Early first-trimester transvaginal ultrasound screening for cesarean scar pregnancy in patients with previous cesarean delivery: analysis of the evidence.

Obstetric hemorrhage is a leading cause of maternal morbidity and mortality. An important etiology of obstetric hemorrhage is placenta accreta spectrum. In the last 2 decades, there has been increased clinical experience of the devastating effect of undiagnosed, as well as late diagnosed, cases of cesarean scar pregnancy. There is a growing body of evidence suggesting that cesarean scar pregnancy is an early precursor of second- and third-trimester placenta accreta spectrum. As such, cesarean scar pregnancy should be diagnosed in the early first trimester. This early diagnosis could be achieved by introducing regimented sonographic screening in pregnancies of patients with previous cesarean delivery. This opinion article evaluates the scientific and clinical basis of whether cesarean scar pregnancy, with special focus on its early first-trimester discovery, complies with the accepted requirements of a screening test. Each of the 10 classical screening criteria of Wilson and Jungner were systematically applied to evaluate if the criteria were met by cesarean scar pregnancy, to analyze if it is possible and realistic to carry out screening in a population-wide fashion.

The effect of uterine closure technique on cesarean scar niche development after multiple cesarean deliveries.

OBJECTIVES: To use saline infusion sonohysterography (SIS) to evaluate the effect of uterine closure technique on niche formation after multiple cesarean deliveries (CDs). METHODS: Patients with at least one prior CD were evaluated for niche via SIS. Subgroups of any number repeat CD (>1 prior), lower-order CD (<4 prior), and higher-order CD (≥4 prior) were analyzed, stratifying by hysterotomy closure technique at last cesarean preceding imaging; techniques included Technique A (endometrium-free double-layer closure) and Technique B (single- or double-layer routine endo-myometrial closure). Niche defects were quantified (depth, length, width, and residual myometrial thickness). The primary outcome was clinically significant niche, defined as depth >2 mm. Statistical analysis was performed using chi-square, ANOVA, t-test, Kruskal-Wallis, and multiple logistic regression, with p-values of <0.05 were statistically significant. RESULTS: A total of 172 post-cesarean SIS studies were reviewed: 105 after repeat CDs, 131 after lower-order CDs, and 41 after higher-order CDs. Technique A was associated with a shorter interval to imaging and more double-layer closures. Technique B was associated with more clinically significant niches across all subgroups, and these niches were significantly longer and deeper when present. Multiple logistic regression demonstrated a 5.6, 8.1, and 11-fold increased adjusted odds of clinically significant niche following Technique B closure in the repeat CD (p<0.01), lower-order CD (p<0.001), and higher-order CD (p=0.04) groups, respectively. CONCLUSIONS: While multiple CDs are known to increase risk for niche defects and their sequelae, hysterotomy closure technique may help to reduce niche development and severity.

The Impact of Uterine Incision Closure Techniques on Post-cesarean Delivery Niche Formation and Size: Sonohysterographic Examination of Nonpregnant Women.

OBJECTIVE: To compare the prevalence and size of residual niche in the nongravid uterus following Cesarean delivery (CD) with different hysterotomy closure techniques (HCTs). METHODS: Saline infusion sonohysterogram (SIS) was performed in women after one prior CD, documenting the presence or absence of a postoperative niche and measuring its depth, width, length, and residual myometrial thickness. Women were grouped by HCT: Technique A (endometrium-free) and Technique B (routine non-endometrium-free). The primary outcome was the prevalence of a clinically significant niche, defined as a depth of >2 mm. HCT groups were compared using χ2 , T-test (ANOVA), and analyzed using logistic regression and two-sided test (P < .05). RESULTS: Forty-five women had SIS performed, 25 and 20 via Technique A and B, respectively. Technique groups varied by average interval time from CD to SIS (13.6 versus 74.5 months, P = 0.006) but were otherwise similar. Twenty niches were diagnosed, 85% of which were clinically significant, including five following Technique A, nine following Technique B with double-layer closure, and three following Technique B with single-layer (P = .018). The average niche depth was 2.4 mm and 4.9 mm among the two-layer subgroups following Techniques A and B, respectively (P = .005). A clinically significant niche development was six times higher with Technique B when compared to Technique A (OR 6.0, 95% CI 1.6-22.6, P = .008); this significance persisted after controlling for SIS interval on multivariate analysis (OR 4.4, 95% CI 1.1-18.3, P = .04). The average niche depth was 5.7 ± 2.9 mm following Technique B with single-layer. CONCLUSION: Hysterotomy closure techniques determine the prevalence of post-Cesarean delivery niche formation and size. Exclusion of the endometrium at uterine closure reduces the development of significant scar defects.

