Application of narrow-band imaging combined with hysteroscopic 7Fr cold knife in the treatment of missed early miscarriage.

Group A had the thickest endometrium (0.99 ± 0.31 cm), whereas group C had the thinnest endometrium (0.55 ± 0.36 cm) 2 weeks after treatment. The time of menstrual resumption after treatment was significantly shorter in Group B than in the other two groups (35.9 0 ± 8.03 days; P  < 0.01). Among the 59 patients in group A, 22 had intrauterine remnants (37.3%), and two had IUA (3.4%); among the 84 patients in group B, one had intrauterine remnants (1.2%), and one had IUA (1.2%); among the 65 patients in group C, four had intrauterine remnants (6.2%), and 11 had IUA (16.9%), with significant differences ( P  < 0.01). No significant differences were observed among the three groups in terms of age, parity, number of pregnancies, number of deliveries, number of miscarriages, amenorrhea duration, gestational sac diameter, blood β-hCG values before and after treatment, the decrease in blood β-hCG multiples 2 weeks after surgery, and BMI ( P  > 0.05). Table 1 Table 1 Comparison of clinical features among the three groups Clinical features A group ( n  = 59) B group ( n  = 84) C group ( n  = 65) F/X 2 P Year (years) 31.95 ± 4.95 30.76 ± 4.21 31.12 ± 4.99 1.133 0.324 Pregnancy (times) 2.46 ± 1.55 2.56 ± 1.63 2.03 ± 1.27 2.422 0.091 Births (times) 0.59 ± 0.72 0.51 ± 0.70 0.37 ± 0.60 1.756 0.175 Vaginal deliveries (times) 0.32 ± 0.54 0.19 ± 0.48 0.17 ± 0.42 1.865 0.157 Cesarean sections (times) 0.28 ± 0.62 0.30 ± 0.62 0.32 ± 0.47 0.810 0.450 Miscarriages (times) 0.85 ± 1.08 1.02 ± 1.32 0.68 ± 0.90 1.724 0.180 Cessation of menstruation (days) 65.93 ± 13.57 69.29 ± 9.63 67.38 ± 8.39 9.503  < 0.01 Gestational sac diameter (cm) 3.30 ± 1.63 1.94 ± 0.67 3.37 ± 1.22 35.101  < 0.01 β hCG Pre treatment (mIU/ml) 37,200.66 ± 10,228.06 19,703.50 ± 15,463.08 35,746.38 ± 33,940.01 2.077 0.128 Β hCG 2 weeks after treatment(mIU/ml) 164.42 ± 62.29 78.32 ± 61.39 133.03 ± 42.42 1.428 0.242 Fold decrease in β hCG 2 weeks after treatment 657.00 ± 1475.81 485.39 ± 588.05 650.26 ± 672.97 0.789 0.46 Endometrial thickness 2 weeks after treatment(cm) 0.99 ± 0.31 0.74 ± 0.37 0.55 ± 0.36 29.597  < 0.01 Menstrual recovery time after treatment(days) 47.19 ± 12.74 35.90 ± 8.03 44.66 ± 13.68 19.793  < 0.01 BMI(kg/m2) 22.53 ± 3.47 22.41 ± 3.26 23.28 ± 3.42 1.34 0.26 Intrauterine Residue(%) 37.3 1.2 6.2 43.88  < 0.01 IUA(%) 3.4 1.2 16.9 15.91  < 0.01 IUA Intrauterine adhesions, BMI Body Mass Index, βhCG serum beta-human chorionic gonadotropin level Comparison of clinical features among the three groups IUA Intrauterine adhesions, BMI Body Mass Index, βhCG serum beta-human chorionic gonadotropin level Clinical data with P  < 0.05 from the one-way analysis were included in a logistic multivariate regression analysis (Table  2 ). The decrease in HCG multiples 2 weeks after treatment, the thickness of the endometrium increases 2 weeks after treatment, the number of days for menstrual recovery increases after treatment, and the treatment method were all factors influencing the occurrence of intrauterine remnants in patients with MEM. The thickness of the endometrium 2 weeks after treatment (OR 17.119, 95% CI 2.742–106.859) and medical abortion (OR 9.068, 95% CI 2.897–28.379) were risk factors for intrauterine remnants, whereas NBI combined with hysteroscopy 7Fr cold knife was a protective factor for intrauterine remnants (OR 0.386, 95% CI 0.019–7.671) (Table  3 ). The treatment method was the only factor influencing the occurrence of IUA in patients with MEM ( P  < 0.05). Medical abortion (OR 0.157, 95% CI 0.032–0.767) and NBI combined with hysteroscopy 7Fr cold knife (OR 0.109, 95% CI 0.012–0.982) were both protective factors for IUA.Tables 4 , 5 Table 2 Univariate logistic regression analysis of Intrauterine Residue after MEM treatment Factor β OR (95%CI) P Year(years) 0.028 1.028 (0.943–1.120) 0.528 BMI(kg/m2) − 0.046 0.955 (0.842–1.083) 0.475 Pregnancy(times) 0.186 1.205 (0.945–1.536) 0.133 Births(times) 0.632 1.882 (1.098–3.228) 0.022 Vaginal deliveries(times) 0.477 1.611 (0.778–3.337) 0.199 Cesarean