3D Vascularity: A Novel Predictor of FET Success?
Corresponding Author: Rashmi Vohra, Department of Reproductive Medicine & Surgery, Sri Ramachandra Institute of Higher Education and Research, Chennai, Tamil Nadu, India, Phone: +91 7986277843, e-mail: email@example.com
Introduction: Endometrial blood flow reflects uterine receptivity. A study was done to look for a better predictor of endometrial receptivity with a novel 3D technique.
Materials and Methods: Prospective cohort study was done on 203 women undergoing frozen embryo transfer (FET) cycles in a tertiary care center for a period of 2 years from November 2018 to November 2020 to see the correlation of endometrial and subendometrial blood flow assessed by 3D power Doppler. Various indices endometrial volume, subendometrial volume and their vascularization index (VI), flow index (FI), and vascularization flow index (VFI) were obtained and compared between the pregnant and nonpregnant groups. The primary outcome was clinical pregnancy and ongoing pregnancy rates.
Results: Out of 203 patients, 121 patients achieved pregnancy with a pregnancy rate of 59.6%. The endometrial and subendometrial volume was comparable between the two groups. Endometrial VI (3.3 ± 1.2 vs 2.8 ± 0.6; p < 0.01), FI (24.9 ± 3.0 vs 23.1 ± 2.7; p < 0.01) and VFI (1.4 ± 0.5 vs 1.1 ± 0.3; p < 0.01) were significantly higher in pregnant as compared to nonpregnant group. There was a significant difference in subendometrial VI (5.2 ±1.5 vs 4.4 ±1.9; p < 0.01), FI (26.0 ± 3.5 vs 25.0 ± 3.7; p = 0.04) and VFI (2.7 ± 1.1 vs 2.2 ± 0.6; p < 0.01) between two groups. Receiver operating characteristic (ROC) curves were plotted for these parameters and cut-off values were calculated. At the cut-off value of endometrial VFI of 1.18, gave sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of 71.9%, 75.6%, 81.3%, 64.5%, and 73.4%, respectively while at the cut-off value of subendometrial VFI of 2.35, gave sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of 66.9%, 63.4%, 72.9%, 56.5%, and 65.5%, respectively. A cut-off value of endometrial VFI of 1.18 and subendometrial VFI of 2.35, gave ongoing pregnancy rates of 67.3% and 59.5%, respectively.
Conclusion: Endometrial and subendometrial vascularity by 3D power Doppler can be a useful novel parameter in predicting pregnancy in FET cycles.
How to cite this article: Vohra R, Pandurangi M, Nellepalli SR, et al. 3D Vascularity: A Novel Predictor of FET Success? Int J Infertil Fetal Med 2022;13(2):67-71.
Source of support: Nil
Conflict of interest: None
Keywords: Cohort study, Embryo transfer, Infertility, Pregnancy rates, 3D power Doppler
Frozen embryo transfer accounts for 45–50% of all childbirths in ART.1 Various methods have been adopted for the evaluation of endometrial receptivity. Noninvasive methods include assessment of endometrial thickness and volume, endometrial blood flow, endometrial pattern, Doppler study of uterine arteries and. The accuracy of the 3D volume assessment method is more than the 2D-volume estimation, with an error estimation of 7% and 22%, respectively.2 Angiogenesis plays an important role in reproductive processes such as follicle growth, corpus luteum formation, endometrial growth, and implantation. A good endometrial blood supply is an essential requirement for implantation. So, do the endometrial and subendometrial blood flows measured by 3D power Doppler ultrasound have any role as the predictive factors for pregnancy during FET cycles?
To date, very few studies have reported on this question and it needs further evaluation. With this in mind, the present prospective study was designed to study the role of endometrial and subendometrial blood flows measured by 3D power Doppler ultrasound in artificially programed FET cycles.
Aims and Objectives
To study the role of endometrial and subendometrial blood flow measured by 3D power Doppler as predictors of pregnancy in FET cycles.
Primary objective: To study the role of endometrial and subendometrial blood flow measured by 3D power Doppler on clinical pregnancy rates in patients undergoing frozen thawed embryo transfer cycle.
