Interpretation
In the majority of literature on the subject, the assessment of the influence of mother’s age on the course of pregnancy and delivery is based on a comparative assessment of complications occurring in different age groups. The most frequently compared groups are 35-39 and over 40 years, and the control group is composed of younger patients, also in the age groups 20-24, 25-29, 20-34 years. Grouping by age certainly facilitates the interpretation and presentation of results. Data averaging in the 5-year range (most frequently used in the literature) may, however, it harms the accuracy of the study and the strength of scientific evidence [21-24]. Age as a discrete variable allows a more precise determination of its impact on the risk of the endpoint.
Despite many studies confirming the adverse effect of increasing pregnant age on the incidence of specific complications of the course of pregnancy and delivery and perinatal failures, the standard of prenatal and perinatal care was not introduced into the clinical practice in an increasing number of patients over 35 years of age. There are limited reports that include age as a discrete variable in which attempts were made to find a safe limit regardless of age group, but the results suggest a linear increase in adverse perinatal outcomes. Importantly, in subsequent publications, a coherent threshold with significantly increased risk of obstetric complications was not specified, which confirms the thesis about the relevance of the methodology of statistical analysis adopted in this study [8, 25, 26]. Determining the exact age at which the risk of complications significantly increases is difficult. According to some researchers, a statistically significant difference in the percentage of complications occurs after 35 years of age [27, 28], according to others only after 40 years of age [29]. Some studies suggest that the risk of complications increases with age, and this increase is linear, not threshold [8, 25]. Kenny et al. suggest such dependence; however, in their study, the group was divided into 5-year age ranges, which makes it difficult to confirm this hypothesis [8]. In a similarly constructed study, Joseph et al. reported an increase in the risk of perinatal morbidity and mortality in the 35-39 group (OR 1.46, 95% CI 1.11-1.92, p = 0.007) and at least 40 years (OR 1.95, 95% CI 1.13-3.35, p = 0.02) compared to 20-24 years [30]. In turn, Ezra et al. compared perinatal results in patients over 40 years of age with patients aged 35-40. They found a similar perinatal risk in both groups, nulliparous and multiparous women [31].
In this study, showing the significant increase in the risk of a primary endpoint in the entire population (treating age as a discrete variable, without the division of subjects into age groups), the importance of age as a risk factor was confirmed. It was possible due to the inclusion of a large group of women in the analysis, which distinguishes the study.
It should be emphasized that the importance of a woman’s age in obstetric prognosis changes in the subsequent years of her life. Patients included in the study were a group of patients with low risk of complications of pregnancy and delivery. Nevertheless, the risk of the primary endpoint with each year increased more and more with the age of the patients. The importance of age as a risk factor changes over time, as illustrated in the graph in Figure 3.