sections (times) 0.498 1.646 (0.909–2.980) 0.100 Miscarriages(times) 0.140 1.150 (0.829–1.549) 0.402 Cessation of menstruation(times) − 0.036 0.965 (0.928–1.003) 0.071 Gestational sac diameter(cm) 0.176 1.193 (0.900–1.580) 0.219 Β hCG Pre treatment (mIU/ml) 0.000 1.000 (1.000–1.000) 0.510 βhCG 2 weeks after treatment(mIU/ml) 0.002 1.002(1.000–1.003) 0.022 Fold decrease in βhCG 2 weeks after treatment − 0.001 0.999 (0.997–1.000) 0.045 Endometrial thickness 2 weeks after treatment(cm) 2.655 14.229(4.193–48.282)  < 0.001 Menstrual recovery time after treatment(days) 0.109 1.115(1.073–1.159)  < 0.001 Treatment method  Group A 2.205 9.068 (2.897–28.379)  < 0.001  Group B − 1.694 0.069 (0.007–0.698) 0.134  Group C  < 0.001 MEM missed early miscarriage, BMI Body Mass Index, βhCG serum beta-human chorionic gonadotropin level, Group A medical abortion, Group B NBI combined with hysteroscopic 7Fr cold knife, Group C ultrasound-guided vacuum aspiration Table 3 Multivariate logistic regression analysis of Intrauterine Residue after MEM treatment Factor β OR(95%CI) P Births(times) 0.602 1.827 (0.751–4.445) 0.184 βhCG 2 weeks after treatment(mIU/ml) 0.001 1.001 (1.000–1.003) 0.091 Fold decrease in βhCG 2 weeks after treatment − 0.002 0.998 (0.997–1.000) 0.038 Endometrial thickness 2 weeks after treatment(cm) 2.840 17.119 (2.742–106.859) 0.002 Menstrual recovery time after treatment(days) 0.149 1.161 (1.078–1.249)  < 0.001 Treatment method  Group A 1.874 6.513 (1.173–36.166) 0.032  Group B − 0.951 0.386 (0.019–7.671) 0.533  Group C 0.006 MEM missed early miscarriage, βhCG serum beta-human chorionic gonadotropin level, Group A medical abortion, Group B NBI combined with hysteroscopic 7Fr cold knife, Group C ultrasound-guided vacuum aspiration Table 4 Univariate logistic regression analysis of IUA after MEM treatment Factor β OR(95%CI) P Year (years) 0.082 1.085 (0.969–1.216) 0.157 BMI (kg/m2) 0.012 1.012 (0.863–1.186) 0.886 Pregnancy (times) − 0.039 0.962 (0.664–1.394) 0.838 Births (times) − 0.151 0.860 (0.372–1.991) 0.725 Vaginal deliveries (times) − 0.032 0.968 (0.307–3.049) 0.956 Cesarean sections (times) − 0.201 0.818 (0.287–2.328) 0.706 Miscarriages (times) − 0.007 0.993 (0.614–1.605) 0.987 Cessation of menstruation (times) 0.046 1.047 (0.997–1.099) 0.067 Gestational sac diameter (cm) 0.514 1.672 (1.169–2.393) 0.005 β hCG Pre treatment (mIU/ml) 0.000 1.000 (1.000–1.000) 0.155 βhCG 2 weeks after treatment(mIU/ml) 0.000 1.000 (0.998–1.002) 0.908 Fold decrease in βhCG 2 weeks after treatment 0.000 1.000 (.999–1.001) 0.920 Endometrial thickness 2 weeks after treatment(cm) − 2.171 0.114 (0.012–1.058) 0.056 Menstrual recovery time after treatment(days) 0.039 1.039 (0.999–1.081) 0.054 Treatment method  Group A − 1.759 0.172 (0.036–0.8139) 0.026  Group B − 2.828 0.059 (0.007–0.471) 0.008  Group C 0.005 MEM missed early miscarriage, βhCG serum beta-human chorionic gonadotropin level, Group A medical abortion, Group B NBI combined with hysteroscopic 7Fr cold knife, Group C ultrasound-guided vacuum aspiration Table 5 Multivariate logistic regression analysis of IUA after MEM treatment Factor β OR(95%CI) P Gestational sac diameter(cm) 0.397 1.488 (0.954–2.320) 0.080 Treatment method  Group A − 1.849 0.157 (0.032–0.767) 0.022  Group B − 2.220 0.109 (0.012–0.982) 0.048  GroupC 0.014 MEM missed early miscarriage, IUA Intrauterine adhesions, Group A medical abortion, Group B NBI combined with hysteroscopic 7Fr cold knife, Group C ultrasound-guided vacuum aspiration Univariate logistic regression analysis of Intrauterine Residue after MEM treatment MEM missed early miscarriage, BMI Body Mass Index, βhCG serum beta-human chorionic gonadotropin level, Group A medical abortion, Group B NBI combined with hysteroscopic 7Fr cold knife, Group C ultrasound-guided vacuum aspiration Multivariate logistic regression analysis of Intrauterine Residue after MEM treatment MEM missed early miscarriage, βhCG serum beta-human chorionic gonadotropin level, Group A medical abortion, Group B NBI combined with hysteroscopic 7Fr cold knife, Group C ultrasound-guided vacuum aspiration Univariate logistic regression analysis of IUA