Vaginal bioelectrical impedance determines uterine receptivity in mice.

Study Question: Can vaginal bioelectrical impedance (VZ) electrophysiologically determine alterations of the endometrium in preparation for implantation?

Summary Answer: VZ can electrophysiologically detect the sulfation and sialylation changes in the uterine glycocalyx in preparation for implantation.

What Is Known Already: Uterine receptivity is associated with various glycosylation changes that affect negative charge density at the luminal epithelial cell surface. VZ has been used to monitor the oestrous cycle.

Study Design, Size, Duration: Pathogen-free Jcl:ICR mice, aged 8-10 weeks, were used in this study. We conducted the following three steps to test our hypothesis that VZ may be used to determine uterine receptivity. First, to investigate whether VZ could determine alteration of sulfation and sialylation in the uterine glycocalyx, VZ was measured in mice with induced artificial sulfation and sialylation changes in the uterine glycocalyx (galactose-3-O-sulfotransferase 2 (GP3ST) + α(1,3/1,4) fucosyltransferase gene (FucT-III)-transferred group (n = 15) and in LacZ (encoding for β-galactosidase)-transferred mice as a control group (n = 12)). Second, to investigate whether VZ could determine alterations of the endometrium in preparation for implantation, we measured VZ during the early stage of pregnancy (n = 12 each). Third, to investigate whether VZ could be used to evaluate uterine receptivity prospectively, VZ was measured in an implantation failure model mice. In 21 mice, local and transient suppression of signal transducer and activator of transcription-3 (Stat3) in the uterus were evaluated 1 day before implantation began, and 23 scramble decoy-transferred mice were used as a control group.

Participants/materials, Setting, Methods: The VZ was measured at a frequency of 1 kHz in Jcl:ICR mice. Data were analysed using the Kruskal-Wallis test with Dunn's multiple comparisons, or the Student's t-test or Wilcoxon's rank-sum test with the Shapiro-Wilk normality test. The values of VZ were analysed using receiver operating characteristic (ROC) curve analysis to identify the optimal cut-off point to determine if this parameter predicted non-pregnancy.

Main Results And The Role Of Chance: Sulfation and sialylation changes induced in the luminal epithelial glycocalyx decreased the value of VZ. VZ showed a significant daily decrease during the early stage of pregnancy (Day 1.5 versus 2.5 p.c.: P < 0.005; Student's t-test, Day 2.5 versus 3.5 p.c.: P < 0.001; Wilcoxon's rank-sum test, Day 3.5 versus 4.5 p.c.: P < 0.005; Student's t-test, Day 4.5 versus 5.5 p.c.: P < 0.05; Student's t-test). One day before implantation began, VZ in the implantation failure model mice was significantly higher than in the control mice (P < 0.001, Wilcoxon's rank-sum test). The ROC curve analysis of VZ as a predictor of non-conception showed areas under the ROC curve of 0.91 (95% CI: 0.83-0.99).

Limitations, Reasons For Caution: Although it is influenced by surface charge in the uterine epithelium, the mechanism whereby VZ changes during early pregnancy is still unexplained.

Wider Implications Of The Findings: Local bioelectrical impedance may help to prospectively evaluate uterine receptivity in women. Including the measurement of local bioelectrical impedance as part of a frozen-thawed embryo transfer strategy may improve the efficiency of ART.

Study Funding/competing Interest(s): This work was supported in part by the Japan Society for the Promotion of Science JSPS KAKENHI Grant (Nos. 19390429, 21390453, 16K11086 and 16K11087) from the Ministry of Education, Science and Culture of Japan (Tokyo, Japan) and Suzuken Memorial Foundation (Nagoya, Japan). The authors declare that they have no conflict of interest.