Influence of position and length of uterus on implantation and clinical pregnancy rates in IVF and embryo transfer treatment cycles

P.E. Egbase,, M. Al-Sharhan and J.G. Grudzinskas,

1 IVF Centre, Maternity Hospital, Kuwait and 2 Department of Obstetrics & Gynaecology, St Bartholomew's & The Royal London School of Medicine & Dentistry, Royal London Hospital, London E1 1BB, UK


    Abstract
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
In a prospective study of 807 consecutive women shown to have an apparently normal uterus after hysterosalpingography, hysteroscopy or pelvic ultrasonography prior to IVF or intracytoplasmic sperm injection (ICSI) and embryo transfer, the position and length of the uterine cavity was measured routinely at a pre-treatment mock transfer procedure. The apparent length of the uterine cavity was <7 cm in 128 women (group 1), 7–9 cm in 594 women (group 2) and >9 cm in 85 women (group 3). The uterus was noted to be retroverted in 38.2% (308) women. The embryo transfer catheter was advanced to 5 mm from the uterine fundus based on the previously determined cavity length in all the embryo transfer procedures at 48 h after oocyte collection. Implantation and clinical pregnancy rates were not significantly different with respect to position of the uterus, difficulties encountered in passage of the catheter, mean age of the women, aetiology or duration of infertility or embryology events. An apparently greater cavity length was seen in older and/or parous women, but the difference was not statistically significant. Although the highest implantation and clinical pregnancy rates were seen in women with a cavity length of 7–9 cm (group 2) the differences were not statistically significant: group 1, 18.9 and 36.7%; group 2, 21.0 and 46.5%; and group 3, 17.3 and 32.9% respectively. The incidence of ectopic pregnancy per reported clinical pregnancy was highest in group 1 women, being 14.9% (7/47) in comparison with group 2 (1.8%, 5/276) and group 3 (0%, 0/27) (P < 0.0005), suggesting that the size of the uterus is a critical factor in the aetiology of ectopic pregnancy in IVF/ICSI–embryo transfer.

Key words: ectopic/embryo transfer/implantation/pregnancy/uterus


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The embryo transfer procedure is the last decisive step of IVF and embryo transfer but the practice of transcervical embryo transfer has changed little in the past 20 years. Typically, a syringe is attached to a fine plastic catheter into the tip of which is drawn 10–25 µl of culture medium containing the embryos usually flanked by air bubbles (Steptoe and Edwards, 1978Go; Englert et al., 1986Go; Vaught et al., 1987Go). The loaded catheter is gently and slowly manipulated through the cervical canal and advanced a variable distance within the uterine cavity before pressure on the syringe plunger expels the embryos. The embryos' fate in the uterine cavity is beyond our control and not much is known about the location of the embryos after transfer or how much they move before implantation occurs except for a few reports on the fate of radio-opaque dye, air bubbles, methylene blue or Echovist (Schering Health Care, Burgess Hill, Sussex, UK) that have been used to mimic embryos in a mock transfer procedure (Knutzen et al., 1992Go; Mansour et al., 1994Go; Woolcott and Stanger, 1997Go; Lesny et al., 1998Go). Controversies abound in the literature on the optimal site within the uterine cavity to deposit the embryos, being variously described as just above the internal cervical os in the lower uterine cavity (Waterstone et al., 1991Go), mid-cavity (Woolcott and Stanger, 1997Go; Lesny et al., 1998Go) or 5 mm from the fundus (Knutzen et al., 1992Go; Agarwal et al., 1994Go). This study examines the influence of the position or length of the uterus from the external cervical os to the fundus on the implantation and clinical pregnancy rates when embryos are routinely deposited 5 mm from the fundus in an otherwise classical transcervical embryo transfer procedure.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
This was a prospective study of 807 consecutive infertile women reaching IVF/intracytoplasmic sperm injection (ICSI)–embryo transfer in the period of May 1997 to August, 1999 at the IVF Centre, Maternity Hospital, Kuwait who were shown to have a normal uterus on hysterosalpingography, hysteroscopy and/or pelvic ultrasonography. All patients received gonadotrophin-releasing hormone (GnRH) agonist analogue (buserelin; Aventis Pharma, Frankfurt, Germany) administered in the mid-luteal phase to achieve pituitary desensitization. After 10–14 days of onset of pituitary desensitiza- tion and when the serum oestradiol concentration had dropped to <150 pmol/l, pre-stimulation ultrasonography was performed on all patients by one of the authors (P.E.). The patient was placed in the lithotomy position and, with an empty bladder, transvaginal pelvic ultrasonography was performed to determine position of the uterus which was classified as anteverted or retroverted. Subsequently, a bivalve vaginal speculum was introduced and the cervix exposed. An intrauterine catheter with 1 cm graduations on the outer sheath and fitted with an inner flexible steel stylet (Casmed, Surrey, UK) was gently introduced through the external os to reach the uterine fundus. The length of the uterine cavity from the external cervical os to the fundus was measured. The women were subsequently divided into three groups according to uterine cavity length for the purpose of this study: group 1 (n = 128), <7 cm; group 2 (n = 594), 7–9 cm; group 3 (n = 85), >9 cm.