after MEM treatment MEM missed early miscarriage, βhCG serum beta-human chorionic gonadotropin level, Group A medical abortion, Group B NBI combined with hysteroscopic 7Fr cold knife, Group C ultrasound-guided vacuum aspiration Multivariate logistic regression analysis of IUA after MEM treatment MEM missed early miscarriage, IUA Intrauterine adhesions, Group A medical abortion, Group B NBI combined with hysteroscopic 7Fr cold knife, Group C ultrasound-guided vacuum aspiration The ROC curve was plotted to jointly predict the occurrence of retained products of conception after treatment using the time to menstrual recovery post-treatment, endometrial thickness at 2 weeks post-treatment, and β-HCG levels. The AUC was 0.926 (95% CI: 0.876–0.975), with a sensitivity of 92.6%, specificity of 87.2%, and a Youden index of 0.744, indicating good predictive performance (Fig.  2 ). Fig. 2 ROC curve predictive performance ROC curve predictive performance

This retrospective cohort study was approved by the Ethics Committee of Hubei Province Women and Children Hospital (no. 2023IEC093). All patients signed informed consent before treatment, and neither patients nor the public were involved in the design, implementation, reporting, or dissemination of this research plan. A total of 208 patients who underwent treatment for MEM at the Department of Obstetrics and Gynecology of Hubei Maternal and Child Health Hospital from January 2023 to June 2023 were retrospectively selected. Because of the larger size of the uterus in pregnancies exceeding 8 weeks, the risk of bleeding after embryo removal increases, and the larger gestational sac is challenging to completely remove in a few attempts using the 7Fr cold knife instrument, which may increase the risk of complications. Therefore, the gestational age of the gestational sacs in the patients with MEM included in this study was all less than 8 weeks. As the largest tertiary specialized hospital in Hubei Province, China, over 1500 patients with MEM are admitted annually. A total of 746 cases of patients with MEM who received treatment at our hospital during the same period were identified using the hospital’s internal database. According to the inclusion and exclusion criteria, 208 patients were ultimately included using a computer-generated random number method (Fig.  1 ). Fig. 1 The inclusion and grouping process for women in MEM. MEM missed early miscarriage, MA medical abortion group, NBI  +  7Fr narrow-band imaging combined with hysteroscopic 7Fr cold knife group, UVA ultrasound-guided vacuum aspiration group The inclusion and grouping process for women in MEM. MEM missed early miscarriage, MA medical abortion group, NBI  +  7Fr narrow-band imaging combined with hysteroscopic 7Fr cold knife group, UVA ultrasound-guided vacuum aspiration group The inclusion criteria included: (1) amenorrhea not exceeding 12 weeks; (2) ultrasound gestational age ≤ 8 weeks; (3) early pregnancy missed abortion confirmed by clinical and ultrasound examination[ 12 – 14 ]. The exclusion criteria included: (1) incomplete patient information or refusal to follow-up; (2) multiple pregnancies; (3) suspected trophoblastic disease; (4) massive active vaginal bleeding; (5) other diseases affecting normal uterine morphology, such as uterine fibroids and adenomyosis; (6) contraindication to mifepristone use; (7) presence of an intrauterine device. Patients with MEM were classified into three groups based on the method of abortion used: (1) Group A (medical abortion group): Patients took 50 mg mifepristone orally 2 h before meals, once every 12 h, for three doses, completing oral mifepristone within 2 days. On the morning of the third day, they switched to oral 0.6 mg misoprostol. Six hours after taking misoprostol, another 0.4 mg of misoprostol was given orally if the products of conception were not expelled and vaginal bleeding was less than menstrual flow. Successful medical abortion was defined as the expulsion of the gestational sac without the need for surgical intervention. (2) Group B (NBI combined with hysteroscopic 7Fr cold knife group): Patients followed the same