Methodological Quality of Fetal Brain Structure Charts for Screening Examination and Targeted Neurosonography: A Systematic Review.

INTRODUCTION: Several fetal brain charts have been published in the literature and are commonly used in the daily clinical practice. However, the methodological quality of these charts has not been critically appraised. MATERIAL AND METHODS: MEDLINE, EMBASE, CINAHL, and the Web of Science databases were searched electronically up to December 31, 2020. The primary outcome was to evaluate the methodology of the studies assessing the growth of fetal brain structures throughout gestation. A list of 28 methodological quality criteria divided into three domains according to "study design," "statistical and reporting methods," and "specific relevant neurosonography aspects" was developed in order to assess the methodological appropriateness of the included studies. The overall quality score was defined as the sum of low risk of bias marks, with the range of possible scores being 0-28. This quality assessment was applied to each individual study reporting reference ranges for fetal brain structures. Furthermore, we performed a subgroup analysis according to the different brain structures (ventricular and periventricular, fore-brain and midbrain cerebral and posterior fossa). RESULTS: Sixty studies were included in the systematic review. The overall mean quality score of the studies included in this review was 51.3%. When focusing on each of the assessed domains, the mean quality score was 53.7% for "study design," 54.2% for "statistical and reporting methods," and 38.6% for "specific relevant neurosonography aspects." The sample size calculation, the correlation with a postnatal imaging evaluation, and the whole fetal brain assessment were the items at the highest risk of bias for each domain assessed, respectively. The subgroup analysis according to different anatomical location showed the lowest quality score for ventricular and periventricular structures and the highest for cortical structures. CONCLUSIONS: Most previously published studies reporting fetal brain charts suffer from poor methodology and are at high risk of biases, mostly when focusing on neurosonography issues. Further prospective longitudinal studies aiming at constructing specific growth charts for fetal brain structures should follow rigorous methodology to minimize the risk of biases, guarantee higher levels of reproducibility, and improve the standard of care.

Placenta accreta spectrum disorders in the first trimester: a systematic review.

Placenta accreta spectrum (PAS) disorders involve an abnormality in the implantation of the placenta, being rarely diagnosed in the first trimester. To conduct a systematic review of the risk factors, clinical and imaging features, and outcomes of histopathologically confirmed cases of PAS disorders in the first trimester of pregnancy. Different databases including PubMed, MEDLINE Complete, Scopus, Web of Science, EMBASE, SciELO, LILACS, and Ovid were reviewed up to November 2018. 55 patients with a definitive histopathological diagnosis were reported. About 18 had a history of prior curettage and 47 of previous caesarean deliveries (CD). About 74.54% presented with miscarriage and ultrasound signs of caesarean scar pregnancy (CSP) were reported in 22.49%. Temporal sequence of diagnostic studies could be determined in 52 women, and, among these, PAS disorders were defined through imaging techniques in 11 (21.15%) while surgical findings unveiled them in 15 (28.84%). Nonetheless, in half of the cases, the diagnosis was concluded only on histopathological samples. PAS disorders in the first trimester of pregnancy are rarely diagnosed through imaging techniques and lead to hysterectomy in most cases. Ultrasound training to detect PAS disorders in women with risk factors is crucial for early diagnosis and prevention of adverse outcomes.

Special Report of the Society for Maternal-Fetal Medicine Placenta Accreta Spectrum Ultrasound Marker Task Force: Consensus on definition of markers and approach to the ultrasound examination in pregnancies at risk for placenta accreta spectrum.

Placenta accreta spectrum includes the full range of abnormal placental attachment to the uterus or other structures, encompassing placenta accreta, placenta increta, placenta percreta, morbidly adherent placenta, and invasive placentation. The incidence of placenta accreta spectrum has increased in recent years, largely driven by increasing rates of cesarean delivery. Prenatal detection of placenta accreta spectrum is primarily made by ultrasound and is important to reduce maternal morbidity associated with the condition. Despite a large body of research on various placenta accreta spectrum ultrasound markers and their screening performance, inconsistencies in the literature persist. In response to the need for standardizing the definitions of placenta accreta spectrum markers and the approach to the ultrasound examination, the Society for Maternal-Fetal Medicine convened a task force with representatives from the American Institute of Ultrasound in Medicine, the American College of Obstetricians and Gynecologists, the American College of Radiology, the International Society of Ultrasound in Obstetrics and Gynecology, the Society for Radiologists in Ultrasound, the American Registry for Diagnostic Medical Sonography, and the Gottesfeld-Hohler Memorial Ultrasound Foundation. The goals of the task force were to assess placenta accreta spectrum sonographic markers on the basis of available data and expert consensus, provide a standardized approach to the prenatal ultrasound evaluation of the uterus and placenta in pregnancies at risk of placenta accreta spectrum, and identify research gaps in the field. This manuscript provides information on the Placenta Accreta Spectrum Task Force process and findings.

