Core Outcome Measures in Effectiveness Trials

Developing a core outcome set for studies on pregnant women with Vasa Previa

General Information

Vasa Previa, a condition in which fetal vessels are present outside of the umbilical cord and course through fetal membranes, is reported to affect between 1:1275 to 1:5000 spontaneous pregnancies, and 1:202 pregnancies that result from in vitro fertilization. The proximity of the vessels to the internal os of the cervix increases the risk of haemorrhage upon spontaneous or artificial rupture of the membranes resulting in serious complications to the fetus, including hypotension, irregular heart rate and fetal death from exanguination. If Vasa Previa is not diagnosed prior to labour and vaginal delivery, approximately 60% of newborns do not survive. Early diagnosis and institution of clear management plans that in part, include an elective caesarean delivery, is therefore imperative improving outcomes in this population. However, there is no consensus on the optimal methods for diagnosis and various aspects of suggested management.

Second, women who have been diagnosed with this condition have described feeling “like a ticking time bomb” and expressed the reality of “coping with inconsistent information”. Preferences of pregnant women with the condition, and outcomes that they consider important have not yet been elucidated.

Finally, the cost implications to healthcare systems from inpatient vs. outpatient management and the use of various diagnostic modalities and management protocols have not been determined.

While these issues can be adequately addressed through well-conducted prospective studies, there is uncertainty with regard to the outcomes that should be measured in these studies that are considered important by pregnant women and other stakeholder groups including healthcare providers, researchers and policy makers. Determining this core set of outcomes that should be comprise the bare minimum for inclusion in all further studies is therefore vital.

Linda Villani, Research Student
Department of Obstetrics & Gynaecology, Mount Sinai Hospital, University of Toronto, Toronto, Canada

Dr. John Kingdom,
Division of Maternal and Fetal Medicine, Department of Obstetrics & Gynaecology, Mount Sinai Hospital, University of Toronto, Toronto, Canada

Michael Krznaric
President - International Vasa Previa Foundation

Dr. Rohan D’Souza
Division of Maternal and Fetal Medicine, Department of Obstetrics & Gynaecology, Mount Sinai Hospital, University of Toronto, Toronto, Canada

Ms. Natasha Donnolley
International Vasa Previa Foundation

Further Study Information

Current Stage:
February 2018 - 2018
Funding source(s):
The International Vasa Previa Foundation

Health Area

Disease Category
Pregnancy & childbirth

Disease Name
Vasa Previa

Target Population

Age Range
18 - 50


Nature / type of Intervention


Consensus meeting
Delphi process
Focus group(s)
Systematic review

Stage 1) Identifying core outcomes:
a) Systematic review -
A systematic review of the study reports will catalogue outcomes and outcome measures. The following two questions will be addressed and considered the primary and secondary outcome of the review:

(1) What maternal, fetal, neonatal and obstetric outcomes have been reported in studies investigating the antenatal diagnosis and management of Vasa Previa in pregnant women?
(2) How have these reported outcomes been defined and/or measured? What is the outcome reporting quality [(using the MOMENT criteria (Harman, 2013)]?

Studies will be searched using the databases MEDLINE, EMBASE and All interventions and exposures will be included. Randomized or non-randomized studies, prospective and retrospective cohort studies, and systematic reviews will be included in the search. We will exclude letters to the editor, commentaries, editorials, case-control studies, case reports and case series with less than 5 cases reported, conference abstracts that do not describe clinical outcomes and reviews that do not contain original research.

Two reviewers will extract the following data using a piloted data extraction form: publication details, study design, study aim, number of participants, primary and secondary outcomes reported, definitions of reported outcomes, tools used to measure outcomes, rationale for outcome use and methods used to enhance quality of outcome measurement. Reviewers will independently assess the quality of reporting outcomes within each study. The extracted outcomes and measures will be grouped as maternal, fetal, neonatal or obstetric. The number of studies in each group, and the study’s reporting quality score will be reported.

b) Qualitative Patient Interviews: Patients will be recruited to take part in semi-structured interviews. Interview questions will be developed in consultation qualitative research experts in conjunction with patient representatives identified through the International Vasa Previa Association, and will be guided by the literature review. Thematic content analysis will identify potential core outcomes.

c) Outcome Inventory: A comprehensive inventory of outcomes identified by the literature review and qualitative patient interviews will be developed prior to entering into the Delphi process.

Stage 2) Determining core outcomes:
Delphi methodology: Patients, their family members and patient representatives as well as other stakeholders including clinicians involved in the care of these women (maternal-fetal medicine physicians, obstetricians, obstetric nurses, neonatologists, radiologists, family doctors, specialist midwives, obstetric anaesthesiologists), researchers, administrators, policy makers and guideline developers will be invited to participate in a process that assesses the extent of agreement (consensus measurement) and then resolves disagreement (consensus development). Repeated reflection and scoring will be encouraged, to increase the likelihood of stakeholder group convergence towards consensus core outcomes. If this is not achieved, a consensus group meeting will be convened.

Stage 3) Determining How Core Outcomes Should be Measured:
a) Quality Assessment: Once core outcomes have been agreed upon, an assessment framework (truth, discrimination, feasibility) will evaluate the quality of these potential outcome measures using recommendations set out by COSMIN (COnsensus-based Standards for the selection of health Measures and INstruments). This will include evaluating the studies by statistical method, methodological quality and generalizability of the results. High-quality outcome measures will then be incorporated into the core outcome set.

b) Stakeholder Consultation: Stakeholder feedback will be collated, reviewed, and incorporated into the finalised core outcome set prior to distribution.

Stakeholders Involved

Clinical experts
Conference participants
Consumers (caregivers)
Consumers (patients)
Patient/ support group representatives
Policy makers

Study Type

COS for clinical trials or clinical research
COS for practice
Recommended outcome measures (measurement)

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