Embryo transfer is the least successful step in assisted reproduction and 85% of the embryos replaced in the uterine cavity fail to implant. Various techniques have been suggested in order to optimize this apparently simple step, including performing a trial embryo transfer prior to the actual procedure, performing the transfer under ultrasound guidance, using soft catheters rather than the rigid ones, and asking the patients to rest in bed following the transfer.
DUMMY (TRIAL) EMBRYO TRANSFERS
It has been suggested that performing a trial embryo transfer in the cycle preceding the actual procedure could improve the outcome of assisted reproduction and this hypothesis has been confirmed by a RCT. In 1990, Mansour et al. conducted this trial and found that the clinical pregnancy and implantation rates increased significantly in those patients who had a trial
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embryo transfer compared to those who did not (22.8% versus13.1%, P < 0.05 and 7.2% versus4.2%, P < 0.05, respectively).22
ULTRASOUND-GUIDED EMBRYO TRANSFER
Many studies have reported that ultrasound-guided embryo transfer is associated with an increase in the clinical pregnancy and implantation rates. We have recently conducted a meta-analysis of RCTs and found that ultrasound-guided embryo transfer increased the clinical pregnancy rate significantly (odds ratio, 1.198; 95% CI, 1.018–1.410) as well as the implantation rate (odds ratio, 1.327; 95% CI, 1.168–1.507) and the on-going pregnancy rate (odds ratio, 1.456; 95% CI, 1136–1866).23
Ultrasound-guided embryo transfer is mainly used to confirm that the embryos are properly deposited in the uterine fundus and to follow the embryo- associated air bubble afterwards. We have also suggested that ultrasound can be used to measure the uterocervical angle (Fig. 1) and mould the embryo transfer catheter according to this angle. In a prospective controlled trial, we have found that this technique increased the clinical pregnancy (odds ratio, 1.57; 95% CI, 1.08–2.27) and implantation rates (odds ratio, 1.47; 95% CI, 1.10–1.96) significantly compared to the ‘clinical touch method’.24 The incidences of
difficult transfers (odds ratio, 0.25; 95% CI, 0.16–0.40) and blood (odds ratio, 0.71; 95% CI, 0.50–0.99) during transfers were also significantly reduced.
Fig. 1 Measuring the uterocervical angle prior to embryo transfer. (A) No angle; (B) small angle (< 30°); (C) moderate angle (30–60°); (D) large angle (> 60°). Reproduced with the kind permission of the Editor of Human Reproduction.
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SOFT CATHETERS VERSUS RIGID CATHETERS
Different types of embryo transfer catheters have been used in assisted reproduction with various claims of success. In particular, it has been suggested that soft catheters do not indent the uterine fundus and result in higher clinical pregnancy rates.25However, these claims have not yet been substantiated by other
RCTs. Larger RCTs are, therefore, necessary to determine the superiority or otherwise of any particular embryo transfer catheter.
SITE OF EMBRYO DEPOSITION
It has been suggested that depositing the embryos too near to the uterine fundus could risk injuring the endometrium and diminish the outcome of assisted reproduction and this hypothesis has recently been supported by a RCT. In this study, Coroleu et al. reported a significantly higher implantation rate when the embryos were deposited 2 cm below the uterine fundus compared to when deposited 1 cm below the fundus (P< 0.05).26
BED REST AFTER EMBRYO TRANSFER
Prolonged bed rest after embryo transfer does not improve the outcome of assisted reproduction. In 1997, Botta et al. conducted a RCT of 182 patients undergoing embryo transfer and found no statistically significant difference in clinical pregnancy rates between patients who rested in bed for 24 h after transfer compared to those who rested for 20 min only.27
OTHER FACTORS AFFECTING EMBRYO TRANSFER
It has also been suggested that cervical infection is detrimental to assisted reproduction. In an observational study, Egbase et al. cultured the tip of the embryo transfer catheter and found that the clinical pregnancy rate was significantly lower for patients with positive cultures compared to those with negative cultures.28When antibiotics were routinely administered to patients
with positive cultures, the clinical pregnancy and implantation rates improved significantly (from 17.8% to 41.3%, P< 0.01 and from 9.3% to 21.6%, P< 0.001, respectively). However, the value of routine administration of antibiotics has not been tested in a RCT.
