Definition and sonographic reporting system for Cesarean scar pregnancy in early gestation: modified Delphi method

Abstract

Objective: To develop a standardized sonographic evaluation and reporting system for Cesarean scar pregnancy (CSP) in the first trimester, for use by both general gynecology and expert clinics.

Methods: A modified Delphi procedure was carried out, in which 28 international experts in obstetric and gynecological ultrasonography were invited to participate. Extensive experience in the use of ultrasound to evaluate Cesarean section (CS) scars in early pregnancy and/or publications concerning CSP or niche evaluation was required to participate. Relevant items for the detection and evaluation of CSP were determined based on the results of a literature search. Consensus was predefined as a level of agreement of at least 70% for each item, and a minimum of three Delphi rounds were planned (two online questionnaires and one group meeting).

Results: Sixteen experts participated in the Delphi study and four Delphi rounds were performed. In total, 58 items were determined to be relevant. We differentiated between basic measurements to be performed in general practice and advanced measurements for expert centers or for research purposes. The panel also formulated advice on indications for referral to an expert clinic. Consensus was reached for all 58 items on the definition, terminology, relevant items for evaluation and reporting of CSP. It was recommended that the first CS scar evaluation to determine the location of the pregnancy should be performed at 6-7 weeks' gestation using transvaginal ultrasound. The use of magnetic resonance imaging was not considered to add value in the diagnosis of CSP. A CSP was defined as a pregnancy with implantation in, or in close contact with, the niche. The experts agreed that a CSP can occur only when a niche is present and not in relation to a healed CS scar. Relevant sonographic items to record included gestational sac (GS) size, vascularity, location in relation to the uterine vessels, thickness of the residual myometrium and location of the pregnancy in relation to the uterine cavity and serosa. According to its location, a CSP can be classified as: (1) CSP in which the largest part of the GS protrudes towards the uterine cavity; (2) CSP in which the largest part of the GS is embedded in the myometrium but does not cross the serosal contour; and (3) CSP in which the GS is partially located beyond the outer contour of the cervix or uterus. The type of CSP may change with advancing gestation. Future studies are needed to validate this reporting system and the value of the different CSP types.

Conclusion: Consensus was achieved among experts regarding the sonographic evaluation and reporting of CSP in the first trimester. © 2021 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Keywords: Cesarean scar pregnancy; Delphi technique; cicatrix; classification; pregnancy; ultrasonography.

© 2021 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Figures

Figure 1

Study design: stepwise modified Delphi method used to reach consensus on the definition of Cesarean scar pregnancy and sonographic evaluation of the uterine scar in the first trimester of pregnancy.

Figure 2

Flow diagram summarizing agreement with or rejection of items during Delphi procedure. Items were accepted if consensus agreement of at least 70% was reached.

Figure 3

A pregnancy located near the Cesarean scar/niche without being in direct contact with it should be called ‘low‐implanted pregnancy’. ‘Distance A’ is the distance between the proximal border of the niche and the most distal border of the gestational sac.

Figure 4

Differentiation of Cesarean scar pregnancy according to position of the gestational sac in relation to two imaginary lines: the ‘uterine cavity line’, i.e. the imaginary line at the transition of the endometrium and myometrium, and the ‘serosal line’, i.e. the imaginary line at the outer border of the myometrium.

Figure 5

Schematic (a,c,e) and ultrasound (b,d,f) images, showing differentiation of Cesarean scar pregnancy (CSP) according to position of the gestational sac (GS) in relation to the uterine cavity line and the serosal line. (a,b) CSP with the largest part of the GS crossing the uterine cavity line. (c,d) CSP with the largest part of the GS embedded in the myometrium and not crossing the uterine cavity line, and the GS not crossing the serosal line. (e,f) CSP crossing the serosal line.

Figure 6

Measurement of residual myometrial thickness (RMT) and adjacent myometrial thickness (AMT) in the sagittal plane in cases of a niche in the non‐pregnant state. Adapted with permission from Jordans et al..

Figure 7

Schematic (a,c,e,g) and ultrasound (b,d,f,h) images showing assessment of location of Cesarean scar pregnancy (CSP) in relation to the uterine arteries in the transverse plane. (a,b) Median location of CSP. (c,d) Eccentric location of CSP; the gestational sac (GS) is connected with the cervical canal and is within the outer cervical contour. (e,f) Lateral location of CSP; the GS protrudes towards the broad ligament within the virtual outer cervical contour and the residual myometrium is visible (CSP with largest part of GS embedded in the myometrium and not crossing the serosal line). (g,h) Lateral location of CSP; the GS is bulging beyond the outer cervical contour and residual myometrium is absent (CSP crossing the serosal line). RMT, residual myometrial thickness.

Figure 8

Flowchart showing evaluation of the Cesarean section (CS) scar in first trimester of pregnancy. Step 1: determination of location of the pregnancy: intrauterine pregnancy, low‐implanted pregnancy, Cesarean scar pregnancy (CSP) or miscarriage. Step 2: determination of type of CSP depending on whether the largest part of the gestational sac (GS) is crossing the uterine cavity line (UCL): (a) if the largest part of the GS is crossing the UCL, it should be determined whether the location of the largest part of the GS is in the uterine cavity or in the cervical canal; (b) if the largest part of the GS is not crossing the UCL, the existence of bulging should be determined: (i) if there is no bulging, i.e. the pregnancy is located completely within the level of the serosa/serosal line (SL), it is a CSP with the largest part of the GS in the myometrium and not crossing the SL; (ii) if there is bulging, i.e. the pregnancy is located partly beyond the contour of the outer cervix/SL, it is a CSP crossing the SL. Step 3: determination of location of the placenta: in the niche, near the niche or placenta previa. Step 4: evaluation of presence of signs of abnormally adherent placenta: yes or no? *Management regarding follow‐up or treatment will depend on patient characteristics and wishes. †To be evaluated in future cases and validated by peer‐reviewed articles.