Three-Dimensional Coronal Plane of the Uterus: A Critical View for Diagnostic Accuracy.

Two-dimensional transvaginal and transabdominal ultrasound (US) examinations are the suggested methods for examining the uterus. Three-dimensional (3D) US, which is not compulsory by society guidelines, provides additional uterine views, reassuring users of pathologic conditions not evident on customary sagittal and transverse views. The 3D coronal plane is rarely seen by 2-dimensional US transducers, let alone in extremely retroverted or axial uteri. Ultrasound machines nowadays feature 3D US capability. Our experience is that the coronal uterine view is a problem solver, helping diagnostic abilities of pelvic imaging. We advocate its liberal use and its acquisition in every pelvic scan. In this Pictorial Essay we present examples to demonstrate its use.

Society for Maternal-Fetal Medicine (SMFM) Consult Series #49: Cesarean scar pregnancy.

Cesarean scar pregnancy is a complication in which an early pregnancy implants in the scar from a prior cesarean delivery. This condition presents a substantial risk for severe maternal morbidity because of challenges in securing a prompt diagnosis, as well as uncertainty regarding optimal treatment once identified. Ultrasound is the primary imaging modality for cesarean scar pregnancy diagnosis, although a correct and timely determination can be difficult. Surgical, medical, and minimally invasive therapies have been described for cesarean scar pregnancy management, but the optimal treatment is not known. Women who decline treatment of a cesarean scar pregnancy should be counseled regarding the risk for severe morbidity. The following are Society for Maternal-Fetal Medicine recommendations: We recommend against expectant management of cesarean scar pregnancy (GRADE 1B); we suggest operative resection (with transvaginal or laparoscopic approaches when possible) or ultrasound-guided vacuum aspiration be considered for surgical management of cesarean scar pregnancy and that sharp curettage alone be avoided (GRADE 2C); we suggest intragestational methotrexate for medical treatment of cesarean scar pregnancy, with or without other treatment modalities (GRADE 2C); we recommend that systemic methotrexate alone not be used to treat cesarean scar pregnancy (GRADE 1C); in women who choose expectant management and continuation of a cesarean scar pregnancy, we recommend repeat cesarean delivery between 34 0/7 and 35 6/7 weeks of gestation (GRADE 1C); we recommend that women with a cesarean scar pregnancy be advised of the risks of another pregnancy and counseled regarding effective contraceptive methods, including long-acting reversible contraception and permanent contraception (GRADE 1C).

Ultrasound and Histopathologic Correlation of Ovarian Cystadenofibromas: Diagnostic Value of the "Shadow Sign".

OBJECTIVES: Cystadenofibromas (CAFs) are rare benign ovarian tumors without a widely accepted ultrasound (US) pattern. They are usually described by as thin-walled, unilocular or multilocular, and at times septated cysts with scant blood flow and no solid components. We describe a unique US feature, the "shadow sign," seen in prospectively diagnosed benign CAFs. We also provide the histopathologic basis for this typical US appearance. METHODS: Ultrasound (US) examinations were performed in our obstetric and gynecologic US unit. Pathologic examinations were performed by a dedicated gynecologic pathology team. The US and pathology department's database was searched for the diagnosis of a CAF between 2010 and 2017. RESULTS: We identified 20 patients who underwent transvaginal US examinations with a sole US diagnosis of a CAF, and the tumors were surgically removed. The common US feature across the 20 cases was the presence of hyperechoic avascular shadowing nodules. The correlating histologic features were unilocular or multilocular cysts with a smooth internal wall surface lined by a simple epithelium and occasional robust polypoid fibrous stroma. CONCLUSIONS: This US marker helps in differentiating CAFs from borderline ovarian tumors, which do not show this US feature. We hope that recognizing the suggested shadow sign as an additional descriptor of CAFs will lead to minimizing their unnecessary removal and eliminating additional and unnecessary imaging by computed tomography and magnetic resonance imaging.

