Objectives: To describe the consequences in terms of health outcomes, care and associated healthcare costs for three hypothetical cohorts of women planning their first pregnancy at a fixed, different age. Design: Decision model based on data from perinatal registries and the literature. Setting: The Netherlands. Population: 3 hypothetical cohorts of 100 000 women aged 23, 29 and 36 years, planning a first pregnancy. Main outcome measures: Live birth, pregnancy complications for mother and child and associated healthcare costs. Results: For the three cohorts of 23-, 29- and 36-yearold women, 1.6%, 4.6% and 14% of women would not succeed in an ongoing pregnancy (spontaneous or after assisted reproductive technology). The cohort aged 36 gave 9% more miscarriages, 8% more fertility treatment and 1.4% more multiple births than the cohort aged 29. The proportion of caesarean sections among low risk women was 4.9% and 11% higher respectively for the cohorts aged 29 and 36, compared with the cohort aged 23 at start. Eventually, 98%, 95% and 85% of the women in each of the three cohorts gave live birth. The costs for the two older cohorts were €415 and €1662 higher per ongoing pregnancy than the cohort aged 23 years. Conclusions: Spontaneous conception and mode of delivery are most susceptible to increasing maternal age leading to involuntary childlessness and non-spontaneous labour. The increase in assisted reproduction technology, twin pregnancies and delivery complications results in higher costs along with fewer ongoing pregnancies at higher age.