The use of fixed distance embryo transfer after IVF/ICSI equalizes the success rates among physicians

M.M.C. van de Pas1, S. Weima1, C.W.N. Looman2 and F.J.M. Broekmans1,3

1 Division for Reproductive Medicine, Department of Perinatology and Gynecology, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX Utrecht and 2 Department of Public Health, Faculty of Medicine and Health Sciences, Erasmus University Rotterdam, Dr. Molenwaterplein 50, 3015 GE Rotterdam, The Netherlands

3 To whom correspondence should be addressed. e-mail: F.Broekmans{at}azu.nl


    Abstract
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
BACKGROUND: It is suggested that the skill of the physician performing the embryo transfer may influence the outcome of the procedure. In this study we investigated the effects of a change in embryo transfer technique on the variability in success rates among physicians. METHODS: Retrospectively 4439 transfer cycles in which two different embryo transfer techniques were applied by seven physicians were studied. In the first 2210 cycles, transfers were performed using the ‘clinical touch’ method. In the following 2229 cycles, the so-called fixed distance technique was used. RESULTS: With the clinical touch method pregnancy rates differed greatly among providers, whereas after the introduction of the fixed distance technique these differences disappeared. Furthermore, the overall clinical pregnancy rate increased from 33.6 to 40.4% per transfer. Using smoothing spline curves we failed to detect a sudden rise in pregnancy rates at the time the transfer method was changed. CONCLUSIONS: The introduction of the fixed distance technique greatly reduced the variation in pregnancy rates among physicians. The overall increase in pregnancy rates after the introduction is likely to be related to the change in technique although definite proof is difficult. Both observations are suggested to be attributable to the atraumatic character of the fixed distance technique.

Key words: embryo transfer technique/IVF–embryo transfer/physician/pregnancy rate


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Embryo transfer is one of the critical steps in assisted reproduction procedures. Apart from embryo quality and the age of the patient, success rates after embryo transfer seem to be mostly dependent on factors that relate to the degree of trauma that is inflicted upon the endometrium and myometrium during the transfer procedure. Rigid catheters, blood contamination of the tip, increased myometrial contraction waves and higher degree of difficulty in entering the catheter into the uterine cavity all tend to reduce the probability of implantation of the embryo (Wisanto et al., 1989Go; Mansour et al., 1990Go; Gonen et al., 1991Go; Visser et al., 1993Go; Fanchin et al., 1998Go; Goudas et al., 1998Go; Lesny et al., 1998Go; Meriano et al., 2000Go). Also, pregnancy rates may vary greatly among individual providers (Karande et al., 1999Go; Hearns-Stokes et al., 2000Go). The technique used in the transfer procedure may be of importance by allowing for more or less traumatic procedures. The ‘clinical touch’ method was first described by Steptoe and Edwards and is a well-known technique for embryo transfer (Steptoe and Edwards, 1976Go). With this method the catheter is gently inserted into the cavity until it touches the fundal endometrium, is subsequently withdrawn for 0.5 cm, after which the embryos are expelled. Waterstone et al. suggested that the site of deposition of the embryos within the uterine cavity could have profound effects on success rates (Waterstone et al., 1991Go). Later this finding was also substantiated by Naaktgeboren (1998Go). By applying a technique in which the embryos are expelled at a fixed distance from the external os (6 cm), a remarkable decrease was observed in the variability in success rates among physicians: most physicians approximated the success rates of the best-performing physician (Naaktgeboren et al., 1997Go, 1998). A possible explanation for this effect may be that replacing embryos in the middle part of the uterus without touching the fundal endometrium allows for a less traumatic embryo transfer, especially for those physicians who have difficulties with approaching the fundal endometrium gently. As a result of these considerations, we decided to replace the clinical touch method by the fixed distance transfer technique in our IVF/ICSI programme and to retrospectively study the effect upon the variability in success rates among providers.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Patients and ovarian stimulation
The study was performed using the IVF database of a large tertiary referral centre for reproductive medicine. From the computerized patient charts, data were retrospectively collected on 4439 consecutive embryo transfer cycles. Clinical touch embryo transfers (n = 2210) were performed between January 8, 1996 and October 10, 1997. Fixed distance embryo transfers (n = 2229) were performed from October 10, 1997 onwards. Conventional IVF was performed as well as ICSI. No oocyte donation cycles or embryo transfers after cryopreservation were included. Only anonymized data were studied, so application for approval by the Board on Ethics in Human Research was not required.

