Niche pregnancy and niche measurement in pregnancy

Round 2 Questionnaire – Expert Opinion

Thank you very much for your input in the Round 1 questionnaire.

Consensus was predefined as 70%, this implies agreement of 11 out of 15 experts. Of all 103 questions asked (including sub-questions), consensus was reached for 50 questions (49%). We will send you an overview separately.

Introduction to the second questionnaire of the Delphi procedure
In the first questionnaire consensus was reached on the exact measurements of a niche in the first trimester; this was agreed to be similar to the method described in the first Delphi procedure of niche measurement in non-pregnant women. However, no full consensus was reached on definitions and differentiation between several pregnancy locations.

In this second questionnaire we will introduce a new classification of a cesarean scar pregnancy (CSP), which will be elaborated below. Using this classification various questions about definitions and differentiation became irrelevant and we were able to shorten the current questionnaire. But relevant questions without consensus concerning ultrasound features in the first trimester, placentation, follow-up (basic vs advanced evaluation) and additional methods (Doppler ultrasound, MRI) will be repeated. The item “treatment” is added to the questionnaire.

This questionnaire contains 36 questions and will probably take less time (30 minutes) than the first.

The final goal of this Delphi procedure is to develop a e-learning program which can be used by all gynecologists, residents and ultra sonographers. Some questions in this second questionnaire will refer to this final achievement, i.e. tips and tricks that can be useful in the e-learning.

NEW PROPOSAL CSP CLASSIFICATION
Based on the answers we identified two terms that were differently used by different experts; the caesarean scar pregnancy (CSP) and niche pregnancy (NP). Some of you call a CSP a pregnancy in the niche and others also include pregnancies on the CS scar or near the CS scar. Differences in definitions is not only a problem during this Delphi procedure but is also observed in current literature. It is important that we all use the same uniform terms. It also became clear that it is important for eventual treatment options to differentiate between a pregnancy on the CS scar and in the CS scar. Therefore we propose the following terminology that we formulated on suggestions of some experts and in line with the ESGE and FIGO classification of submucous fibroids. The latter will improve implementation in daily practise.

We propose to use CSP as a collective term that includes all pregnancies (gestational sac and/or placenta) near/on/in the caesarean scar and can be subdivided in a type 1 CSP and a type 2 CSP, as illustrated below:

1. A type 1 CSP could be defined as a gestational sac that is located >50% in the cervix/uterine cavity and ≤50% in the myometrium/niche.
2. A type 2 CSP (or niche pregnancy) could be defined as a pregnancy that is located ≤50% in the cervix or uterine cavity and thus > 50% located in the niche/myometrium.

Type 1 CSP: ≥50% of sac is located outside the level of the myometrium/niche and is located in the cervical channel/uterine cavity.


Type 2 CSP: ≤50% of the sac is located outside the level of the myometrium/niche and more than 50% is located in the cervical channel/outside uterine cavity. This may also called a pregnancy IN the niche or a niche pregnancy.


The flow chart below presents the different situations that can be encountered while performing an ultrasound early in pregnancy after previous CS. A pregnancy can be located intra-uterine or low in cavity/ cervical channel (which can be difficult to distinguish). If located low in cavity/ cervical channel there can be a type 1 CSP, type 2 CSP or a miscarriage. Note that it may change in time and that a CSP type 1 according to the new classification only describes a situation and it does not necessarily mean that it needs to be treated.
Click on the image to enlarge.
We propose to examine the following items in 5 steps:

• If type 1: determination of the location of largest part of the GS; in uterine cavity or in the cervical canal
• If type 2: determination of the existence of bulging:
  • If no bulging, i.e. the pregnancy is located completely within the level of the serosa/outer cervical contour, it is called a type 2A
  • If bulging, i.e the pregnancy is partly located outside the contour of the outer cervix/uterine line, it is called a type 2B

• Step 4: Location of the placenta; in niche / near niche / placenta praevia?
• Step 5: Sign of abnormal adherent placenta; yes or no?

Note that the differentiation between the various types including differentiation between type 2A and type 2B may be of influence on the treatment options and for eventual referral to an expert center.

For example it could be considered to treat type 2A with curettage (after cerclage/with balloon) and that type 2B requires other approaches (for example laparoscopic niche resection). So we think it may be important to differentiate between these different types but we will discuss their effect on therapeutic policies in the next round. First we need to talk the same language and that is the purpose of the current Delphi round.

1. Definitions

CSP

Type 1 CSP

Type 2 CSP

2. Differentiate between various CSP and miscarriage

Intra-uterine pregnancy vs type 1 CSP

The following items were considered relevant for a CSP:

• The gestational sac is implanted at the site of the previous uterine caesarean scar
• Minimal distance of the gestational sac to the niche
• An empty uterine cavity
• The presence of a rich vascular pattern in the area of the uterine caesarean scar and the placenta on Doppler ultrasound evaluation to differentiate from an (ongoing) miscarriage.