mifepristone oral administration method as the medical abortion group; however, they did not take misoprostol to avoid bleeding that could interfere with the hysteroscopic view. After uterine distention with hysteroscopy, the gestational sac was observed, and the uterine cavity was observed again after targeted suction of the gestational sac under negative pressure. If residual tissues were present, a 7Fr micro-forceps was inserted through the instrument channel (KMS, 30° sheath-integrated hysteroscope, with a 5.4 mm diameter lens) to grasp the remaining tissue. The NBI mode was used to observe the attachment site of the original gestational sac (Olympus electronic hysteroscope system, equipped with a xenon light source, providing both white light imaging and NBI modes). The procedure ended when no residual trophoblastic tissue was observed, and no negative pressure was applied to remove decidual tissue in non-gestational sac attachment sites. (3) Group C (ultrasound-guided suction group): Patients followed the same mifepristone oral administration method as the medical abortion group without taking misoprostol. Under ultrasound guidance, an appropriate suction tube was used to perform negative pressure suction on the gestational sac, with a negative pressure of < 500 mmHg. The uterine cavity was suctioned clockwise 1–2 times, and the surgery was completed after rinsing and suctioning out typical trophoblastic tissue. The operators for Groups B and C were the same experienced deputy chief physicians in the Department of Obstetrics and Gynecology to ensure consistency in the procedures. All patients underwent follow-up transvaginal ultrasound and blood beta-human chorionic gonadotropin (β-HCG) level measurement 14 days postoperatively to record endometrial thickness. The patients underwent a second follow-up with a three-dimensional ultrasound after 45 days to assess intrauterine residue or uterine adhesions [ 15 – 17 ]. Each patient was followed up for at least until the third menstrual period after the procedure. Patients who did not menstruate within three months postoperatively or had significantly reduced menstrual flow underwent hysteroscopy to diagnose the presence of uterine adhesions. Clinical data collected from the patients included age, gravidity, parity, number of miscarriages, weeks of amenorrhea, maximum diameter of the gestational sac, body mass index (BMI), endometrial thickness 2 weeks postoperatively, the magnitude of blood β-HCG decrease 2 weeks postoperatively, and the time of menstrual return postoperatively. SPSS 20.0 was used for data analysis. Kurtosis and skewness tests were used to determine whether the metric data were normally distributed. Normally distributed metric data are represented as the mean ± standard deviation. One-way analysis of variance was used. Count data were represented by percentages (%), and Chi-square and Fisher’s exact tests were used. Logistic regression models were used to obtain the odds ratios (ORs) and coefficients of various indicators that influence post-MEM treatment complications and to establish regression equations. The receiver operating characteristic (ROC) curve was plotted to assess the predictive value of complications associated with MEM. The ROC curves for each indicator and the combined predictive factors for complications were drawn, and the area under the curve (AUC) was calculated. An AUC > 0.5 indicated predictive value, AUC > 0.7 indicated moderate accuracy in prediction, and AUC > 0.9 indicated good predictive accuracy. P < 0.05 was considered statistically significant.

The combination of NBI and a 7Fr cold knife hysteroscopy for the treatment of MEM is safe and effective. This approach protects the endometrium, promotes rapid menstrual recovery, and results in lower post-operative intrauterine retention and adhesion rates. Furthermore, it can reduce the psychological burden on patients and the economic costs associated with post-operative complications. A prospective randomized controlled trial will be designed, and long-term follow-ups with patients will be conducted.