Secondary objective: To study the role of endometrial and subendometrial blood flow measured by 3D power Doppler on miscarriage rate and ongoing pregnancy rate till 20 weeks of gestation in patients undergoing frozen-thawed embryo transfer cycle.
MATERIALS AND METHODS
It was a prospective cohort study done on 203 patients in the department of Reproductive Medicine & Surgery, Sri Ramachandra Institute of Higher Education and Research, Chennai (India) for a study period of 2 years from November 2018 to November 2020. All patients undergoing the frozen-thawed embryo transfer cycle were included with the following selection criteria:
All female patients undergoing frozen-thawed embryo transfer
Patients providing written and informed consent.
Uncorrected uterine factor: Fibroids, polyps, diffuse adenomyosis
Institutional Ethical Committee approval was obtained.
Reference number: CSP-MED/19/JAN/49/14.
Combined estrogen progestin (CEP) pills (T. Ovral L, Pfizer Ltd.–Ethinyl Estradiol 30 mcg + Levonorgestrel 0.15 mg) were started on days 2–5 of the cycle for a period of 21 days. On the 15th day of CEP pills, Inj Leuprolide Acetate 3.75mg Depot (Inj Leupride Depot 3.75 mg, Sun Pharmaceutical Industries Ltd) was given. On day 5 of withdrawal bleeding, TVS was done. In patients with endometrial thickness <5 mm & bilateral suppressed ovaries (no anechoic cystic structure >10 mm), decision to start hormone replacement therapy was taken. Estradiol Valerate was started in the dose of 4 mg/day (2 mg BD, orally) for 5 days followed by 6 mg/day (2 mg TDS, orally) for 6 days. After 11 days of estradiol valerate, the patient was reviewed. Transvaginal sonography was done to assess endometrial thickness, pattern, blood flow, and volume. If endometrial thickness ≥7 mm, the decision to start progesterone was taken after completing 14 days of estradiol valerate.
On the day of starting progesterone, endometrial assessment is done using an endocavity transducer 4–10 MHz bandwidth (RIC 5–9A–RS, GE Voluson S8 BT 16). On 2D ultrasound, endometrial thickness, endometrial pattern, and zones of vascularity were assessed.
The ultrasound machine switched to 3D mode with power Doppler. The sector of interest covering endometrial cavity in a longitudinal plane of the uterus was adjusted, and the sweep angle was set to 90 to ensure that a complete uterine volume including the entire subendometrium could be obtained as shown in Figure 1.
The power Doppler characteristics set were: a color gain of 5, pulse repetition frequency of 0.3 Khz, and wall motion filter of 60 Hz.
3D volume acquired keeping patient and 3D transvaginal probe as static as possible. Endometrial volume was measured using a virtual organ computer-aided analysis (VOCAL) imaging program. VOCAL is the combination of 3D ultrasound tissue presented as voxels and geometric information of surfaces in a 3D dataset. It is defined by rotating an image plane around a fixed axis and defining 2D contours of each plane. The 2D contours of the polygonal area in each plane can be defined automatically or manually. There are four rotation angles to choose from 6°, 9°, 15°, and 30°, and because the entire dataset is rotated at about 180°, these result in 30, 20, 12, and 6 planes, respectively, is available for measurements. The result is converted to mL or cm ultrasound units3 In the present study six contour planes were analyzed with a 30° rotation step for endometrium to cover 180°.
Volume histogram was obtained to measure endometrial volume, vascularization index (VI), flow index (FI), and vascularization flow index (VFI) as shown in Figure 2.
Following the assessment of the endometrial vascularity, shell-imaging was used to measure subendometrial blood flow within the 2-mm shell of endometrial myometrial contour as shown in Figure 3.
Vascularization index, FI, and VFI of subendometrial region were obtained.
The vascularization index (VI) represents the presence of blood vessels (vascularity) in the endometrium. It is measured as the ratio of the number of color voxels to the total number of voxels and is expressed as a percentage (%) of the endometrial volume.
Flow index (FI) is the mean power Doppler signal intensity inside the endometrium and represents the average intensity of flow.
Vascularization flow index (VFI) is a combination of vascularity and flow intensity.