Minimally Invasive Treatment of Cesarean Scar and Cervical Pregnancies Using a Cervical Ripening Double Balloon Catheter: Expanding the Clinical Series.

The efficacy of treating cesarean scar pregnancies and cervical pregnancies with the Cook® cervical ripening balloon catheter, in a multicenter office-based setting is reported. Thirty-eight women were treated. Insertion of the catheter was performed under real-time ultrasound guidance. Patients received adjuvant systemic methotrexate, prophylactic oral antibiotics, and oral pain medication. Serum human chorionic gonadotropin and ultrasound scans were followed serially until resolution. Thirty-seven patients were successfully treated, requiring no further procedures. We found that the Cook cervical ripening balloon technique is a simple, effective, outpatient, minimally invasive treatment with few complications noted in this expanded series.

Cesarean Delivery Changes the Natural Position of the Uterus on Transvaginal Ultrasonography.

OBJECTIVES: To assess whether cesarean delivery changes the natural position of the uterus. METHODS: In this retrospective Institutional Review Board-approved cohort study, we conducted a search of our university gynecologic ultrasonography (US) database. Patients with transvaginal US images before and after either vaginal or cesarean delivery between 2012 and 2015 were included. Women with prior cesarean delivery were excluded. Two readers independently measured antepartum and postpartum flexion angles between the longitudinal axis of the uterine body and the cervix. We calculated intraclass correlation coefficients to measure inter-reader agreement. Antepartum and postpartum uterine flexion angles were compared between patients with vaginal and cesarean delivery. RESULTS: We included 173 patients (107 vaginal and 66 cesarean delivery). The mean interval between scans ± SD was 18 ± 10 months. Inter-reader agreement for flexion angles was almost perfect (intraclass correlation coefficients: antepartum, 0.939; postpartum, 0.969; both P < .001). There was no difference in mean antepartum flexion angles for cesarean delivery (154.8° ± 45.7°) versus vaginal delivery (145.8° ± 43.7°; P = .216). Mean postpartum flexion angles were higher after cesarean delivery (180.4° ± 51.2°) versus vaginal delivery (152.8° ± 47.7°; P = .001. Differences in antepartum and postpartum flexion angles between cesarean and vaginal delivery were statistically significant (25.6° versus 7.0°; P = .027). CONCLUSIONS: Cesarean delivery can change the uterine flexion angle to a more retroflexed position. Therefore, all women with a history of cesarean delivery should undergo a transvaginal US examination before any gynecologic surgery or intrauterine device placement to reduce the possibility of surgical complications.

Pregnancy in an Abnormal Location.

Cesarean scar pregnancy and cervical pregnancy are 2 relatively rare types of abnormally implanted pregnancies. Both if unrecognized can result in significant morbidity to the patient. The most important issue regarding cesarean scar pregnancy and cervical pregnancy is to establish the diagnosis early in order for the patient to be adequately counseled and appropriate management carried out. For both of these conditions early detection and treatment can result in preservation of fertility.

Tubal Disease and Impersonators/Masqueraders.

Ultrasound is considered the first-line imaging modality in the evaluation of the fallopian tubes. This chapter reviews both the physiologic and pathologic sonographic findings of the fallopian tubes and how to recognize characteristic entities. Specifically, it describes how to use ultrasound techniques to distinguish between pathologic processes including chronic versus acute pelvic inflammatory disease, as well as infertility, torsion, and malignancy. It also describes how to employ modern ultrasound techniques, such as color Doppler, three-dimensional imaging, and salpingocentesis in clinical practice.

Ultrasound Detection of Bladder-Uterovaginal Anastomoses in Morbidly Adherent Placenta.

Vascular control is a fundamental step in the surgical management of morbidly adherent placenta (MAP), and this implies a precise knowledge of the vascular supply in the lower part of the genital tract. High degrees of MAP are sometimes characterised by the presence of a rich vascular anastomotic system between the bladder, uterus, and vagina involving the superior, medial, and inferior vaginal and the lower vesical arteries. This brief report shows that prenatal ultrasound assessment of bladder-uterovaginal anastomoses in MAP is feasible.

Ultrasound diagnosis and management of acquired uterine enhanced myometrial vascularity/arteriovenous malformations.

