Fig. 1
![Fig. 1](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs12884-018-1912-0/MediaObjects/12884_2018_1912_Fig1_HTML.png)
Flowchart of the Cohort Selection. Abbreviations: DRG = diagnosis-related group; PTB = preterm birth; PTL = preterm labour; OPS = Operationen- und Prozedurenschlüssel
Flowchart of the Cohort Selection. Abbreviations: DRG = diagnosis-related group; PTB = preterm birth; PTL = preterm labour; OPS = Operationen- und Prozedurenschlüssel