After completing the endometrial assessment, progesterone supplementation was started. Inj Micronised Progesterone 100 mg intramuscularly (Inj Susten, Sun Pharma Industries Ltd) once a day was given between 8:00 am and 12:00 pm. The duration of progesterone supplementation was dependent on the day of embryo was available for transfer. The day of Embryo transfer and the number of embryos to be transferred were based on departmental protocol.
If ET <7 mm, a dose of estradiol valerate was gradually increased by 2 mg/day (orally) every 5 days. The transvaginal scan was repeated every 5 days. If ET was a suboptimal gradual increment of oral dose continued till a maximum dose of 12 mg/day was reached. Even after maximum oral dose of estradiol valerate, if ET remained suboptimal, oral supplementation was continued and vaginal administration was started at the dose of 4 mg/day. The dose was gradually increased by 2 mg/day every 5 days. Transvaginal scan was repeated every 5 days. If ET was suboptimal gradual increment of vaginal dose continued till a maximum dose of 12 mg/day was reached. If endometrial thickness was <7 mm after maximum dose of estradiol valerate (12 mg/day- Orally and 12 mg/day vaginally) decision for embryo transfer or cycle cancellation was taken after explaining the couple. After embryo transfer, same dose of estradiol valerate was continued. Micronized Progesterone (Cap. Susten 200 mg, Sun Pharmaceutical Industries Ltd) 600 mg/day (200mg TDS, per vaginally) and Dydrogesterone (Tab. Duphaston 10 mg, Abbott) 30 mg/day (10 mg TDS, orally) were started. Serum Beta HCG was done 2 weeks after embryo transfer. If beta HCG > 5 IU/L, then an ultrasound was done after 2 weeks (i.e., 4 weeks after embryo transfer) to look for presence, number and location of gestational sac, and cardiac activity. Daily progesterone for luteal support was continued till 12 weeks of gestation. Patients were followed up till 20 weeks gestational age. The primary endpoint assessed was the ongoing pregnancy rate. The secondary endpoints assessed were pregnancy rate, biochemical pregnancy rate, clinical pregnancy rate, and miscarriage rate.
The collected data will be analyzed with IBM SPSS statistics software 23.0 Version. To describe the data descriptive statistics frequency analysis, percentage analysis will be used for categorical variables, and for continuous variables the mean and SD will be used. To find the significant difference between the bivariate samples in independent groups the unpaired sample t-test or Mann-Whitney U test will be used as on the normality of the data. To find the association of significance in categorical data the Chi-square test or Fisher’s exact test will be used. In all the above statistical tools, the probability value of 0.05 will be considered a significant level.
OBSERVATIONS AND RESULTS
We conducted a prospective cohort study to see the correlation of endometrial and subendometrial vascularity by 3D power Doppler with clinical outcomes in frozen-thawed embryo transfer cycles in 203 women satisfying the inclusion and exclusion criteria.
To see the correlation of endometrial and subendometrial vascularity by 3D power Doppler with clinical outcomes in frozen-thawed embryo transfer cycles we divided the patients into pregnant and nonpregnant groups and compared the baseline and ultrasound characteristics. Out of 203 patients, 121 patients achieved pregnancy with a pregnancy rate of 59.6%. The two groups were comparable in terms of age, duration of infertility, and type of infertility.
Female factor was the most common cause of infertility in patients who conceived while malefactor was the most common cause of infertility in patients who could not achieve pregnancy.
Body mass index, FET cycle characteristics, number, and day of embryo transferred were comparable in both the groups.
Almost a similar number of embryos were transferred in both groups. The groups were comparable in terms of the type of embryo transfer. The total duration of HRT was significantly higher in nonpregnant cycles.
