression analysis revealed the relative position as an independently associated determinant for pregnancy.

CONCLUSION(S)

The position of the air bubbles after embryo transfer is related to pregnancy rate; the highest pregnancy rates are found when the air bubbles end up closer to the fundus.

Ovarian pregnancy after in vitro fertilization

We report a rare ovarian pregnancy after in vitro fertilization and transcervical embryo transfer. Ultrasound guidance of embryo transfer does not eliminate the risk of this potentially lethal complication.

Air bubble migration is a random event post embryo transfer

INTRODUCTION

Air bubble location following embryo transfer (ET) is the presumable placement spot of embryos. The purpose of this study was to document endometrial air bubble position and migration following embryo transfer.

DESIGN

Multicenter prospective case study.

MATERIALS AND METHODS

Eighty-eight embryo transfers were performed under abdominal ultrasound guidance in two countries by two authors. A single or double air bubble was loaded with the embryos using a soft, coaxial, end opened catheters. The embryos were slowly injected 10-20 mm from the fundus. Air bubble position was recorded immediately, 30 minutes later and when the patient stood up.

RESULTS

Bubble marker location analysis revealed a random distribution without visible gravity effect when the patients stood up. The bubble markers demonstrated splitting, moving in all directions and dispersion.

CONCLUSION

Air bubbles move and split frequently post ET with the patient in the horizontal position, suggestive of active uterine contractions. Bubble migration analysis supports a rather random movement of the bubbles and possibly the embryos. Standing up changed somewhat bubble configuration and distribution in the uterine cavity. Gravity related bubble motion was uncommon, suggesting that horizontal rest post ET may not be necessary. This report challenges the common belief that a very accurate ultrasound guided embryo placement is mandatory. The very random bubble movement observed in this two-center study suggests that a large "window" of embryo placement maybe present.

Assisted hatching is more effective when embryo quality was optimal in previous failed IVF/ICSI cycles

Assisted hatching (AH) was developed as a possible solution to repeated implantation failure. The aim of this analysis was to examine the relationship between the morphology of embryos in a previous cycle on outcome in a subsequent cycle with AH. A total of 175 AH cycles performed after previous failed ART without hatching were divided into group A with optimal and group B with suboptimal embryos transferred previously. The groups were similar in terms of demographic and cycle characteristics. In group A, there was a significant improvement (p<0.001) in implantation (28.8 vs 5.1%), clinical pregnancy (41.9 vs 12.1%) and live birth rate (38.5 vs 8.6%) compared with group B. The data suggest that the prognosis for treatment is better if AH is performed after failure despite optimal embryos compared with failure associated with suboptimal embryos and embryo quality is the most significant factor affecting outcome.

The influence of abdominal ultrasound-guided embryo transfer on pregnancy rate: a preliminary report

To determine whether the use of abdominal ultrasound-guided embryo transfer improves the clinical pregnancy rate in patients undergoing in vitro fertilization, 50 fresh cycles with day 3 embryo transfer were studied; 27 patients were randomized to ultrasound-guided transfers, and 23 patients were randomized to clinical touch transfers. Although the clinical pregnancy rate was not statistically different (18.5% in the ultrasound-guided group vs. 17.4% in the clinical touch group), the use of abdominal ultrasound during the embryo transfer procedure provided a greater degree of confidence and satisfaction to both patients and physicians.

Bioengineering Studies of the Embryo Transfer Procedure

Embryo transfer (ET) is the final manual intervention in extracorporeal fertilization in which an embryo is transferred into the uterus by a transcervical catheter. The low rates of embryo implantation within the uterus are attributed, among other factors, to the ET technique, which depends on a multitude of anatomical, physiological, and mechanical aspects. We developed computational and experimental models to simulate ET to examine the contribution of mechanical features to the success of this procedure. The experimental model allowed laboratory simulations of the dispersion of the catheter load as a result of different injection speeds into a tilted uterine model. The mathematical model analyzed potential trajectories of the transferred embryos resulting from the interaction between the injection velocity and the intrauterine flows caused by uterine peristalsis. The simulations revealed the important contribution of mechanical parameters, such as the position of the uterus and the presence of air in the catheter load. The latter was found to increase the potential for the embryo to be near the fundal area during the time limit for implantation. Based on the results of our simulations, we recommended performing ET in a patient-specific position in which the fundus will be the highest point above the horizon and that the load be delivered slowly, that is, not less than 10 s. We also recommended placing the tip of the catheter at the mid cavity to avoid ectopic pregnancy.