We would like to specify the location of the gestational sac in case of a type 1 CSP and therefore we also present the results of the previous methods to measure pregnancy location.
We showed 3 methods to measure and report the pregnancy location. The “subjective-simple” method - subjective evaluation of the location using ultrasound - was found useful (93% of the experts agreed). 60% preferred this method above the 2 others. The “relative” method - using the midline of the uterus length to determine the location -was found useful by 67% of the experts. If one could choose 2 methods, 53% of the experts would choose the subjective simple and relative method over the absolute method – measurement of absolute distances – , so the latter can be skipped.

Probably an easier method to determine the location of the gestational sac is to measure the distance between the proximal part of the niche and the most distal part of the GS, see figure 1. By using this method it would be possible to differentiate between a type 1 CSP (near the CS scar) and a low located (intrauterine) pregnancy.

The caesarean scar may in some cases be located in the uterine corpus instead of the cervix/ lower uterine segment. In case of preterm delivery during the CS the scar may be higher up in the uterine wall. This may complicate the determination of the pregnancy location in subsequent pregnancy. Using the terminology in relation to the CS scar prevents problems with possible high located CS scar and makes it possible to use the classification in all situations.

Note that based on your previous answers it can only be called a CSP if the placenta/infiltration is located at the side of the CS scar and not if it is located on the posterior side, in that case we call it a low located or cervical pregnancy but not a CSP

Type 1 CSP vs type 2 CSP

Bulging of the gestational sac outside the outer-contour of the cervix/uterus towards the bladder was consented to be a relevant ultra sonographic feature since it may determine treatment options. 80% of the experts agreed on this item. We propose to use this item to make a sub classification of type 2 CSP into a type 2A and type 2B.

Differentiation between CSP type 2A and 2B

We propose the following sub classification:
TYPE 2A: the pregnancy/gestational sac is entirely located within the outer contour (blue line) of the cervix/uterus.

TYPE 2B: the pregnancy/gestational sac is partly located outside the outer contour (blue line) of the cervix/uterus.

CSP type 1/2 vs ongoing miscarriage

60% of the experts agreed that the item “sliding product”, which was defined as the inability to displace the gestational sac from its position at the level of the internal os using gentle pressure applied by the transvaginal probe to differentiate from an (ongoing) miscarriage” should be added to the definition of CSP. It can be helpful to distinguish from an ongoing/incomplete miscarriage but several experts indicate that it can be difficult to see this clearly. However if it is sliding it gives an indication that a CSP is less likely.

Few experts suggested to differentiate by the existence of decidual reaction at the implantation site or the trophoblast localisation, in the evaluation of a CSP.

The item “Presence of embryonic/fetal pole and/or yolk sac with or without heart activity” was found relevant to add to the definition of a CSP by 67% of the experts. Explanation of those who agreed:

• It is needed to confirm that is a pregnancy (and not something else, i.e. artefact, nabothian cysts, inclusion cyst)
• If it is a vital pregnancy the risks are increased because of its progress
• It is important for the prognosis and management

argument against including this item:

• Pregnancies without fetal pole are common; those can also be located in a niche.

Based on the above comments we propose to add the presence of a gestational sac to the definition to fetal pole or yolk sac.

3. Ultrasound steps in 1ste trimester

The preferred timeframe to evaluate a niche pregnancy and to discriminate from IUG is 6-7 weeks. However, a type 1 CSP could become a type 2 CSP with advancing gestational age. In early pregnancy it may also be unclear if a pregnancy is type 1 CSP or a cervical pregnancy while with advancing vascularity (gestational age) this may become more evident. In those cases the need for therapy needs to be determined at a later moment.

One of the experts suggested to highlight any cervical pathology if present (i.e. Nabothian cysts in the evaluation of niche pregnancy.

Other suggestions of experts that possibly should be determined or measured during the first trimester ultrasound, after previous CS:

• Distance between external os and the pregnancy (lower part of the sac)
• Cervical length

Please give us your opinion concerning these items.

If relevant or very relevant:

If relevant or very relevant:

4. Intra-uterine pregnancy - placentation

47% of the experts found “Distance between the vessels of the placenta and serosa” relevant in the first trimester evaluation. This item being a first sign of invasion (placenta accreta) was the argument given pro evaluation. It can be relevant for expected problems during therapy / delivery. But it was also questioned whether it is relevant for basic evaluation.