The IVF treatment protocol was as follows: pituitary desensitization by daily s.c. leuprolide acetate injections (Lucrin 1 mg; Abbott, The Netherlands) in a long luteal suppression protocol was followed by ovarian stimulation with hMG (Pergonal; Serono Benelux BV, The Netherlands; or Humegon; Organon, The Netherlands) or human recombinant FSH (Metrodin HP; Serono Benelux BV). Ovarian stimulation was monitored by transvaginal ultrasonography and estradiol measurements. When the two largest follicles reached a size of 18 mm, hCG (Profasi, Serono; or Pregnyl, Organon) was administered, and transvaginal oocyte collection took place 34–36 h later. A maximum of two embryos was replaced in women aged <38 years. In older women three embryos were sometimes replaced. The luteal phase was supported by either hCG (Profasi; Serono) or progesterone (Progestan; Nourypharma BV, Oss, The Netherlands).

Embryo transfer procedure
Physicians were included in the study if they had performed >=100 embryo transfers with both the clinical touch method as well as with the fixed distance technique (>=100 with each method). In our dataset, seven out of eight providers met this criterion. The procedures for performing the embryo transfer were carefully written down in protocols, both for the practised clinical touch method, as well as for the newly applied fixed distance technique (>=100 with each method). The preparation for embryo transfer was the same for both techniques. Patients were placed in the lithotomy position and the cervix was exposed using a bivalve speculum. The cervix was cleaned with embryo culture medium. The embryos were loaded in the catheter tip with ~50 µl of media, fixed between air bubbles. All transfers were carried out using an Edwards Wallace Catheter (Simcare Ltd, UK). When there was difficulty passing the cervical canal or internal os with the loaded transfer catheter, it was withdrawn into the outer sheath, which was then used to facilitate the entrance into the cavity. If this made no progress a tenaculum was used to straighten the cervical canal. Ultimately, if passage could not be achieved, a switch was made to the TDT catheter (Prodimed, France). When the clinical touch method was used the catheter was advanced into the uterine cavity until its tip was felt touching the fundus. The tip was then withdrawn 0.5 cm and the embryos were expelled by advancing the plunger in the syringe, after which the catheter was gently withdrawn. When applying the fixed distance technique the catheter was advanced into the uterine cavity until 6 cm from the ostium externum. Then the embryos were expelled and the catheter was withdrawn. For both techniques the embryologist examined the catheter after the procedure to confirm that all embryos had been expelled before discharging the patient.

Variables
Primary variables, outcome variables and possible confounding variables were extracted from the database and listed in Table I. Pregnancy was defined as a positive urine pregnancy test, performed on day 14 after embryo transfer. Clinical pregnancy was defined as the presence of at least one gestational sac on ultrasonography, 2–3 weeks after a positive urine {beta}hCG test. Ectopic pregnancies were not counted as gestational sacs or clinical pregnancies. Implantation rate was defined as the number of gestational sacs on ultrasound, at a gestational age of 6–7 weeks, per 100 embryos replaced. The item ‘duration of infertility’ appeared not to be completed in 699 case records. As it is considered a relevant factor in the prediction of success in IVF–embryo transfer, this variable was not excluded from the analysis. The missing values were equally distributed among the two observation periods. When applying multivariate analysis this variable was omitted. Embryo quality was established according to the percentage of cytoplasmic fragmentation and the number of cells. Both items were given a score by the embryologist. For statistical comparison purposes and in order to quantify objectively the embryo quality, this score was composed as follows. Fragmentation <10% was given 5 points, 10–50% 4 points and >50% 3 points. Embryos having <4 cells, 4–7 cells, >=8 cells or a morula were given a score of 2, 3, 4 and 5 points respectively. The fragmentation and cell number score were multiplied for each transferred embryo, added up and divided by the number of embryos transferred. Hence, the mean embryo quality per patient (MEQ) was obtained. All analyses concerning MEQ score were done by dividing the dataset into groups of one specific transfer day (2, 3, 4 or 5) in order to compare embryo quality scores.


