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The question shown is from Epidemiology Part 1 notes and reads:
Q. A study found Odds ratio of maternal hypertension to have IUGR fetus to be 1.5. What is the interpretation drawn? a. Positive association b. Common association c. Inverse association d. Rare outcome
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Answer: a. Positive association
What is an Odds Ratio (OR)?
The Odds Ratio is a measure of association used in epidemiological studies (especially case-control studies) to quantify the relationship between an exposure (here: maternal hypertension) and an outcome (here: IUGR fetus).
It is calculated as:
OR = Odds of outcome in exposed / Odds of outcome in unexposed
How to Interpret an OR
| OR Value | Interpretation |
|---|---|
| OR = 1 | No association (null value) |
| OR > 1 | Positive association - exposure increases the odds of the outcome |
| OR < 1 | Inverse (negative) association - exposure reduces the odds of the outcome |
Applying This to the Question
- The OR = 1.5
- Since 1.5 > 1, this means mothers with hypertension have 1.5 times higher odds of having an IUGR fetus compared to normotensive mothers
- This represents a positive association between maternal hypertension and IUGR
So the answer is a. Positive association.
Why the Other Options Are Wrong
- b. Common association - There is no epidemiological category called "common association"; this is a distractor
- c. Inverse association - An OR < 1 would indicate this (e.g., OR = 0.6 would mean hypertension is protective against IUGR, which makes no clinical sense here)
- d. Rare outcome - A rare outcome is relevant when discussing whether an OR approximates a Relative Risk (the rare disease assumption), but it is NOT what an OR of 1.5 directly tells you
Clinical Context
Maternal hypertension (including gestational hypertension and pre-eclampsia) causes uteroplacental insufficiency through vasospasm and reduced placental perfusion. This restricts fetal growth, making IUGR a well-known complication - entirely consistent with a positive OR > 1. This concept is reinforced in Creasy & Resnik's Maternal-Fetal Medicine, which discusses OR interpretation and the association between maternal conditions and perinatal outcomes.
Quick Rule to remember: OR > 1 = positive/direct association; OR < 1 = inverse/negative association; OR = 1 = no association.
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