To the best of our knowledge, this study is the first to combine NBI with the 7Fr cold knife hysteroscope for the treatment of MEM. The primary treatment methods for early pregnancy missed abortion are medical abortion (MA) and ultrasound-guided uterine vacuum aspiration (UVA). MA is used to terminate pregnancy using oral medications, suitable for women diagnosed with intrauterine pregnancy, with a gestational age of ≤ 70 days, without contraindications to MA, and who voluntarily request MA [ 18 ]. The advantages of MA include no need for surgery, minimal injury, and less pain; however, it has an intrauterine retention rate of approximately 15.5%, a longer treatment duration, and risks of heavy vaginal bleeding [ 19 , 20 ]. In this study, the intrauterine retention rate for patients undergoing medical abortion reached 37.3%, higher than that reported in the literature. This result may be related to tissue degeneration, necrosis, and organization associated with MEM, as well as adhesions to the uterine wall. Vacuum aspiration is required for further treatment if the retained intrauterine tissue cannot be expelled on its own. However, vacuum aspiration in patients with MEM is more challenging than in normal cases, as densely adhered retained tissue can easily damage the basal layer of the endometrium owing to prolonged and repeated manipulation, leading to IUA [ 21 – 23 ]. The incidence of IUA after vacuum aspiration in early pregnancy patients can reach 15% [ 24 ]. Additionally, women who underwent vacuum aspiration twice or more had a twofold increased risk of IUA compared to those who had it once [ 25 ]. Repeated vacuum aspiration can cause damage to the basal layer of the endometrium [ 26 ], leading to fibrous connective tissue hyperplasia and endometrial regeneration disorders, causing impaired endometrial repair and IUA. IUA can severely harm women’s reproductive function and affect their reproductive physiology and mental health, and moderate to severe IUA typically has poor treatment outcomes [ 27 ]. In this study, the incidence of IUA after ultrasound-guided vacuum aspiration was 16.9%, similar to the results reported previously. Therefore, identifying an appropriate treatment method to reduce the incidence of intrauterine retention and IUA after pregnancy termination in patients with MEM is essential. Recently, hysteroscopic curettage has been applied in clinical practice. Compared to ultrasound guidance, the primary advantage of hysteroscopy is the ability to visually observe the gestational sac. After targeted suction of the gestational sac under direct vision, the endometrium can be examined under NBI. If dense, tortuous, and dilated spiral green vessels are observed near the original attachment site of the gestational sac (Figs.  3 A), small residual chorionic tissue may be present. At this point, a 7Fr cold knife with grasping devices can be inserted to clamp and remove these vessels, disrupting the blood supply to the micro-residual pregnancy tissue (Figs.  3 B, C ). The advantage of this method is that NBI can accurately locate residual chorionic tissue that has a blood supply and is not easily detected. Additionally, the 7Fr hysteroscopic cold knife can directly remove the residual tissue without the need for frequent instrument changes or re-entering the uterine cavity, thus avoiding additional negative pressure suction on the endometrium and protecting the endometrium (Fig.  3 D). Micro scissors can also be inserted to cut the adhesions for patients with MEM and existing IUA, enabling the diagnosis and treatment of mild to moderate IUA. Notably, targeted negative pressure suction was still used while performing hysteroscopic suction of the gestational sac because the 7Fr cold knife instrument cannot completely grasp the entire gestational sac, and repeated grasping can increase operation time and the risk of hysteroscopy-related complications. In contrast, negative pressure suction of the gestational sac typically only takes a few seconds and requires low negative pressure. This method causes almost no damage to most of the endometrium at non-implantation sites and can also detect abnormalities in