On the contrary, RCTs have shown that waiting for 30 s before withdrawing the embryo transfer catheter and vigorous flushing of the cervical canal with culture medium before embryo transfer do not improve the clinical pregnancy rate.29
IMPLANTATION AND ENDOMETRIAL RECEPTIVITY
Medawar defined implantation as an immunological paradox whereby the semi-allograft human conceptus, immunologically foreign to the mother, evades immune rejection to penetrate and imbed in the semi-foreign endometrium. This fact is very much highlighted during assisted reproduction and various attempts have been made to improve endometrial receptivity in order to increase the clinical pregnancy and implantation rates. These include
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various regimens of luteal support, the use of corticosteroids, the removal of hydrosalpinges, diminishing uterine contractions as well as enhancing the endometrial blood flow (Table 2).
PROGESTERONE VERSUS HCG SUPPLEMENTATION
It has been suggested that the use of GnRHa down-regulation protocols could result in luteal phase insufficiency during assisted reproduction. In order to counteract this effect, luteal phase support has been used both by progesterone supplementation and/or HCG administration. In a meta-analysis of RCTs, Soliman et al. found that HCG administration improved the clinical pregnancy rate significantly in patients receiving GnRHa stimulation protocols (common odds ratio, 4.2; 95% CI, 1.9–9.1). However, this effect could not be evaluated in patients receiving other stimulation protocols due to the heterogeneity of the studies. On the contrary, they found that progesterone supplementation increased the clinical pregnancy rate significantly with all stimulation protocols (common odds ratio, 1.2; 95% CI, 1.0–1.7). When both luteal support methods were compared, HCG administration was superior to progesterone supplementation when GnRHa was used (common odds ratio, 2.0; 95% CI, 1.1–3.9), but not with other stimulation regimens.30
CORTICOSTEROIDS
Clinical studies have suggested that the administration of corticosteroids during IVF therapy might improve the clinical pregnancy rate.31 However,
different corticosteroid preparations were used in these studies and further RCTs using comparable preparations are necessary in order to confirm or refute these interesting observations.
REMOVAL OF HYDROSALPINGES
Various studies have shown that the presence of a hydrosalpinx has a detrimental effect on the outcome of assisted reproduction, apparently because the tubal fluid accumulates inside the uterine cavity. In 1999, Camus et al. conducted a meta-analysis of published studies and showed that the clinical pregnancy rate was significantly lower in patients with hydrosalpinges
Table 2 Odds ratio and 95% confidence intervals for the clinical pregnancy rate with various factors affecting implantation for patients treated with IVF
Stimulation protocol Odds ratio (95% CI)
HCG versus no HCG in GnRH agonist protocols30 4.2 (1.9–9.1)
Progesterone versus no progesterone in all protocols30 1.2 (1.0–1.7)
HCG versus progesterone in GnRH agonist protocols30 2.0 (1.1–3.9)
Hydrosalpinx versus no hydrosalpinx in IVF patients32 0.64 (0.56–0.74)
Removal of hydrosalpinx versus no removal34 1.75 (1.07–2.86)
Endometriosis versus tubal factor infertility35 0.81 (0.72–0.91)
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undergoing assisted reproductive measures compared to those with no hydrosalpinges (odds ratio, 0.64; 95% CI, 0.56–0.74). The implantation rate was also diminished (odds ratio, 0.63; 95% CI, 0.55–0.72) as was the delivery rate (odds ratio, 0.58; 95% CI, 0.49–0.69). Pregnancy loss was also significantly higher in patients with hydrosalpinges (odds ratio, 1.78; 95% CI, 1.31–2.48).32
Consequently, the removal of hydrosalpinges prior to assisted reproduction has been suggested as a measure to improve the outcome. A RCT conducted by Strandell et al. showed that the removal of the fallopian tubes in patients with bilateral hydrosalpinges increased their implantation, clinical pregnancy and delivery rates significantly (P < 0.05 in all cases).33 The removal of a
unilateral hydrosalpinx also increased the implantation and pregnancy rates, but this did not reach statistical significance, probably because the study lacked enough power.
More recently, a Cochrane Review conducted by Johnson et al. showed that laparoscopic salpingectomy significant increased the clinical pregnancy rate (odds ratio, 1.75; 95% CI, 1.07–2.86) as well as the live birth rate (odds ratio, 2.13; (95% CI, 1.24–3.65).34The implantation rate was also increased and the
ectopic pregnancy and miscarriage rates were diminished, but these changes did not reach statistical significance.