The pre-cycle blind mock embryo transfer is an inaccurate predictor of anticipated embryo transfer depth

PURPOSE

To assess if the uterine cavity depth measured by a blind pre-cycle mock transfer changes after gonadotropin stimulation.

METHODS

This is a retrospective cohort study at an academic IVF program involving 128 infertility patients. The main outcome measures were uterine cavity depth measured at the blind pre-stimulation mock transfer and the ultrasound-guided embryo transfer.

RESULTS

A >or= 1 cm increase in uterine cavity depth was found in 57.9% of the patients. The mean pre-cycle blind mock transfer uterine depth significantly differed from the mean uterine depth measured at embryo transfer. Based on the mock transfer, the anticipated embryo transfer depth was significantly less than the actual ultrasound-guided embryo transfer depth.

CONCLUSION

Uterine depth significantly differed between the blind pre-cycle mock transfer measurement and the ultrasound-guided embryo transfer measurement. The mock transfer may predict a difficult embryo transfer but it is an inaccurate predictor of the final embryo transfer depth.

In vitro simulations of embryo transfer in a laboratory model of the uterus

Embryo transfer (ET) is the final manual intervention during which the newly formed embryo is placed within the uterus by a transcervical catheter. The loading of the syringe-catheter complex with the transferred volume consists of the transfer media (which contains the embryos) separated by air spaces on both sides. The dynamics involved in injecting the syringe-catheter complex is not well understood nor has it been investigated to date. We developed an in vitro experimental setup for simulations of ET into a rigid transparent uterine model. The catheter was loaded in sequences of liquid and air as it is in the clinical setting. The transferred liquid was colored with a dye and its dispersion within the uterine cavity was recorded by a video camera. The results demonstrated, for the first time, the importance of having a gas phase in the catheter load. The resulting air bubbles within the uterus were carried upward towards the fundus by buoyant forces, thereby dragging behind them the transferred liquid which contained the embryos. This could be expected to substantially increase the probability for the embryos to be present near the fundal wall at the time window for implantation. There was also evidence of a dependency of the rate of injection upon the catheter load into the uterus: a low speed generated several air bubbles which led to more of the transferred liquid being carried towards the fundal end, thus possibly enhancing the potential for implantation.

Is what we clearly see really so obvious? Ultrasonography and transcervical embryo transfer—a review

OBJECTIVE

To critically review the role of ultrasound-guided embryo transfer (ET) and its influence on the outcome of in vitro fertilization (IVF).

DESIGN

Medline review of published manuscripts.

RESULT(S)

Studies evaluating the role of ultrasound-assisted ET have had mixed results, and although meta-analysis of prospective trials suggests an improvement in outcome, limitations in study design may overstate the effect of ultrasonography. Other ET techniques may eliminate the advantages provided by ultrasonography, limiting its benefit to specific clinical scenarios. However, because no trial has demonstrated an adverse effect and because cases that may benefit from its use often cannot be predicted reliably, the routine application of ultrasonography can be justified.

Advanced Combined Abdominal and Intrauterine Pregnancy: A Case Report

We present a case of simultaneous abdominal and intrauterine pregnancy following in vitro fertilization and embryo transfer diagnosed during the second trimester. The patient had a recent history of hysteroscopic metroplasty due to in utero exposition to diethylstilboestrol. The pregnancy was managed conservatively with a favorable outcome for the mother and both fetuses.

Ectopic pregnancy in a preexisting hydrosalpinx during a spontaneous pregnancy

OBJECTIVE

To discuss the possible role of abnormal embryo migration as a cause of ectopic pregnancy during IVF with hydrosalpinges.

DESIGN

Case report.

SETTING

University-based reproductive endocrinology and fertility clinic.

PATIENT(S)

A patient presenting with a tubal ectopic pregnancy after spontaneous conception in a preexisting hydrosalpinx.

INTERVENTION(S)

Laparoscopic salpingectomy.

MAIN OUTCOME MEASURE(S)

Ultrasound and operative findings.

RESULT(S)

Case demonstration of abnormal embryo migration into a surgically documented preexisting hydrosalpinx during a spontaneous conception.

CONCLUSION(S)

The mechanism of increased tubal ectopic pregnancy rates during IVF with hydrosalpinges remains unexplained. This case supports abnormal embryo migration due to the hydrosalpinx as a contributing factor.

Impact of hypnosis during embryo transfer on the outcome of in vitro fertilization-embryo transfer: a case-control study

OBJECTIVE

To investigate whether hypnosis during ET contributes to successful IVF/ET outcome.