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Table I. Variables analysed
 
Data analysis
The main outcome variable was clinical pregnancy. SPSS 10.0 for Windows Statistical Package was used for statistical analysis. Continuous variables were compared by Student’s t-test if they were normally distributed. Otherwise, the Mann–Whitney U-test was used. Differences in proportions were analysed with the {chi}2-test. P < 0.05 was considered to indicate statistical significance. For the effect of several possible confounding factors on the outcome variable, we used univariate and multivariate logistic regression. Finally, we used smoothing spline curves to describe the change of pregnancy probability with time (Wegman and Wright, 1983Go). Thereby we aimed to assess whether a sudden change in pregnancy rates occurred near the time point at which the technique was altered in order to confirm a causal relation between the changed policy and the change in pregnancy rates.


    Results
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Before October 10, 1997 pregnancy rates differed greatly among physicians, whereas after the introduction of the new technique these differences clearly diminished (Table II). The differences among providers when using the clinical touch method were statistically significant ({chi}2-test, P = 0.0001). After the switch to the fixed distance technique no significant difference among the physicians could be observed. It is to be noted that two physicians greatly improved their rates (nos 1 and 2), two remained at their initial high level of performance (nos 4 and 7) and three showed non-significant improvement (nos 3, 5 and 6) (Table II). By splitting the whole study period into six periods of 210 days we wanted to ascertain that the disappearance of the heterogeneity between physicians occurred at the time of the switch in technique rather than as part of a gradual process. It is clear that before the switch consistently in all three periods the differences among providers were statistically significant, whereas after the switch a significant difference was consistently absent (Table III). Using multivariate analysis the physician replacing the embryos appeared to be an independent predictor of success when the clinical touch method was used (P = 0.0001), whereas after the switch in technique this factor was no longer significant. With the change in technique the overall clinical pregnancy rate increased from 33.6 to 40.4% per transfer ({chi}2-test, P = 0.0001). Also, the implantation rate and twin rate significantly increased after the switch in transfer technique (Table II).


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Table II. Number of embryo transfers and clinical pregnancy rates (CPR) per embryo transfer for the individual provider, overall clinical pregnancy per embryo transfer, implantation (IR) and twinning (TR) rates, split by technique of embryo transfer
 

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Table III. Clinical pregnancy rates for all physicians divided according to period
 
To explain both the increased homogeneity in success rates among providers as well as the increased clinical pregnancy rates independently of the change in embryo transfer technique, we analysed which factors were most predictive for the occurrence of clinical pregnancy by using univariate logistic regression on the whole of the study period (Table IV). The number of embryos transferred was one of the most predictive variables, as can be expected. When transferring one additional embryo, the pregnancy rate will show a 65% increase. Using multivariate step-wise logistic regression on all variables, except duration of infertility and MEQ score, we identified the following independent prognostic variables of the probability of clinical pregnancy: age, number of transferred embryos, previous pregnancies after IVF/ICSI, treatment cycle number and number of oocytes recovered (Table IV). MEQ score was analysed in separate logistic regression analyses for day 2, 3, 4 or 5 transfers. In every one of the analyses, MEQ score was selected as independent predictive factor for clinical pregnancy rate (data not shown).


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Table IV. Logistic regression analysis with odds ratios (OR) for the prediction of clinical pregnancy
 
The six variables identified as independently prognostic for the occurrence of clinical pregnancy were then analysed for statistical differences before and after the switch in embryo transfer technique (Table V). None of them appeared to differ significantly, except for the mean embryo quality score on day 2 and 3. These differences in MEQ scores have only limited clinical significance, as the absolute difference in means is just 0.4 and 0.5 points respectively. When transferring an embryo on day 3 with one unit fragmentation score higher, the mean embryo quality score is already increased with 1.0 points if three embryos are transferred. When transferring two embryos or one embryo this score will increase even more (1.3 and 3.0 MEQ score points respectively). A mean change in MEQ score per patient of 0.5 point would change the probability of clinical pregnancy after the transfer by 7.4% (deduced from the logistic regression analysis). With an overall clinical pregnancy rate per transfer of 33.6% before the change in transfer technique, the observed increase in MEQ score would allow for an increase to 36.1% after the change, if day 3 transfers are considered. Therefore, from this analysis on the influence of mean embryo quality, no full explanation for the change in overall pregnancy rates could be deduced.