ENDOMETRIOSIS AND ASSISTED REPRODUCTION
A recent meta-analysis has shown that patients with endometriosis-associated infertility undergoing assisted reproduction have significantly lower pregnancy rates compared to patients with tubal factor infertility (odds ratio, 0.81; 95% CI, 0.72–0.91).35Moreover, patients with stages III and IV endometriosis have a lower
pregnancy rate compared to those with stages I and II (odds ratio, 0.60; 95% CI, 0.42–0.87). However, no evidence-based consensus has so far been reached on the best strategy to improve pregnancy rates in those patients.
FIBROMYOMATA AND ASSISTED REPRODUCTION
The effect of fibromyomata on the results of assisted reproduction is still a matter of controversy. While some RCTs have shown that the clinical pregnancy rates are diminished in these patients, other studies have not confirmed this effect particularly when the fibromyoma is not affecting the uterine cavity.36There is, therefore, a need for large RCTs in order to resolve the
issue and determine whether treatment of the fibromyomata prior to assisted reproduction is necessary.
OTHER FACTORS AFFECTING IMPLANTATION
Uterine contractions during embryo transfer have been blamed for diminishing the outcome of assisted reproduction. In an observational study, Fanchin et al. recorded uterine contraction during embryo transfer and found that fewer uterine contractions were associated with a higher clinical pregnancy rate. They also found that plasma progesterone concentrations and the frequency of uterine contractions were negatively correlated (r, –0.34; P< 0.001).37However, no RCT
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Sexual intercourse around the time of embryo transfer has also been suggested as a cause of low implantation rates after assisted reproduction. However, when a RCT was conducted by Tremellen et al., the clinical pregnancy rate was not affected by sexual intercourse and, contrary to expectations, the implantation rate was significantly increased for patients who had sexual intercourse around the time of embryo transfer.38
Endometrial echogenicity and vascularity were also studied for patients undergoing assisted reproduction. In a prospective study of 405 patients, Coulam et al. found that ultrasonic measurements of pulsatility index, resistance index, and the echogenic pattern were useful in predicting implantation after assisted reproduction, but these results were not confirmed in subsequent studies.39In an attempt to increase endometrial vascularity, Sher
and Fisch used sildenafil (Viagra) in 4 patients with previously failed IVF attempts and 3 of them conceived.40 However, to date, no RCTs have been
published to confirm this interesting observation. On the contrary, a RCT showed that the administration of low-dose aspirin did not improve implantation and pregnancy rates for patients undergoing ICSI.41
CONCLUSIONS
The multifaceted nature of assisted reproduction requires a meticulous evidence-based approach to the various steps involved in this treatment modality. With the ever-increasing numbers of patients in need of assisted reproduction, the clinical pregnancy rate can only be improved by relying on properly conducted RCTs.
Key points for clinical practice
• GnRHa down-regulation protocols are associated with higher clinical pregnancy rates compared to HMG-only protocols and the long protocols are superior to the short ones.
• GnRH antagonists protocols are not better than GnRHa protocols.
• Urinary FSH is better than HMG and recombinant FSH is better that urinary FSH.
• Natural cycle IVF is associated with lower pregnancy rates compared to controlled ovarian stimulation protocols, but is cheaper and does not produce hyperstimulation.
• Performing IVF and ICSI on sibling oocytes for patients with non- male factor infertility improves the fertilization rate and
prevents total fertilization failure.
• For the majority of patients, RCTs have not so far shown any clinical advantage in using co-cultures, group culture, in vitro maturation or assisted hatching. Embryo selection methods and blastocyst culture do not improve pregnancy rates but diminish the incidence of multiple pregnancies. (continued on next page)
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Key points for clinical practice (continued)
• RCTs have shown that ultrasound-guided embryo transfer, a trial transfer prior to the actual procedure and depositing the embryos 2 cm below the uterine fundus are associated with higher pregnancy rates. Bed rest and sexual intercourse do not affect the results.
• The value of using soft catheters, vigorous flushing of the cervical canal and the routine use of antibiotics has not been established.
• RCTs have established that the removal of any hydrosalpinx before assisted reproduction improves the clinical pregnancy rates. Endometriosis diminishes the clinical pregnancy rate and patients with polycystic ovaries have normal pregnancy rates but are liable to hyperstimulation.
• Progesterone supplementation increases the clinical pregnancy rates in all protocols, HCG increases the pregnancy rates in GnRHa protocols and HCG is superior to progesterone in GnRHa protocols. The value of using corticosteroids, uterine muscle relaxants, sildenafil and aspirin has not been established.
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