DESIGN

Case-control clinical study.

SETTING

Academic Fertility and IVF Unit, Soroka Medical Center, Beer-Sheva, Israel.

PATIENT(S)

Infertile couples undergoing IVF.

INTERVENTION(S)

Ninety-eight IVF/ET cycles with hypnosis during the ET procedure were matched with 96 regular IVF/ET cycles.

MAIN OUTCOME MEASURES

Comparison of clinical pregnancy and implantation rates between the two groups.

RESULT(S)

We obtained 52 clinical pregnancies out of 98 cycles (53.1%) with an implantation rate of 28% among hypnosis IVF/ET cycles, and 29 out of 96 (30.2%) clinical pregnancies and an implantation rate of 14.4% in the control cycles. Our overall IVF program pregnancy rate for the same period was 32.1%. Logistic regression analysis was performed emphasizing the positive contribution of hypnosis to the IVF/ET conception rates.

CONCLUSION(S)

This study suggests that the use of hypnosis during ET may significantly improve the IVF/ET cycle outcome in terms of increased implantation and clinical pregnancy rates. Furthermore, it seems that the patients' attitude to the treatment was more favorable.

What can the clinician do to improve implantation?

Implantation is a complicated process that requires the orchestration of a series of events involving both the embryo and the endometrium. Even with the transfer of high quality embryos, implantation rates remain relatively low. The growing tendency towards transferring fewer embryos provides further incentives to improve implantation rates. In this article, the various clinical strategies employed to increase the chance of implantation are reviewed. Embryo transfer technique is a critical step in assisted reproductive technology cycles. Recent studies have shown significant improvements in clinical pregnancy rates resulting from careful embryo transfer technique, appropriate catheter type and placing for embryo transfer. Increasingly, adjuvant pharmaceutical therapies are also being applied with the aim of improving embryo implantation. However, the evidence for their efficacy and safety is limited. Recent evidence suggests that adoption of milder ovarian stimulation regimens may provide a more effective clinical approach to improving implantation, since beneficial effects have been shown for both endometrial receptivity and embryo quality.

Implantation sites after embryo transfer into the central area of the uterine cavity

A total of 63 pregnancies (47 singleton, 15 twin, 1 triplet) from intracytoplasmic sperm injection cycles were analysed. In all embryo transfers, the catheter was introduced into the endometrial cavity guided by abdominal ultrasound, with the catheter tip placed at the middle point of the endometrial cavity. Gestational sacs (GS) were located 21-24 days after transfer (gestational age=5 weeks) by two-dimensional and three-dimensional transvaginal ultrasound. The uterine cavity was divided into three parts: upper, middle and lower. Furthermore, the upper region was subdivided into right, middle and left areas, and the middle region was subdivided into right and left areas. The frequency of gestational sacs in each area was evaluated. In singleton pregnancies 66.0% (31/47) of the GS were detected in the upper region, 29.8% (14/47) in the middle region and 4.2% (2/47) in the lower region. In multiple pregnancies (twins and triplet) 45.5% (15/33) of the GS were detected in the upper region, 51.5% (17/33) in the middle region and 3.0% (1/33) in the lower region. In conclusion, the results demonstrate that when embryos are transferred to the central area of the uterine cavity there is an increase in implantation rate in the middle region compared with the rate expected in naturally conceived pregnancies (9-15%).

Embryo transfer: factors involved in optimizing the success

PURPOSE OF REVIEW

Embryo transfer is arguably the most critical step in assisted reproduction. The purpose of this article is to review the different aspects of the procedure in the light of recent evidence.

RECENT FINDINGS

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.

SUMMARY

Recent studies confirm the importance of the various aspects of embryo transfer. More randomized studies are needed to further evaluate them.

Factors affecting assisted reproductive technology (ART) pregnancy rates: a multivariate analysis

PURPOSE

To determine factors instrumental in achieving a clinical pregnancy in assisted reproductive technology (ART) patients.

METHODS

This study included 205 women undergoing their first ART cycle. Univariate and multivariate analyses were performed for patient demographics, in vitro production data, and factors associated with embryo transfer. Odds ratios (OR) were performed where appropriate.

RESULTS

Our analyses indicated that age (OR: 0.879), specific year in which the cycle was performed (OR: 2.959), and use of intracytoplasmic sperm injection (OR: 2.867) altered potential pregnancy rate. In addition, percent fertilization (OR: 1.028), number of embryos transferred (OR: 1.842), type of catheter used to transfer the embryos (OR: 0.377), presence of blood on the catheter (OR .414), and embryologist (OR: 2.338) also altered pregnancy rate.