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Table V. Comparison of clinical data for predictive variables of the clinical touch and the fixed distance embryo transfer methods, tested with the Mann–Whitney U-test (except for age which is tested with the Student’s t-test)
 
To further address the question whether the increase in overall pregnancy rate per transfer could be attributed to the use of the fixed distance technique, we applied the statistical technique of the smoothing spline curve of pregnancy probability. This probability curve would enable us to assess whether the change in embryo transfer technique caused a sudden rise in rates at the time the transfer technique was changed. In Figure 1 it is shown that there is initially a marked fluctuation in pregnancy probability after embryo transfer. At the time of method change there already is an upward trend, which continues until reaching a rather high plateau. At the end of the observation period a short, sudden, decline in probabilities is found. No clear, sudden, rise in probability is observed around the date of October 10. The lack of a ‘fraction’ moment in the spline curve implies that solid statistical evidence for a relation between change of technique and increase in pregnancy rates could not be obtained.



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Figure 1. Smoothing spline curves of predictive probabilities of clinical pregnancy for the two periods: before (black) and after the switch in technique (grey).

 

    Discussion
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
With the use of the fixed distance technique of embryo transfer, a remarkable homogeneity was achieved in the success rates among physicians. The outcome of the embryo transfer in terms of clinical pregnancy rate differed greatly between physicians when the clinical touch method was applied. After the introduction of the fixed distance technique the difference among providers with regard to pregnancy rates appeared to be only minimal. Conditions believed to affect success rates after embryo transfer, apart from embryo quality per se, are the type of catheter used, the presence of blood on the catheter after completion of the transfer and the avoidance of touching the uterine fundus. All these factors seem to have in common that they express the degree of atraumaticity of the transfer (Kovacs, 1999Go; Salha et al., 2001Go). The use of a soft catheter results in an increase in clinical pregnancy rates compared with rigid catheters (Wood et al., 2000Go; Choe et al., 2001Go; McDonald and Norman, 2002Go; Van Weering et al., 2002Go). In several studies it has been suggested that techniques that prevent bleeding at the time of embryo transfer have a beneficial effect on the success rates (Visser et al., 1993Go; Goudas et al., 1998Go). Unfortunately, we did not have reliable data to include the proportion of difficult transfers or transfers with blood at the catheter tip in the confounder analysis.

Ultrasound-guided embryo transfer is designed to assure the correct position of the catheter in the uterine cavity, avoid touching the fundal area and thereby prevent the occurrence of bleeding and uterine contractions (Fanchin et al., 1998Go; Lesny et al., 1998Go). Coroleu et al. (2002Go) demonstrated that embryo transfer under ultrasound guidance compared with the clinical touch method improved pregnancy rates and these findings were confirmed by others (Lindheim et al., 1999Go; Wood et al., 2000Go; Kojima et al., 2001Go; Anderson et al., 2002Go). The critical role of chemical (blood) or mechanical (uterine contractions) trauma in the success rates after embryo transfer provides an explanation for the effect of the transfer technique on the differences among physicians with regard to pregnancy rates, as found in the present study. In using the clinical touch method, differences in the skill of the physician to very gently approach the fundus, never miss the touch moment and thereby creating a minimally traumatic transfer may account for the differences in pregnancy rates. In contrast, the fixed distance technique makes it possible for any provider to replace the embryos atraumatically, as the fundus need not be touched for assessing the correct position of the catheter tip in the cavity at the time of expelling the embryos.

