Maternal age as a predictive factor of pre-term birth. An epidemiological study from 1999 to 2008 in Greece.

The aim of the study was to estimate the risk of pre-term birth in women giving birth in Greece in different age groups. Data about women giving birth in Greece were retrieved from the Hellenic Vital Statistics covering the years from 1999 to 2008. Relative risk using χ(2) contingency tables was estimated among maternal age groups formed. These groups included mothers < 15 years of age, 15-19, 20-34 (used as a control group) and women > 34 (35-39, 40-44, 45-49 and ≥ 50) years of age. Relative risk of each age group was compared with mothers 20-34 years of age. A total of 1,069,413 valid births were included in the study and 72,156 of them were pre-term (6.75% of total count). Results exhibit a 'U'-shaped distribution of risk. Higher risk of pre-term birth is noted in the groups of < 15 years (Pearson χ(2) = 14.964, p < 0.001, risk = 1.569, CI = 1.249-1.970) and above 34 years of age (Pearson χ(2) = 2991.26, p < 0.001, risk = 1.572, CI = 1.546-1.597). For older women, a steep rise in the relative risk for pre-term birth was noted beyond the 40-44 years of age group. Finally, of interest is the fact that 'late' pre-terms (34-36 gestational weeks) account for most of the pre-term birth in mothers beyond 34 years of age.