CONCLUSIONS

Our data indicate patients' age, use of the Cook catheter, and presence of blood on the catheter reduce pregnancy rates. Performing ART in 1999, using ICSI, increasing fertilization rate, increasing number of embryos transferred (albeit less desirable when the chance of multiple gestation may occur), and transferring embryos via a particular embryologist, improve pregnancy rates.

Three dimensional/four dimensional ultrasound-guided embryo transfer using the maximal implantation potential point

OBJECTIVE

To evaluate the use of maximal implantation potential (MIP) point in conjunction with a 3D/4D ultrasound in order to facilitate embryo transfers and potentially improve pregnancy rate.

DESIGN

Retrospective, observational study.

SETTING

IVF Center.

PATIENT(S)

Between October 1, 2002, and August 27, 2004, 1,222 patients who underwent 3D/4D-ultrasound guided embryo transfers.

INTERVENTION(S)

Ultrasound-guided embryo transfer using a 3D/4D ultrasound machine and the MIP point.

MAIN OUTCOME MEASURE(S)

Procedure feasibility with improved visibility.

RESULT(S)

Embryo transfers were performed at the MIP point and the pregnancy rate was 36.66% (average patient age, 37.6 years). Physicians reported improved visualization and a greater accuracy in the placement of embryos within the uterine cavity.

CONCLUSION(S)

The MIP point can be immediately identified and individualized for each patient. Embryo transfers at the MIP were associated with good implantation and pregnancy rates.

Investigation and current management of recurrent IVF treatment failure in the UK

OBJECTIVE

To determine current practice in the management of recurrent in vitro fertilisation (IVF) treatment failure in licensed UK infertility centres.

DESIGN

National postal questionnaire study and literature review.

SETTING

University Hospital, Centre for Reproductive Medicine, Coventry, UK.

SAMPLE

Human Fertilisation and Embryology Authority licensed centres providing IVF/intracytoplasmic sperm injection (ICSI) in the UK (n = 79).

METHODS

A survey was designed that sought to determine how recurrent treatment failure was defined and which, if any, investigations were initiated. Furthermore, we asked which therapeutic options were subsequently recommended.

MAIN OUTCOME MEASURES

Definition of recurrent treatment failure. Investigations undertaken. Clinical or embryology changes recommended following recurrent treatment failure.

RESULTS

The response rate was 82%. The most common definition was three unsuccessful IVF cycles (range 2-6). Nineteen percent included frozen embryo replacements (FERs) in this figure. Anticardiolipin antibodies and lupus anticoagulant were the most frequent investigations suggested, followed by hysteroscopy and karyotype. A majority of centres would use a different treatment strategy in a subsequent cycle with blastocyst culture and assisted hatching being most popular.

CONCLUSIONS

The results of this survey suggest that there is considerable variation in the approach to investigation and management of recurrent IVF treatment failure in the UK, although in some areas (e.g. the definition) there was broad concordance. Not all of these approaches are evidence based.

Ultrasound-guided trial transfer may be beneficial in preparation for an IVF cycle

BACKGROUND

The objective of this study is to determine if ultrasound-guided trial transfer (UTT) in the office in preparation for an IVF cycle can be utilized as an alternative and/or adjunct to ultrasound-guided embryo transfer (UGET).

METHODS

Patients planning to undergo an IVF cycle at an academic centre were included. Each patient underwent an UTT in the office by the same practitioner. The difference in length (DL), if any, was measured from the perceived top of the uterine cavity (catheter tip) to the actual cavity apex as visualized by ultrasound.

RESULTS

Of the 64 patients enrolled, 19 patients (29.7%) had a measurable DL, of which 14 (21.9%) had a DL exists 0.5 cm, and nine (14.1%) had a DL exists 1.0 cm. Significant differences were noted between patients when comparing DL to previous pregnancy status and the total cavity depth (sounding depth + DL) (P < 0.05).

CONCLUSION

UTT in the office setting appears to be beneficial in preparation for an IVF cycle with embryo transfer.

Ultrasound-guided embryo transfer and the accuracy of trial embryo transfer

BACKGROUND

Studies have suggested that ultrasound-guided embryo transfer (UG-ET) may improve the outcome in IVF; however, several factors may account for the improvement in pregnancy rate. This study examines the use of ultrasound to determine the accuracy of trial transfer (TT) in preparation for ET.

