The influence of maternal smoking and LBW incidence is studied. Detailed smoking history is taken at first antenatal visit and smoking history and birth weight were studied later. The type of study is
**Core Concept**
The question tests the understanding of the study design used to investigate the association between maternal smoking and low birth weight (LBW). This involves the concept of observational studies, specifically the type of study that captures data retrospectively.
**Why the Correct Answer is Right**
The study described is an example of a **retrospective cohort study**. In this design, the study population is identified based on exposure status (maternal smoking) at a single point in time (first antenatal visit), and outcomes (LBW) are then measured retrospectively. This type of study is useful for investigating the temporal relationship between exposure and outcome, but it is limited by recall bias, as the accuracy of exposure data depends on the patient's memory.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a **case-control study** typically involves selecting participants based on the presence or absence of the outcome (LBW) and then retrospectively assessing exposure status (maternal smoking). This is the opposite of the scenario described.
**Option B:** This option is incorrect because a **cross-sectional study** involves measuring both exposure and outcome at a single point in time, which doesn't fit the scenario described where exposure is assessed at the first antenatal visit and outcome is measured later.
**Option C:** This option is incorrect because an **experimental study** involves manipulating the exposure (e.g., smoking cessation program) and measuring the outcome, which is not the case in the described scenario.
**Clinical Pearl / High-Yield Fact**
When designing observational studies, it's essential to consider the potential for bias, such as recall bias, and to use data collection methods that minimize these risks.
**Correct Answer:** D. Retrospective cohort study.