The details of the ovarian stimulation regimen have been previously described (Egbase et al., 1996Go). Transvaginal oocyte retrieval was performed 35–36 h after the human chorionic gonadotrophin (HCG) trigger (10 000 IU) injection. Intra-operative antibiotics (Metronidazole 1 g i.v. and cephatriaxone 2 g i.v.) were administered during oocyte retrieval (Egbase et al., 1999Go). The oocytes were subjected to conventional IVF or ICSI according to the cause of infertility (Egbase et al., 1997Go). Transcervical intrauterine transfer of up to three embryos in 15–25 µl of culture medium (IVF-20; IVF Science Scandinavia, Vitrolife Productions AB, Gothenburg, Sweden) flanked with air bubbles was performed in all patients ~48 h after oocyte retrieval using an Edwards–Wallace embryo replacement catheter (SimCare, Lancing, W Sussex, UK). This catheter is marked with 1 cm graduations allowing the clinician (P.E.) to advance it to 5 mm from the uterine fundus based on the previously determined length of the uterine cavity from the external cervical os. Thus, the embryos were routinely deposited 5 mm from the fundus irrespective of the length of the uterine cavity. When there was difficulty in passing the catheter, the cervix was held with a tenaculum and a Wallace malleable stylet with an outer sheath (Simcare, Lansing, West Sussex, UK) was carefully introduced through the cervical canal. Once it passed the internal cervical os, the stylet was removed and the inner Teflon of the Edwards–Wallace embryo replacement catheter loaded with embryos was introduced through the outer sheath already in place in the cervical canal. Again, the catheter was advanced to 5 mm from the uterine fundus before depositing the embryos. All embryo transfer procedures were performed in the modified lithotomy position and patients with anteverted uteri were routinely required to have a half-full bladder prior to the embryo transfer (Lewin et al., 1997Go).

Implantation and clinical pregnancy rates were both determined by the presence of a regular gestation sac with embryonic/fetal heart activity at pelvic ultrasonography performed 4–5 weeks after embryo transfer, while the ectopic pregnancy rate was calculated per reported pregnancies, i.e. clinical and ectopic pregnancies.

Statistical analysis
Relevant differences observed between groups were subjected to the {chi}2-test to determine their statistical significance (P < 0.0005).


    Results
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
In 308 (38.2%) women, the uterus was retroverted. The implantation and clinical pregnancy rates were marginally higher in the women with anteverted uteri (21.5 versus 18.4% and 44.1 versus 38% respectively), but the differences were not statistically significant (Table IGo). The incidence of difficult transfers was similar in relation to the uterine position (2.8 and 2.6% in anteverted and retroverted uteri respectively) and length of the uteri (2.5, 3.1 and 2.8% in groups 1, 2 and 3 respectively). There were no significant differences in the mean age, indication and duration of infertility and embryology events (fertilization and cleavage rates) and mean number of embryos transferred per woman in relation to the position of the uteri (Table IGo). Increasing length of the uterine cavity appeared to be associated with greater mean maternal age and parity (Table IIGo), but none of the differences was statistically significant. The implantation and clinical pregnancy rates appeared to be higher in women with a uterine cavity length of 7–9 cm, i.e. normal size uteri (groups 1, 2 and 3 being 18.9, 21.0 and 17.3% and 36.7, 46.5 and 32.9% respectively) but the differences were not statistically significant.


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Table I. Age, duration and cause of infertility, embryology events, implantation and clinical pregnancy rates in relation to the position of the uterus
 

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Table II. Age, parity, duration and cause of infertility, embryology events, implantation, clinical pregnancy and ectopic pregnancy rates in relation to the length of the uterus
 
The incidence of ectopic pregnancy per reported pregnancy was 14.9% (7/47) in group 1, 1.8% (5/276) in group 2 and 0/27 in group 3 patients, and this difference was statistically significant (P < 0.0005) when group 1 was compared with group 2. The differences in groups 1 and 3 were not subjected to statistical analysis because of the small numbers. There were no other significant differences between the three groups with respect to the mean age, indication and duration of infertility, embryology events (fertilization and cleavage rates) and mean number of embryos transferred per woman (Table IIGo).


    Discussion
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
There remains a compelling need in the practice of assisted reproductive technology to evaluate any variables that may influence the implantation rates following IVF/ICSI–embryo transfer. Embryo implantation has remained discordantly low and at variance with the high fertilization and cleavage rates that have marked advances in assisted reproductive technology (Edwards and Beard, 1999Go). There are no reports that the position or the length of uterus from the external os to the fundus has any apparent influence on the implantation and clinical pregnancy rates in spontaneous conceptions. It is logical to assume that following fertilization in vivo, the blastocyst reaching the uterine cavity by the fourth or fifth day would attempt to implant at a site suitable for successful clinical pregnancy. Amongst many other factors, implantation at sub-optimum site within the uterus could account for some of the pre-clinical miscarriages in spontaneous conceptions.