The change in embryo transfer technique was paralleled by a significant increase in the overall pregnancy rates in our centre. As all physicians improved their pregnancy rates towards those of their best-performing collegues, it is tempting to attribute the rise in overall pregnancy rates to the change in technique. Obviously, the change in pregnancy rates after the switch may have been caused by many known or unknown factors. We analysed factors that are well known to play a role in the outcome of pregnancy after embryo transfer (Roseboom et al., 1995Go) and that were selected from our own data by multivariate logistic regression. We could not find clear differences in these factors before and after the switch in technique, apart from the factor embryo quality that may have contributed partly to the observed difference. Moreover, we tried to causally link the change in embryo transfer technique to the change in pregnancy rates by showing that around the time of the switch a sudden increase occurred in the pregnancy rates when using smoothing spline curves. However, we did not succeed in finding a fraction moment in the spline curve around the day of change in transfer technique. It is certainly unlikely that introducing a new technique on a given day will alter pregnancy rates immediately. Before the new technique started to be applied, a great deal of attention was paid to the role of the transfer technique in success rates. Physicians had to get used to the new technique or may have changed attitude beforehand. For these reasons the increase in pregnancy rates may show a gradual upward tendency instead of a sudden rise and may not be detectable by the technique of splining. Furthermore, another explanation may be that pregnancy rates always fluctuate with time in any centre for reproductive medicine. The fixed distance technique was introduced in a period where the trend was already upwards and this may certainly hamper the analysis of the relationship between the method and pregnancy rates. Also there may have been unknown factors which have changed between the two study periods which have not been revealed by the stepwise logistic regression analysis. Finally, proof for an overall effect on pregnancy rates can only be obtained from a prospective back-to-back comparison between the clinical touch and the fixed distance methods. To our knowledge such a study has not been performed.

With the retrospective nature of the study these arguments prevent us from drawing firm conclusions as to the question of whether overall pregnancy rates can be expected to go up if this technique is introduced in any centre for reproductive medicine.

The fixed distance technique of embryo transfer provides a simple and physician-proof method for embryo replacement. When using the fixed distance technique, embryos are being transferred at 6 cm from the external os irrespective of the individual length of the uterus. As no clear answer exists to the question in what part of the cavity the embryos need to be expelled from the catheter to obtain the best pregnancy rates, further study is needed at this point. Recently, Coroleu et al. (2002Go), using ultrasound controlled embryo transfer, suggested that replacement further away from the fundus will improve implantation rates. This means that assessing the sounding length of the uterus before applying the fixed distance method and using a distance ~1.5–2 cm away from the fundus may optimize the performance of the fixed distance transfer procedure. Egbase et al. (2000Go) studied the sounding length of the uterus in IVF patients by measuring the distance from the external cervical os to the fundus during a mock transfer procedure. They found that 16% of their patients appeared to have a uterine cavity length of <7 cm, meaning that in those patients a fixed distance technique at 6 cm would lead to replacing of the embryos at too short a distance from the fundus or even to touching of the fundal endometrium. In 10% of cases the cavity length was >9 cm and this may lead to replacement at a point too far away from the fundal area. To ensure that the embryos are expelled at the right distance from the uterine fundus, the sounding length of the uterus should be measured before the transfer. Pre-transfer assessment of the uterine cavity length may well be possible by using transvaginal ultrasound, although studies confirming the accuracy of this method are lacking. Mock transfer procedures will provide essential information on the depth of replacement but may be considered as a disproportionate burden for the patient as well as the doctor (Sharif et al., 1995Go). The use of ultrasound-guided embryo transfer (Kan et al., 1999Go; Lindheim et al., 1999Go; Coroleu et al., 2000Go; 2002; Wood et al., 2000Go; Tang et al., 2001Go; Karande et al., 2002Go) offers another approach where the transfer depth can instantaneously be assessed according to the ultrasound image of the uterus. However, in transvaginal ultrasound-guided embryo transfer it may be quite difficult to simultaneously place the ultrasound probe, the speculum and the catheter. If abdominal scanning is used, the bladder needs to be filled, and the catheter may not always be easily visualized on the scan, while the need for extra staff to handle the ultrasound probe is obvious (Hurley et al., 1991Go; Kovacs, 1999Go). In conclusion, our study confirms that the large differences between physicians performing embryo transfers using the clinical touch method can be smoothed away by the application of the fixed distance technique. Whether the change in technique can be held responsible for an overall improvement of success rates remains difficult to prove. Future studies should be directed towards individualizing the depth of replacement and comparison with the ultrasound-guided transfer techniques.


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
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Submitted on November 21, 2002; accepted on January 7, 2003.