METHODS

Sixty-seven consecutive patients prospectively underwent UG-ET over a 2 month period. Total cavity length by US was compared with the length noted by TT. A difference of > or = 1 cm was considered significant. All embryos were placed within 1-2 cm of the fundus by US.

RESULTS

Twenty patients (29.9%) had a difference of > or = 1 cm and 13 patients (19.4%) had a difference of < or = 1.5 cm. Patients with a difference of > or = 1 or > or = 1.5 cm had a significantly greater depth at transfer (P < 0.001) and uterine cavity length (P < 0.001) when compared with patients without a difference. Clinical pregnancy, implantation, delivery and overall miscarriage rates did not differ between patients with a difference of > or = 1 or > or = 1.5 cm versus no difference. There were no ectopic pregnancies.

CONCLUSIONS

Nineteen percent of patients had a discrepancy of > or = 1.5 cm and approximately 30% had a difference of > or = 1 cm from TT at UG-ET, suggesting a benefit to UG-ET. A large prospective randomized trial comparing UG-ET with blind transfer is required to assess further if UG-ET should be used in all cases of ET.

Recurrent implantation failure in assisted reproduction: how to counsel and manage. A. General considerations and treatment options that may benefit the couple

Recurrent implantation failure is a distressing phenomenon, both for the infertile couple and for the physician responsible for their treatment. Aetiology is often not clear and treatment options are vague. Particularly when transferred embryos are of good quality, recurrent implantation failure may be attributed to less than optimal embryo transfer technique, pathological lesions of the uterine cavity, the presence of hydrosalpinges, fibroids and endometriosis. Poor embryo quality, especially when repetitive, is a major impediment to successful implantation and cannot be corrected at the present time. Molecular abnormalities at the endometrial level and abnormal embryo-endometrium dialogue may be responsible for some cases of recurrent implantation failure. Furthermore, there may be over- or under-expressed genes that may be related to successful implantation. At the present time, the physician confronted with a couple presenting with recurrent implantation failure should discuss openly the potential causes of this phenomenon, with special emphasis on correctable causes, and offer remedies that are evidence based.

Implantation Failure in Assisted Reproduction Technology and a Critical Approach to Treatment

In this article, we review the literature and our personal experience regarding the many factors that appear to influence implantation rate. Oocyte quality, as determined by patient age and aneuploidies, probably plays a major role in RIF. However, a panoply of other factors have been brought under investigation, quite often with contradictory results and additional intriguing questions to be studied. Infections of the vagina, cervix, and endometrium, the role of mucus aspiration and washing of the cervix on transfer, the role of catheter guidance for a correct transfer and potion of embryos, the effect of mock transfer, and the role of hysteroscopy and its timing before transfer procedures are analyzed both as a review of the literature and as opinions and data from our experience. Many of these factors are interlaced and from the apparently simple issue of trauma, to infections and immune modulation of hatching and implantation, a biological continuum can easily be identified. The impact of abnormalities of the immune system and of homeostasis abnormalities is also covered in a brief overview of reported works and our experience. These latter areas probably constitute the common biological background of all other external factors that, however, the skilled must equip themselves for improving implantation success.

Increased implantation and pregnancy rates obtained by placing the tip of the transfer catheter in the central area of the endometrial cavity

The influence of endometrial cavity length (ECL) on implantation and pregnancy rates after 400 embryo transfers was studied prospectively in a population with the indication of IVF/intracytoplasmic sperm injection (ICSI). The tip of the transfer catheter was placed above or below the half point of the ECL in a randomized manner. Two analyses were performed: (i) absolute position (AP); embryo transfers were divided into three groups according to the distance between the end of the fundal endometrial surface and the catheter tip (DTC - distance tip catheter): AP1 (n = 212), 10-15 mm; AP2 (n = 158), 16-20 mm; and AP3 (n = 30), > or =21 mm. (ii) relative position (RP)--embryo transfers were divided into four groups according to their RP [RP = (DTC/ECL) x 100]: RP1 (n = 23), < or =40%; RP2 (n = 177), 41-50%; RP3 (n = 117), 51-60%; and RP4 (n = 83), > or =61%. Analysis based on relative distance revealed significantly higher implantation and pregnancy rates (P < 0.05) in more central areas of the ECL. However, analysis based on absolute position did not reveal any difference. In conclusion, the present results demonstrated that implantation and pregnancy rates are influenced by the site of embryo transfer, with better results being obtained when the catheter tip is positioned close to the middle area of the endometrial cavity. In this respect, previous analysis of the ECL is the fundamental step in establishing the ideal site for embryo transfers.