The endometrial thickness and volume was comparable between the two groups (9.7 ± 1.4 vs 9.8 ± 1.6; p = 0.83 and 2.9 ± 0.8 vs 2.7 ± 0.7; p = 0.17, respectively). Endometrial VI (3.3 ± 1.2 vs 2.8 ± 0.6; p < 0.01), FI (24.9 ± 3.0 vs 23.1 ± 2.7; p < 0.01), and VFI (1.4 ± 0.5 vs 1.1 ± 0.3; p < 0.01) were significantly higher in pregnant as compared to non-pregnant group. There was a significant difference in subendometrial VI (5.2 ±1.5 vs 4.4 ±1.9; p < 0.0 1), FI (26.0 ± 3.5 vs 25.0 ± 3.7; p = 0.04) and VFI (2.7 ± 1.1 vs 2.2 ± 0.6; p < 0.01) between two groups. Vascularity parameters are summarized in Table 1.
|Pregnant (121)||Nonpregnant (82)||p-value|
|1||Endometrial thickness||9.7 ± 1.4||9.8 ± 1.6||0.83|
|2||Endometrial volume (mL)||2.9 ± 0.8||2.7 ± 0.7||0.17|
|3||Endometrial VI (%)||3.3 ± 1.2||2.8 ± 0.6||0.001|
|4||Endometrial FI (0–100)||24.9 ± 3.0||23.1 ± 2.7||0.001|
|5||Endometrial VFI (0–100)||1.4 ± 0.5||1.1 ± 0.3||0.001|
|6||Subendometrial VI (%)||5.2 ± 1.5||4.4 ± 1.9||0.01|
|7||Subendometrial FI (0–100)||26.0 ± 3.5||25.0 ± 3.7||0.04|
|8||Subendometrial VFI (0–100)||2.7 ± 1.1||2.2 ± 0.6||0.01|
|Cut-off||Sensitivity||Specificity||Positive predictive value||Negative predictive value||Diagnostic accuracy|
|2||Endometrial volume (mL)||2.77||49.59%||52.00%||60.61%||41.35%||50.74%|
|3||Endometrial VI (%)||2.85||65.29%||62.20%||71.82%||54.84%||64.04%|
|4||Endometrial FI (0–100)||23.41||70.20%||63.40%||73.91%||59.09%||67.49%|
|5||Endometrial VFI (0–100)||1.18||71.90%||75.60%||81.31%||64.58%||73.40%|
|6||Subendometrial VI (%)||4.53||61.98%||62.20%||70.75%||52.58%||62.07%|
|7||Subendometrial FI (0–100)||24.59||57.90%||48.80%||62.50%||43.96%||54.19%|
|8||Subendometrial VFI (0–100)||2.35||66.90%||63.40%||72.97%||56.52%||65.52%|
At cut-off value of endometrial VFI of 1.18, gave sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of 71.9%, 75.6%, 81.3%, 64.5%, and 73.4%, respectively to predict pregnancy while at cut-off value of subendometrial VFI of 2.35, gave sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of 66.9%, 63.4%, 72.9%, 56.5%, and 65.5%, respectively in order to predict pregnancy. A cut-off value of endometrial VFI of 1.18 and subendometrial VFI of 2.35, gave ongoing pregnancy rates of 67.3% and 59.5%, respectively. One pregnancy was terminated at 18 weeks in view of tetralogy of Fallot diagnosed in the fetus.
It is a matter of debate whether the assessment of endometrial or subendometrial vascularity measured by 3D power Doppler in frozen-thawed embryo transfer cycles can predict and help in the improvement of pregnancy outcomes. Despite the advent of FET in the early 1980s, and continuous increase in its usage in assisted reproduction over three decades, with about half of all embryos, transferred being frozen-thawed embryos, only a little research has been done on the role of endometrial and subendometrial vascularity by 3D power Doppler in FET cycles outcomes.
Endometrial microvascular blood flow determined in the early luteal phase of the cycle preceding an IVF cycle has been shown to be predictive of pregnancy. In a study by Jinno et al., they showed significantly higher chances of pregnancy in women with endometrial tissue blood flow of more than 29 mL/ min per 100 gm of tissue as compared to women with lower values.3 3D ultrasound power Doppler provides a novel noninvasive tool to examine the blood supply towards the endometrium and the subendometrial region.
