Intrauterine administration of human chorionic gonadotropin does not improve pregnancy and life birth rates independently of blastocyst quality: a randomised prospective study

In our study we investigated the impact of intrauterine hCG administration prior transfer in relation to blastocyst morphology in a large study population that includes birth outcome as primary outcome. In contrast to previous findings after cleavage stage embryo transfers, but in accordance with studies on blastocyst transfers, the present study did not show that intrauterine hCG application provides additional benefit in various settings [27]. In fact, neither intrauterine hCG injection on day three nor on day five had a beneficial effect on PR, DR, or IR. This was true in transfers with top blastocysts as well as in those with non-top blastocysts.

Several studies postulate that hCG is a key-player in the implantation process [8, 9, 14‐18]. As one of the first signalling molecules, hCG is already secreted by cleavage stage embryos. In blastocysts, hCG is then exclusively produced by the trophectoderm (TE) cells. Human chorionic gonadotropin isoforms and the released amount of hCG were found to be related to the developmental stage, but also to the morphological quality of the blastocyst and to the TE grading in particular [10, 28‐31]. In line with these findings, TE quality was suggested to be the most important predictor for implantation [32‐34]. It has recently been assumed that decidual cells select against embryos lacking fitness including those with insufficient hCG production [35]. Thus, our study aimed to investigate a possible positive effect of intrauterine hCG injection on implantation and clinical outcome in blastocyst transfers with regard to blastocyst morphology.

Our finding, that hCG did not improve clinical outcome neither in top-blastocyst transfers nor in non-top blastocyst transfer is in contradiction to some previous papers reporting positive results from cleavage stage embryo transfers (Table 5). Mansour and co-workers found in a randomised trial including 212 cycles that application of 500 IU hCG prior to transfer of cleavage stage embryos significantly improves pregnancy rates [19]. In a similar approach, Zarei and colleagues reported an increase in PR by intrauterine injection of 250 μg recombinant hCG (equivalent to 6,500 IU) prior to transfer on day three [20]. In both studies, the age of patients was substantially lower compared with our cohorts (Table 5). Advanced female age is the most limiting factor for IVF success. As some of the studies that have found a beneficial effect of hCG administration were done on younger patients, we investigated a possible benefit of hCG administration on patients with advanced maternal age. However, no benefit of hCG administration was found for different age groups 20 to 38 years or 38 to 43 years.

In line with our previous suggestion, that a beneficial effect of hCG application is dependent on the stage of the embryo(s) transferred, a recent study investigated blastocyst transfers in women >35 years [12]. No increase in cPR was observed in the hCG group. However, authors reported after further sub-grouping according to blastocyst quality, a higher PR with hCG injection when poor quality blastocysts were transferred [12]. This finding could not be observed in our study, which could be explained by the fact that in the cited study, the number of patients per group was substantially low. Our observations suggest that a putative decreased production of implantation supporting mediators in embryos with poor morphology cannot be overcome by intrauterine administration of hCG. On the contrary, a statistically significant negative effect of hCG administration prior to transfer on cPR and IR was observed in the poor morphology group. This might support the hypothesis that a well coordinated signalling is most crucial for a proper implantation and the enhancing of one signal might even worsen the situation. Thus, more trials addressing this issue might be needed. However, LBR was not statistically lower with hCG application (Table 4).

Moreover, in line with our results, the study of Rebolloso and colleagues did not observe any improvement in clinical outcome after administration of hCG [22]. This randomised study performed on a small cohort, including 38 patients who received 500 IU hCG and 83 patients in the control group. Transfers included both cleavage stage and blastocyst transfers. Interestingly, the authors reported a statistically significantly higher twin pregnancy rate after hCG injection (66 % vs. 8.3 % in hCG vs. control). This finding could not be confirmed in our data set. No differences in the two study cohorts were observed.

Consistent with our study, a recently published paper reported no impact of intrauterine hCG injection prior to blastocyst transfer [27]. This investigation included 300 fresh or frozen transfers. No statistically significant differences in IR or cPR between the hCG and control groups were observed. This was also true for a subgroup of patients receiving a transfer after comprehensive chromosome screening. These findings confirm our results, however, the cited study was discontinued before completion of the calculated sample size. Most important, the quality of blastocysts transferred was not further investigated, although it is well accepted that besides female age and the cause of infertility, blastocyst morphology is one of the most important parameters that determines whether or not implantation is successful [25, 36]. Data analysis in respect to the quality of transferred blastocysts is crucial, as embryo quality is probably an indicator of both: the hCG production and the probability of implantation [10, 11]. Our study clearly demonstrates that neither an intrauterine injection of hCG two days prior to ET nor an injection on the day of blastocyst transfer can overcome the reported reduced implantation chances of a poor quality blastocyst. This suggestion is in line with previous publication of Eftekhar et al. [37] and Ben-Meir et al. [38]. Both research groups observed that the subcutaneous administration of recombinant hCG in frozen-thawed ET cycles on the day of transfer does not have any advantages in terms of pregnancy and implantation rates. Further, in line with several previous reports, we did not observe an increase in miscarriages in the hCG groups when compared to controls. These results confirm previous findings [19‐22, 27]. In conclusion, this large prospective randomised study could not find any beneficial effect of intrauterine hCG injection (500 IU) in blastocyst transfers. This was true for top as well as for non-top blastocyst. The strengths of the present study are that it is an RCT with a high number of analysed subjects in two different set-ups, a unique stimulation scheme and the evaluation of the outcome in correlation to embryo quality. However, it has to be mentioned that the patient cohort receiving hCG injection on day 3 in our study was substantially smaller as compared to cohort B receiving hCG on day 5 prior to transfer and therefore this group did not reach the calculated power analysis. The main limitation is the restriction to fresh blastocyst transfers. The WOI is assumed to be altered by high dosages of exogenous hCG (as it is done during cycles of COH) [39]. Thus, a beneficial effect of intrauterine hCG administration in cryo-cycles cannot be excluded as the transfer of vitrified/thawed blastocysts is often suggested to be more physiologic. Furthermore, our results apply only to the patients clientele investigated in this study (autologous IVF cycles in patients ≤ 43 years). Additionally, as source and brand were found to be crucial for the mode of hCG action [18], we cannot exclude that other hCG concentrations or other hCG preparations might have different impacts.