Situation 1

Pregnancy low in the uterine cavity, >50% in uterine cavity and placenta grows into the myometrium, no endometrial lining.
67% defined these situations as a niche pregnancy. However with the pregnancy/gestational sac located >50% in the uterine cavity we propose to consider this a type 1 CSP.

Situation 2

Intra-uterine pregnancy, placenta increta/percreta

67% of the experts found that “lining of the endometrium covering the niche” allows differentiation between niche pregnancy with or without abnormal adherent placenta. They argued that a CSP without lining may indicate an abnormal adherent placenta while clear lining makes an increta less likely. No specific contra arguments were given.

Mostly lining of the endometrium is not clearly visible, but if it is visible an abnormal adherent placenta is less likely at that moment.

67% of the experts found “Presence of placenta praevia” relevant in first trimester evaluation. Arguments given pro evaluation of this item: it is important to determine the risk on a pathologically invasive placenta which can occur in combination with a placenta praevia, especially whether or not it is in or at the caesarean scar. And this feature could be useful in the triage to refer patients to an expert center.

However, it was also mentioned that placenta praevia is a common feature in the first trimester and therefore not always abnormal and not easy to define (high false positive rate).

5. Follow-up / treatment

Possible advantage to differentiate between a CSP type 1 and type 2, type 2a and 2b with our without abnormal adherent placenta is that it may be associated with different treatment options. The exact course of follow-up and when to consider treatment and what type of treatment will be discussed in a later stage. We propose to start a new Delphi procedure to define these items since these may depend on the expertise in a center and this also requires an extensive review of literature first that is currently executed by one of our PhD students.

No consensus was reached on the item “best time frame to assess a niche pregnancy in terms of optimal therapeutic options”. 53% of the experts chose 6-7 weeks; 27% of the experts chose 8-9 weeks. This possibly depends on the type of CSP.

A proposal for evaluation of the pregnancy location in the transversal plane, was shown before in the first questionnaire. In this plane also the location of the pregnancy in relation to the urine arteries was taken into account (visible with colour Doppler). Consensus was reached on the relevance of using colour Doppler in transversal plane and the usefulness of the level of protrusion in relation to the outer serosa contour. The distance between the gestational sac and the uterine arteries was found to have additional value; the location influences the decision for treatment of niche pregnancy. Concerning the relevance of this item (transversal imagine to evaluate the location of a pregnancy) the majority of the experts found it (absolutely) relevant and/or could agree with adding this item.

We assume that the classification of a CSP will mainly be made on the sagittal plane, however in some cases (if the niche is located very lateral) it may additionally be useful to differentiate between a miscarriage and CS pregnancy based on the location and trophoblast invasion. And it may also be useful to additional differentiate between a type 1 and type 2 CSP if in the transversal plane >50% of the gestational sac is located in the myometrium/niche. Additionally it may be helpful in the differentiation between a type 2A and type 2B. Additionally it is of use to examine the relation between pregnancy location and the uterine arteries that may be relevant if therapy is considered.

6. Additional methods / research

Colour flow Doppler

• Evaluation of circular flow around the gestational sac
• Evaluation of the placenta location
• Evaluation of the placental ingrowth and its relation to the myometrium/serosa/bladder

No consensus was reached on evaluation of the relation between gestational sac and uterine arteries, 53% of the experts found that this should be assessed. Evaluation of this relation can be useful if therapy with either MTX (methotrexate), curettage or laparoscopic niche resection is considered.

Another item that was proposed by two of the experts to evaluate with colour flow Doppler was the amount of vascularity (colour score). However this is also depended on the setting of the ultrasound machine (gain, PD setting), so if relevant agreements on used machine and settings should be made.

Pulse Doppler

There was no agreement on performance of pulse Doppler in research setting only. Those who disagreed argued that there is no benefit compared to semi quantitative assessment of amount of flow (colour score). Furthermore, there is not enough evidence that pulse Doppler is safe for the fetus. Another expert stated that if it appears to be highly correlated to abnormal placentation, it should be performed in every case of niche pregnancy.

3D Ultrasound

3D evaluation and 3D power Doppler evaluation is advised to be used in patients with a suspected CS pregnancy, as was agreed by most experts. However, there was no consensus if it should be used in basic, advanced or research setting. 47% of the experts found that it should be evaluated in research setting; 20% found that is should be evaluated in the advanced setting. There was no agreement on additional value of 3D PD, probably also because it depends on the experience also if it is used in basic, research or advanced.

MRI

The majority (73%) agreed that MRI is not of additional value to differentiate in the diagnosis of niche pregnancy. It has no additional value to experts who are used to evaluate niche pregnancy with US including the use of color doppler and no additional value to experts able to make 3D US. In case of less experienced sonographers referral to an expert center should be advised in case of a suspected type 2 CSP.

Final Question