Strengths and Limitations
A homogeneous group of patients was selected from women giving birth to the first or subsequent child in a public tertiary hospital with one of the largest number of deliveries per year in Poland.
The limitation of the study may be its one-center character. However, the use of electronic medical records allowed for high reliability and credibility of the research material collected in the center. The period of the study, covering 6 years, does not preclude a possible change in the standard of conduct in the course of the study, which may affect the results of the analysis. However, it allowed the recruitment of a large number of patients to the study. The studied group included 394 patients were over 40 years of age which amounted to 1.5% of the population. Probably, for this reason, no logistic regression model was built, in which age would be a significant risk factor in this subgroup of patients. The interpretation of the results for women over 40 years of age should be cautious. Patients who had experienced the study endpoint in the previous pregnancy were not excluded from the study group. There was no sufficient data on the course of previous pregnancies and deliveries, except for previous cesarean section; thus, the results should be interpreted with caution. Due to the lack of data, the socioeconomic status, educational level, height and body mass index were not evaluated. The authors are aware of a potential correlation between the above factors and the risk of adverse perinatal outcome [17, 18]. The use of nicotine and alcohol is not taken into account; however, according to the available data, this should not interfere with the results of the study [19, 20]. Advanced maternal age is not associated with more frequent smoking. On the contrary, nicotinism is more common in pregnant women under 20 years of age [16].