3D power Doppler angiography of the uterus involves the acquisition and measurement of power Doppler data within a 3D data set. Embryo wastage can be avoided with this novel technique by identifying when the endometrium is in a better receptive state. The “histogram” tool uses specific algorithms to derive indices of blood flow and display the distribution of the power Doppler data. Several settings determine the intensity of the power Doppler spectrum: gain, pulse repetition frequency (PRF), line density, wall motion filter, signal rise, and persistence and speed of acquisition.4
Endometrial and subendometrial layer vascularity parameters have been compared between pregnant and nonpregnant cycles in many studies. Different studies have found different results. Wu et al. found significantly higher subendometrial vascularity in pregnant IVF cycles5 while Ng et al. found that the vascularity of endometrial and subendometrial layers measured by 3D power Doppler ultrasound was not a good predictor of pregnancy. Ng et al. studied the same in natural or stimulated cycle frozen embryo transfers6 Maugey-Laulom et al. concluded that the presence of sub- and intraendometrial vascularity on the day of ET seemed to be an important parameter for obtaining ongoing pregnancy.7 A prospective observational study by Kim et al. on 234 women (pregnant group (n = 113) or a nonpregnant group (n = 121) undergoing first IVF-ET using a GnRH long protocol with stimulation by recombinant FSH underwent color Doppler ultrasound and 3D PD-US examinations on the day of embryo transfer. Higher endometrial VI, FI, and VFI values were seen in pregnant group than the nonpregnant group (p = 0.001, p = 0.000, p = 0.021, respectively) while subendometrial region VI, FI, and VFI scores (p = 0.770, p = 0.252, p = 0.451), did not differ between groups. Endometrial VI, FI, and VFI scores cut-off values were 0.95, 12.94, and 0.15 for pregnancy achievement.8 Mishra et al. showed a positive correlation of subendometrial and endometrial blood flows with pregnancy rates.9 Similarly in our study, endometrial and subendometrial vascularity parameters were significantly higher in the pregnant group as compared to the nonpregnant group.
Strengths of Our Study
Prospective study design.
Study enrolment criteria were strictly followed.
Uniform method of endometrial preparation in terms of dose and drug form used.
All measurements done by a single person to avoid interobserver variations.
Limitations of Our Study
Only patients undergoing HRT in suppressed cycle were taken with exclusion of natural, modified natural and direct cycles.
Limited sample size.
3D vascularity parameters are better correlated with pregnancy outcomes when compared to 2D and can be a novel method to assess endometrial receptivity. We would like to use the cut-off values obtained from this study and analyze if that helps in decision-making regarding embryo transfer.
Rashmi Vohra https://orcid.org/0000-0001-9129-2261
1. CDC. American Society for Reproductive Medicine; Society for Assisted Reproductive Technology. 2016 assisted reproductive technology national summary report. Atlanta, GA: US Department of Health and Human Services, CDC. (2018).
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3. Jinno M, Ozaki T, Iwashita M, et al. Measurement of endometrial tissue blood flow: a novel way to assess uterine receptivity for implantation. Fertil Steril 2001;76(6):1168-1174. DOI: 10.1016/s0015-0282(01)02897-7
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6. Ng EH, Chan CC, Tang OS, et al. The role of endometrial and subendometrial vascularity measured by three-dimensional power doppler ultrasound in the prediction of pregnancy during frozen-thawed embryo transfer cycles. Hum Reprod 2006;21(6):1612-1617. DOI: 10.1093/humrep/dei502
7. Maugey-Laulom B, Commenges-Ducos M, Jullien V, et al. Endometrial vascularity and ongoing pregnancy after IVF. Eur J Obstet Gynecol Reprod Biol 2002;104(2):137-143. DOI: 10.1016/s0301-2115(02)00102-1
8. Kim A, Jung H, Choi WJ, et al. Detection of endometrial and subendometrial vasculature on the day of embryo transfer and prediction of pregnancy during fresh in vitro fertilization cycles. Taiwan J Obstet Gynecol 2014;53(3):360-365. DOI: 10.1016/j.tjog.2013.05.007
9. Mishra VV, Agarwal R, Sharma U, et al. Endometrial and subendometrial vascularity by three-dimensional (3D) power doppler and Its correlation with pregnancy outcome in frozen embryo transfer (FET) Cycles. J Obstet Gynaecol India 2016;661:521-527. DOI: 10.1007/s13224-016-0871-5
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