BACKGROUND: Arteriovenous malformation is a short circuit between an organ's arterial and venous circulation. Arteriovenous malformations are classified as congenital and acquired. In the uterus, they may appear after curettage, cesarean delivery, and myomectomy among others. Their clinical feature is usually vaginal bleeding, which may be severe, if curettage is performed in unrecognized cases. Sonographically on 2-dimensional grayscale ultrasound scanning, the pathologic evidence appears as irregular, anechoic, tortuous, tubular structures that show evidence of increased vascularity when color Doppler is applied. Most of the time they resolve spontaneously; however, if left untreated, they may require involved treatments such as uterine artery embolization or hysterectomy. In the past, uterine artery angiography was the gold standard for the diagnosis; however, ultrasound scanning has diagnosed successfully and helped in the clinical management. Recently, arteriovenous malformations have been referred to as enhanced myometrial vascularities. OBJECTIVES: The purpose of this study was to evaluate the role of transvaginal ultrasound scanning in the diagnosis and treatment of acquired enhanced myometrial vascularity/arteriovenous malformations to outline the natural history of conservatively followed vs treated lesions. METHODS: This was a retrospective study to assess the presentation, treatment, and clinical pictures of patients with uterine Enhanced myometrial vascularity/arteriovenous malformations that were diagnosed with transvaginal ultrasound scanning. We reviewed both (1) ultrasound data (images, measured dimensions, and Doppler blood flow that were defined by its peak systolic velocity and (2) clinical data (age, reproductive status, clinical presentation, inciting event or procedure, surgical history, clinical course, time intervals that included detection to resolution or detection to treatment, and treatment rendered). The diagnostic criteria were "subjective" with a rich vascular network in the myometrium with the use of color Doppler images and "objective" with a high peak systolic velocity of ≥20 cm/sec in the vascular web. Statistical analysis was performed and coded with statistical software where necessary. RESULTS: Twenty-seven patients met the diagnostic criteria of uterine enhanced myometrial vascularity/arteriovenous malformation. Mean age was 31.8 years (range, 18-42 years). Clinical diagnoses of the patients included 10 incomplete abortions, 6 missed abortions, 5 spontaneous complete abortions, 5 cesarean scar pregnancies, and 1 molar pregnancy. Eighty-nine percent of patients had bleeding (n = 24/27), although 1 patient was febrile, and 2 patients were asymptomatic. Recent surgical procedures were performed in 55.5% patients (15/27) that included curettage (n = 10), cesarean deliveries (n = 5), or both (n = 1); 4 patients had a remote history of uterine surgery that included myomectomy. Treatment was varied and included expectant treatment alone in 48% of the patients with serial ultrasound scans and serum human chorionic gonadotropin until resolution (n = 13/27 patients), uterine artery embolization (29.6%; 8/27 patients), methotrexate administration (22.2%; 6/27 patients), hysterectomy (7.4%; 2/27 patients), and curettage (3.7%; 1/27 patients). Three patients required a blood transfusion. Of the 9 patients whose condition required embolization, the conditions of 7 patients resolved after the procedure although 1 patient's condition required operative hysteroscopy and 1 patient's condition required hysterectomy for intractable bleeding. Average peak systolic velocity after embolization in the 9 patients was 85.2 cm/sec (range, 35-170 cm/sec); the average peak systolic velocity of the 16 patients with spontaneous resolution was 58.5 cm/sec (range, 23-90 cm/sec). CONCLUSIONS: Acquired enhanced myometrial vascularity/arteriovenous malformations occurred after unsuccessful pregnancies or treatment procedures that included uterine curettage, cesarean delivery, or cesarean scar pregnancy. Triage of patients for expectant treatment vs intervention with uterine artery embolization based on their clinical status, which was supplemented by objective measurements of blood velocity measurement in the arteriovenous malformation, appears to be a good predictor of outcome. Ultrasound evaluation of patients with early pregnancy failure and persistent bleeding should be considered for evaluation of a possible enhanced myometrial vascularity/arteriovenous malformation.

A new minimally invasive treatment for cesarean scar pregnancy and cervical pregnancy.

