The role of endometrial scratching prior to in vitro fertilization: an updated systematic review and meta-analysis
Authors: Iakovidou Maria Chrysoula , Kolibianakis Efstratios , Zepiridis Leonidas , Venetis Christos 
Published: October 2023

Abstract
Research question
To evaluate the role of endometrial scratching performed prior to an embryo transfer cycle on the probability of pregnancy compared to placebo/sham or no intervention.

Design
A computerized literature (using a specific search strategy) search was performed across the databases MEDLINE, EMBASE, COCHRANE CENTRAL, SCOPUS and WEB OF SCIENCE up to June 2023 in order to identify randomized controlled trials (RCTs) evaluating the effect of endometrial scratching prior to an embryo transfer cycle on the probability of pregnancy, expressed either as live birth, ongoing pregnancy or clinical pregnancy (in order of significance) compared to placebo/sham or no intervention. Data were pooled using random-effects or fixed-effects model, depending on the presence or not of heterogeneity. Heterogeneity was assessed using the I2 statistic. Subgroup analyses were performed based on the population studied in each RCT, as well as on the timing and method of endometrial biopsy. Certainty of evidence was assessed using the GRADEPro tool.

Results
The probability of live birth was significantly higher in embryo transfer cycles after endometrial scratching as compared to placebo/sham or no intervention (relative risk-RR: 1.12, 95% CI: 1.05–1.20; heterogeneity: I2=46.30%, p<0.001, 28 studies; low certainty). The probability of ongoing pregnancy was not significantly difference between the two groups (RR: 1.07, 95% CI: 0.98–1.18; heterogeneity: I2=27.44%, p=0.15, 11 studies; low certainty). The probability of clinical pregnancy was significantly higher in embryo transfer cycles after endometrial scratching as compared to placebo/sham or no intervention (RR: 1.12, 95% CI: 1.06–1.18; heterogeneity: I2=47.48%, p<0.001, 37 studies; low certainty).
A subgroup analysis was performed based on the time that endometrial scratching was carried out. When endometrial scratching was performed during the menstrual cycle prior to the embryo transfer cycle a significantly higher probability of live birth was present (RR: 1.18, 95% CI:1.09-1.27; heterogeneity: I2=39.72%, p<0.001, 21 studies; moderate certainty). On the contrary, no effect on the probability of live birth was present when endometrial injury was performed during the embryo transfer cycle (RR: 0.87, 95% CI: 0.67-1.15; heterogeneity: I2=65.18%, p=0.33, 5 studies; low certainty).
In addition, a higher probability of live birth was only present in women with previous IVF failures (RR: 1.35, 95% CI: 1.20-1.53; heterogeneity: I2=0%, p<0.001, 13 studies; moderate certainty) with evidence suggesting that the more IVF failures the more likely endometrial scratching to be beneficial (p=0.004). The number of times endometrial scratching was performed, as well as the type of instrument used did not appear to affect the probability of live birth.

Conclusions
Endometrial scratching during the menstrual cycle prior to an embryo transfer cycle can lead to a higher probability of live birth in patients with previous IVF failures.

PROSPERO registration
PROSPERO CRD42023433538 (18 Jun 2023)