Background: At both extremes of reproductive phase, female cycles are characterized by a high rate of anovulation, and pregnancies at these phases of reproductive span are considered as risky for obstetric complications, poor pregnancy outcome and increased maternal and newborn morbidity and mortality.
Aim: To analyse if this high rate of anovulation may be interpreted as an adaptation to poor pregnancy outcome. Therefore the association patterns between maternal age and newborn somatometric characteristics and the mode of delivery were tested.
Subjects and methods: The associations between the age as well as somatic characteristics such as pre-pregnancy weight, stature, pelvic dimensions and pregnancy weight gain of 10 765 women aged between 12 and 49 years (mean = 25.3, SD = 5.7) and newborn body dimensions and the mode of delivery were analysed.
Results: With increasing maternal age, maternal and newborn body dimensions increased significantly. Although extremely young mothers were significantly shorter and lighter and exhibited the significantly lowest pre-pregnancy weight status and the narrowest pelvic dimensions, they showed the lowest rates of caesarean sections (13.1%) and, unexpectedly, not the highest rate of low weight newborns (<2,500 g). In contrast, for mothers older than 35 years the highest rate of low weight newborns (3.7%) and the highest rate of macrosom newborns (<4,000 g) were found. Furthermore, mothers older than 40 years experienced the significantly highest rate of caesarean section (31.3%).
Conclusions: Special risks were found for mothers older than 35 years, so the lower rates of ovulatory cycles during this phase of life may be interpreted as an adaptation to increased risks for complications and poor pregnancy outcome.