BACKGROUND: Cesarean scar pregnancy and cervical pregnancy are unrelated forms of pathological pregnancies carrying significant diagnostic and treatment challenges, with a wide range of treatment effectiveness and complication rates ranging from 10% to 62%. At times, life-saving hysterectomy and uterine artery embolization are required to treat complications. Based on our previous success with using a single-balloon catheter for the treatment of cesarean scar pregnancy after local injection of methotrexate, we evaluated the use of a double-balloon catheter to terminate the pregnancy while preventing bleeding without any additive treatment. This was a retrospective study. OBJECTIVES: The objective of the study was to describe the placement of a cervical ripening double-balloon catheter as a novel, minimally invasive treatment in patients with cesarean scar and cervical pregnancies to terminate the pregnancy and at the same time prevent bleeding by compressing the blood supply of the gestational sac. STUDY DESIGN: Patients with diagnosed, live cervical pregnancy and cesarean scar pregnancy between 6 and 8 weeks' gestation were considered for the office-based treatment. Paracervical block with 1% lidocaine was administered in 3 patients for pain control. Insertion of the catheter and inflation of the upper balloon were done under transabdominal ultrasound guidance. The lower (pressure) balloon was inflated opposite the gestational sac under transvaginal ultrasound guidance. After an hour, the area of the sac was scanned. When fetal cardiac activity was absent and no bleeding was noted, patients were discharged. After 2-3 days, a follow-up appointment was scheduled for possible catheter removal. Serial ultrasound (US) and serum human chorionic gonadotropin were followed weekly or as needed. RESULTS: Three live cervical pregnancies and 7 live cesarean scar pregnancies were successfully treated. Median gestational age at treatment was 6 6/7 weeks (range 6 1/7 through 7 4/7 weeks). Patients' acceptance for the double-balloon treatment was high in spite of the initial low abdominal pressure felt at the inflation of the balloons. All but 1 patient noted vaginal spotting at the follow-up appointment. Only 1 patient experienced bleeding of dark blood. The balloons were in place for a median of 3 days (range, 1-5 days). Median time from treatment to the total drop of human chorionic gonadotropin was 49 days (range, 28-97 days). CONCLUSION: The double balloon is a successful, minimally invasive and well-tolerated single treatment for cervical pregnancy and cesarean scar pregnancy. This simple treatment method has 4 main advantages: it effectively stops embryonic cardiac activity, prevents bleeding complications, does not require any additional invasive therapies, and is familiar to obstetricians-gynecologists who use the same cervical ripening catheters for labor induction. Its wider application, however, has to be validated on a larger patient population.

Easy sonographic differential diagnosis between intrauterine pregnancy and cesarean delivery scar pregnancy in the early first trimester.

BACKGROUND: Cesarean scar pregnancy (CSP) is a serious complication of pregnancy, which consists of implantation of the gestational sac in the hysterotomy scar. This condition is increasing in frequency and often poses a diagnostic challenge. Its diagnosis is dependent on visual assessment of the uterus on the longitudinal sagittal ultrasound plane. Misdiagnosing a low intrauterine chorionic sac as a CSP, or a true scar pregnancy as an intrauterine pregnancy (IUP), may lead to adverse outcomes including hysterectomy. OBJECTIVE: The objective of the study is to describe a sonographic method for the differential diagnosis of CSP vs IUP in early gestation. The current study tests the hypothesis that on a first-trimester ultrasound performed between 5-10 weeks of gestation, the relative location of the center of gestational sac to the midpoint of the uterus along a longitudinal line between the external cervical os and the fundus can be used for early detection of CSPs. STUDY DESIGN: This is a retrospective review of electronically archived ultrasound images of IUP and CSP between 5-10 weeks of gestation. A total of 242 ultrasound images were analyzed: 185 cases of normal IUPs (including 128 in anteverted uteri, 31 in retroverted uteri, and 26 IUPs with history of cesarean delivery) and 57 cases of CSPs diagnosed from 2004 through 2015 in a single institution. The following measurements were made for each case: distance from the external cervical os to the uterine fundus, the midpoint axis of the uterus, the distance from the external cervical os to the center of gestational sacs, and the distance from the external cervical os to the most distant edge of the gestational sacs from the cervix. RESULTS: The location of the center of the gestational sac relative to the midpoint axis of the uterus between 5-10 weeks of gestation differentiated between IUP and CSP (mean 17.8 vs -10.6 mm, respectively, P = .0001), indicating that most CSPs are located proximally to the midpoint axis of the uterus whereas most normal IUPs are located distally from the midpoint of the uterus. Using location of the center of the gestational sac as a marker of CSPs between 5-10 weeks of gestation yielded the following characteristics of diagnostic accuracy: sensitivity 93.0% and specificity 98.9%. The likelihood ratio of the positive test was 84.5. The likelihood ratio of the negative test was 0.07. CONCLUSION: The location of the center of the gestational sac relative to the midpoint axis of the uterus can be used as an easy method for sonographic differentiation of IUP and CSP between 5-10 weeks of gestation.