the uterine cavity, such as uterine septum, polyps, and fibroids [ 28 ]. Fig. 3 A NBI combined with hysteroscopic chorionic blood vessels and pregnancy residual tissue. B Chorionic blood vessels and residual tissues of pregnancy under white light of hysteroscopy. C Destruction of villous vessels with 7fr cold knife clamp under hysteroscopy. D Uterine cavity after pregnancy tissue removal A NBI combined with hysteroscopic chorionic blood vessels and pregnancy residual tissue. B Chorionic blood vessels and residual tissues of pregnancy under white light of hysteroscopy. C Destruction of villous vessels with 7fr cold knife clamp under hysteroscopy. D Uterine cavity after pregnancy tissue removal Intrauterine retention is one of the common complications after MEM treatment. The pathological manifestation of intrauterine retention is chorionic tissue, primarily derived from the tertiary chorionic stalk formed during embryonic development, which contains abundant connective tissue and capillaries. After pregnancy termination, the residual chorionic tissue exhibits increased vascularization and worsened vascular wall fibrosis, with high echogenic masses or high blood flow signals in the endometrium [ 29 ]. Patients undergoing hysteroscopic curettage have lower rates of intrauterine retention and IUA than those undergoing vacuum aspiration under ultrasound guidance, with higher rates of subsequent pregnancies and quicker post-operative conception [ 7 , 9 ]. In this study, patients treated with a 7Fr cold knife combined with NBI after MEM had earlier menstrual recovery and lower intrauterine retention and IUA rates than the other two groups, indicating that this method can better protect the endometrium and facilitate earlier pregnancy planning for patients after treatment. UVA requires several weeks of aspiration in the uterine cavity, inevitably causing some damage to the endometrial tissue at non-implantation sites, one of the inducing factors for IUA after artificial abortion [ 30 ]. In this study, the incidence of IUA in patients treated with NBI combined with a 7Fr cold knife hysteroscopy was 1.2%, lower than the 3.4% observed in the medical abortion group and significantly lower than the 16.9% in the ultrasound-guided vacuum aspiration group. The surgeon’s view may sometimes be obscured by bleeding or thick surrounding decidua when using hysteroscopy alone for targeted low negative pressure suction of the gestational sac, leading to repeated intrauterine manipulations on indistinct residual tissue, causing damage to the endometrium and resulting in IUA, or prematurely terminating the procedure, leading to intrauterine retention. NBI enhances the contrast by allowing the hemoglobin in red blood cells within the vascular surface of the tissue to strongly absorb blue–green light. In contrast, the non-vascular areas of the mucosal surface reflect this light strongly, enabling clearer observation of micro-residual chorionic tissue and its blood supply. The grasping force of the 7Fr cold knife instrument for residual tissue is also significantly greater than that of the 5Fr outpatient hysteroscope, allowing for rapid, targeted removal of the target tissue, reducing the operation time, and lowering the risk of hysteroscopic fluid overload. Notably, hysteroscopy may not improve reproductive outcomes compared to negative pressure suction [ 31 – 34 ]. Additionally, the medical costs associated with hysteroscopic embryo retrieval are higher than those for medical abortion and ultrasound-guided negative pressure suction. The completion of the procedure is not always feasible in all cases, and incomplete surgery and fluid overload remain risks. Although fluid overload did not occur in this study, this potential risk should be communicated to patients in advance. This study has some limitations as it was a single-center retrospective analysis with a relatively small number of included patients, and it lacked longer-term follow-up, resulting in some long-term complications being undetected. Additionally, the study did not include data on the time to subsequent pregnancy and reproductive outcomes.

