Caesarean section in nulliparous women of advanced maternal age has been reduced in Sweden and Norway since the 1970s: a register-based study U Waldenstro ¨ m, a K Gottvall, b,c S Rasmussen d a Department of Women’s and Children’s Health, Karolinska Institutet, Stockholm, Sweden b Division of Global Health (IHCAR), Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden c Division of Epidemiology, Department of Statistics and Evaluation, National Board of Health and Welfare, Stockholm d Department of Obstetrics and Gynecology, Institute of Clinical Medicine, Haukeland University Hospital, Bergen, Norway Correspondence: Prof U Waldenstro ¨m, Bastugatan 42, 118 25 Stockholm, Sweden. Email ulla.waldenstrom@ki.se Accepted 13 August 2012. Published Online 19 October 2012. Objective To investigate rates of caesarean delivery in Sweden and Norway from 1973 to 2008 in relation to advanced and very advanced maternal age. Design Register study. Setting Sweden and Norway. Sample All nulliparous women aged over 30 years with a singleton pregnancy, with the fetus in a cephalic presentation, and delivering at term between 1973 and 2008 were evaluated. The study population comprised 329 824 women in Sweden and 127 810 women in Norway. Methods Data from the national Medical Birth Registers were used to describe caesarean section rates in three age groups: 30–34 years (reference group); 35–39 years (advanced age group); and ‡40 years (very advanced age group). Logistic regression analyses estimated the risk in each age group over four decades, in each of the two national samples. Results Caesarean delivery decreased from 1973–1979 to 2000–2008 in the two oldest age groups in Sweden (35–39 years, OR = 0.53, 95% CI = 0.50–0.58; ‡40 years, OR = 0.36, 95% CI = 0.30–0.43) and Norway (35–39 years, OR = 0.61, 95% CI = 0.54–0.68; ‡40 years, OR = 0.45, 95% CI = 0.34–0.58), but increased in women aged 30–34 years. The caesarean delivery rate in the two oldest groups peaked in the second half of the 1970s. Regardless of time point, the caesarean delivery rate was always highest in women aged ‡40 years, followed by women aged 35–39 years and lowest in women aged 30–34 years. Conclusions Caesarean delivery in nulliparous women of advanced and very advanced age peaked by end of the 1970s in Sweden and Norway. The subsequent reduction was contemporaneous with the introduction of electronic fetal monitoring and a more consistent use of the partogram, suggesting that more effective surveillance of labour increased the chance of a vaginal birth in these high-risk women. Keywords Advanced age, caesarean section, nulliparous women. Please cite this paper as: Waldenstro ¨m U, Gottvall K, Rasmussen S. Caesarean section in nulliparous women of advanced maternal age has been reduced in Sweden and Norway since the 1970s: a register-based study. BJOG 2012: DOI: 10.1111/j.1471-0528.2012.03510.x. Introduction The risk of caesarean delivery increases with maternal age, 1 and delaying childbirth until the late 30s, and beyond, has become a more frequent phenomenon over the past decades in the developed world. Delaying childbirth may therefore contribute to the rising rates of caesarean section. 2 According to the national Medical Birth Registers, introduced in Sweden in 1973 and in Norway a few years earlier, maternal age at first birth increased from means of 23.9 and 23.0 years in 1973 to 28.4 and 27.5 years in 2008 in Sweden and Norway, respectively. 3,4 During the same time period the national rates of caesarean section increased from 5.3 to 17.2% in Sweden, 3 and from 3.0 to 17.2% in Norway. 5 We are not aware of any contemporary population-based studies that have been performed in soci- eties where the postponement of childbirth has become increasingly more common that have investigated the development of caesarean section rates in women of advanced age, over a longer period of time. ª 2012 The Authors BJOG An International Journal of Obstetrics and Gynaecology ª 2012 RCOG 1 DOI: 10.1111/j.1471-0528.2012.03510.x www.bjog.org