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Explain
Reading File
Finding Sources
Finding Sources
Reading File
I now have sufficient information to give a complete, well-grounded answer.
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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