STUDY QUESTION

Do both ulipristal acetate (UPA) and mifepristone inhibit embryo-endometrial attachment at concentrations corresponding to the emergency contraception (EC) dose?

SUMMARY ANSWER

Both UPA and mifepristone at concentrations corresponding to the EC dose do not have an inhibitory effect on embryo implantation, although mifepristone at a higher concentration appeared to have such an effect.

WHAT IS KNOWN ALREADY

Levonorgestrel is commonly used for EC, but it only acts through inhibition of ovulation. UPA and mifepristone have higher efficacy as EC compared to levonorgestrel; while there is some suggestion that mifepristone may interfere with implantation, whether UPA has post-ovulatory action in inhibiting implantation is yet to be confirmed.

STUDY DESIGN, SIZE, DURATION: An in vitro experimental study using trophoblastic spheroids made from JAr cell line as the embryo surrogate, and the Ishikawa cell line and primary human endometrial cells cultured to monolayer as the endometrial surrogate. The primary endometrial cells were collected from nine volunteer women in the mid-luteal phase with consent.

PARTICIPANTS/MATERIALS, SETTING, METHODS: The study was conducted in a university gynaecology unit. The JAr and Ishikawa cell lines (or primary endometrial cells) were treated with graded concentrations of UPA (0, 0.04, 0.4 and 4 μM) or mifepristone (0, 0.1, 1 and 10 μM) for 24 h. Embryo-endometrial attachment was studied using an in vitro JAr spheroid-endometrial co-culture model. Expressions of progesterone receptor, β-catenin and glycogen synthase kinase 3 β (GSK-3β) were studied with real-time RT-PCR and Western blotting, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

In the Ishikawa experiments, there was no significant difference in the JAr spheroid attachment rate after treatment with UPA at 0 (93.0%), 0.04 (93.6%), 0.4 (93.4%) and 4 (91.4%) μM concentrations (P > 0.05); the attachment rate was reduced after treatment with mifepristone only at 10 μM (79.8%, P < 0.0001) but not at 0.1 (92.1%) or 1.0 (95.2%) μM concentrations. In the primary endometrial cell experiments, again no significant difference was observed in the JAr spheroid attachment rate after treatment with UPA 4 μM (42.6%) compared to control (46.5%, P > 0.05). Both UPA and mifepristone could significantly up-regulate progesterone receptor expression. There was no significant alteration in expression of β-catenin and GSK-3β after treatment with UPA 4 μM or mifepristone 10 μM (P > 0.05).

LIMITATIONS, REASONS FOR CAUTION: The co-culture model is only a surrogate which may not fully represent the complicated process of embryo implantation in vivo, although there is no existing perfect model for studying implantation in vitro which fully resembles the latter.

WIDER IMPLICATIONS OF THE FINDINGS

The lack of inhibitory effect on embryo implantation by UPA and possibly mifepristone at concentrations corresponding to the EC dose is an important information for contraceptive counseling.

STUDY FUNDING/COMPETING INTEREST(S): We had free supply of the UPA compound used in this study from Laboratoire HRA Pharma. This work was supported by a Seed Fund from the Centre of Reproduction, Development and Growth, Faculty of Medicine, The University of Hong Kong, Hong Kong.