Ob/ Gyn Journal Club Notes

Ob/Gyn Journal Club Notes December 7, 2018 Martha A. Wojtowycz, PhD

Learning Objectives • Explain what is meant by allocation concealment and what purpose it serves in a randomized control study • Disseminate the results of a RCT • Interpret the Number Needed to Treat (NNT) • Compare and contrast the absolute risk reduction and the relative risk • Distinguish between cost benefit and cost effectiveness analysis

Balogun OA, et al. “Serial Third-Trimester Ultrasonography Compared With Routine Care in Uncomplicated Pregnancies”, Obstetrics and Gynecology, vol. 132, no. 6, December 2018.

Study Design • Randomized control trial in a single center • Why RCT? • Comparison of two treatment options • Routine care vs. serial ultrasound examinations • Feasible to randomize • Ethical • Want to control for selection bias and confounding

Allocation Concealment • Person randomizing the patient does not know what the next treatment allocation will be • Purpose is to avoid selection bias – i.e., a systematic difference in patient characteristics in the different arms of the study • Was the allocation concealed in the study? • Allocation sequence designed by statistician who was not involved in the rest of the study

Blinding • No blinding of patients, ultrasonographers, and MFM attendings reviewing the sonos, and chart abstractors • Lack of blinding has been associated with overestimation of treatment effects • If do not blind, then it is important to have an outcome measure that is less influenced by the observer • Try to use observers not involved in patient care to asses outcome without knowing which treatment arm the patient is in

Could any of these been blinded? • Patients – would be difficult to do • Sonographers – need to know why they are doing the test, e.g., discrepancy in gestational age and measurement of the fundus • Better if same group of sonographers used for both arms to ensure consistency in images

Could any of these been blinded? • Maternal Fetal Medicine attendings– • Definitions for primary and secondary outcomes clearly stated and followed • Could the MFM contribute to bias? • Chart abstractor – should have been blinded • Not done due to limited resources • Include chart abstraction funds in budget for clinical trial • Did not determine primary and secondary outcomes

Flow Diagram Very Important in Publication of RCT Need some idea of the proportion that will be excluded Need an estimate of the proportion that will decline

Table 1 does not contain p values. No statistically significant differences between the two groups. Most comparisons can be made by just by looking at the characteristics of the two groups. Tables should stand alone. Include p values?

Very uncommon to report both RR and CI for some indicators and p values for others in the same table.

Relative Risk = incidence in treatment group / incidence in control group; RR for Primary Composite Outcome = 27/8 = 3.4

Number Needed to Treat (NNT) • NNT is the number of patients you need to treat to have an impact on one person • In this study NNT = 5 • Need to treat five patients with serial ultrasound examinations to have an effect on one patient • NNT = 1/ ARR where ARR is the absolute risk reduction (reduction in the risk of the outcome) • Equal to the control event rate (ARC) minus the treatment event rate (ART) • RR = ART / ARC

Study underpowered for individual components of composite outcome. Look at the size of the 95% CI and if 1.0 is included in the confidence interval. Very large interval due to small numbers.

No statistically significant difference; 1.0 is in the 95% confidence interval for the relative risk. Underpowered.

Economic Considerations • Cost benefit analysis – compares cost of the intervention with savings from reduced medical care costs associated with diagnosing the outcome sooner • Is it worth paying for these additional ultrasounds from an economic standpoint? • Cost effectiveness analysis – compares the two options and determines which one has the lower cost per adverse outcome averted

Ob/ Gyn Journal Club Notes