Figure 2.

Design of questionnaire applied for data collection: (A) Checking procedures at the top of questionnaire (data collection finished, checked, and inserted) and examples of identification data (name, address, institution, case/control, age, ethnicity/skin color, marital status, literacy, etc.). (B) Information on causal conditions for preterm birth (spontaneous, premature rupture of membranes, or therapeutic). The same information in grey shadowed boxes should be extracted from the clinical records.