Missed early miscarriage (MEM) is the condition in which an ultrasound examination determines the cessation of the intrauterine gestational sac or embryonic growth or the disappearance of the fetal heart with retained pregnancy tissues before 12 weeks of gestation [ 1 ]. The occurrence rate of complications such as intrauterine residue and intrauterine adhesion (IUA) at the termination of MEM pregnancy is significantly higher than in normal pregnancy, and complications can exacerbate the physical, psychological, and economic burden on patients [ 2 ]. Uterine aspiration can lead to IUA in 15% of patients [ 3 ]. Compared to uterine aspiration, medical abortion is considered safe and convenient, and it does not cause IUA owing to damage to the functional layer of the endometrium [ 4 ]. However, 1–3% of patients undergoing medical abortion may experience incomplete miscarriage, of which 2% may have anemia and hemorrhagic shock owing to vaginal bleeding [ 5 ]. Therefore, a better treatment method for MEM that can remove the gestational tissue, reduce the risks of intrauterine retention and heavy bleeding, and lower the risks of endometrial damage and IUA is urgently required. Hysteroscopy has been gradually used to treat MEM because it allows for intrauterine procedures under direct vision [ 6 ]. However, its effectiveness remains unclear. Some studies suggest that hysteroscopic surgery better preserves endometrial tissue than dilatation and curettage (uterine vacuum aspiration), resulting in lower intrauterine retention and IUA rates, higher subsequent pregnancy rates, and faster post-operative conception [ 7 – 9 ]. Conversely, Cyrille et al. observed no difference in reproductive outcomes between hysteroscopic surgery and uterine aspiration [ 10 ]. Therefore, a key challenge for hysteroscopists is to enhance direct-vision procedures, enabling precise gestational tissue extraction with minimal damage while preserving the endometrium as effectively as medical abortion. Narrow-band imaging (NBI) is a novel endoscopic image enhancement technology that can clearly display the fine structure of superficial mucosa and highlight the microvascular morphology of lesions. This technique can improve lesion detection rates and diagnostic accuracy and is commonly used in gynecology to diagnose endometrial lesions [ 11 ]. The 7Fr cold knife hysteroscope is an integrated 30° hysteroscope with a shaft diameter of 5.4 mm. It has a working channel that can accommodate auxiliary instruments, such as grasping forceps and micro scissors, for tissue retrieval within the uterine cavity. The diameter of commonly used 5Fr outpatient hysteroscopy accessory instruments is 1.6 mm, whereas that of the 7Fr hysteroscope accessories is 2.2 mm, allowing for a larger grasping area, greater force, and less deformation of instruments. Cervical dilation is not generally required, resulting in minimal tissue damage to the cervix. However, no studies have reported the application of NBI for MEM treatment. By using the advantages of NBI in vascular imaging and the operational flexibility of the 7Fr cold knife hysteroscope, this study aimed to make hysteroscopic procedures more adaptable and precise, thereby reducing the incidence of intrauterine retention and IUA while protecting the endometrium.