It is not clear if there is such an optimum site within the uterine cavity and this probably explains why clinicians deposit embryos following IVF at various sites within the uterine cavity. Waterstone et al. (1991) suggested that deposition of embryos in the lower uterine cavity resulted in a much better pregnancy rate while Yovich et al. (1985) and Nazari et al. (1993) associated a higher incidence of ectopic pregnancies following IVF–embryo transfer with placement of embryos close to the uterine fundus. On the contrary, Knutzen et al. (1992), using a radio-opaque dye bolus to mimic the fate of embryos in mock embryo transfer, showed that 68% of the bolus was retained in position when placed at 5 mm to the fundus. In a recent survey (Kovacs, 1999Go), clinicians performing transcervical embryo transfer rated not touching the fundus as the third most important factor in the technique of embryo transfer but there was no mention of the optimum site within the uterine cavity at which the clinicians would routinely prefer to deposit the embryos. Wood et al. (2000) amongst others suggest that ultrasound-aided embryo transfer was superior to a blind attempt to put the embryo near the fundus.

In this study and as is the routine practice in our unit, the embryos are routinely placed ~5 mm from the fundus, a distance determined from the previous measurement of the uterine cavity at the mock embryo transfer. The length of the normal uterine cavity, including the cervical canal, is considered to be not <7 cm and is usually 7.5–8 cm (Tindall, 1987Go). The long protocol administration of GnRH agonist for 10–14 days is unlikely significantly to influence the length of the uterine cavity. The implantation and clinical pregnancy rates were similar whether the uterine cavity was small in size (<7 cm), normal size (7–9 cm) or large (>9 cm) when the embryos were routinely placed 5 mm from the fundus. It is not known if varying the distance from the fundus in relation to the length of the uterine cavity would have an impact, although there is evidence that pinopodes that characterize endometrial receptivity are probably present 2 cm down from the fundus (Nikas et al., 1995Go).

The incidence of ectopic pregnancy per reported pregnancy was 14.9% (7/47) when the uterine cavity was small, 1.8% (5/276) when the uterine cavity was normal size and 0/28 in patients with large uterine cavities. The statistically significant higher ectopic pregnancy rate seen in patients with small uterine cavity (external cervical os to the uterine fundus <7 cm) compared with patients with normal uterine cavity lengths suggests that ectopic pregnancy may be related to the size of the uterine cavity but is not necessarily exclusive of the clinical technique of placing the embryos 5 mm from the fundus in IVF–embryo transfer as previously suggested (Yovich et al., 1985Go; Nazari et al., 1993Go). This is the first report in the medical literature implicating the size of the uterine cavity in the aetiology of ectopic pregnancy. The incidence of tubal infertility was similar in the three groups of patients (Table IIGo) and amongst the patients with ectopic pregnancy in group 1 (2/7) and group 2 (1/5). In addition to tubal factor infertility (Strandell et al., 1999Go), the fundal distance between the tubal ostia, likely to be related to the uterine size, could be a critical factor in the aetiology of ectopic pregnancies in IVF/ICSI–embryo transfer. Also it is unclear if the intensity of waves of uterine contractions at the time of embryo transfer (Fanchin et al., 1998Go) is related to size of the uterus or if such uterine activity is more likely to predispose to tubal displacement of embryos in patients with small uteri. In a series of mock embryo transfers, Knutzen et al. (1992) demonstrated complete, partial or temporary displacement of dye used to mimic embryos to the Fallopian tubes in 38.2% of cases associated with uterine contraction as the mock embryo transfer catheter was removed from the uterus. Although difficult embryo transfer probably increases the odds ratio for ectopic pregnancy in IVF–embryo transfer (Lesny et al., 1999Go), the incidence of difficult embryo transfer in this study was similar in relation to both the length and position of the uteri. Further studies are required to examine the role of the size of the uterine cavity and any related mechanisms in the aetiology of ectopic pregnancies in IVF/ICSI–embryo transfer and possibly in spontaneous conception. Patients can be reassured that the position of the uterus (anterveted or retroverted) does not adversely affect implantation or clinical pregnancy rates, confirming the earlier findings in a smaller group of patients (Agarwal et al., 1994Go).


    Notes
 
3 To whom correspondence should be addressed at: Department of Obstetrics & Gynaecology, St Bartholomew's & The Royal London School of Medicine & Dentistry, Royal London Hospital, London, E1 1BB, UK. E-mail: j.g.grudzinskas{at}mds.qmw.ac.uk Back


    References
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
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Submitted on February 7, 2000; accepted on June 13, 2000.