Age, the desire to have a child and cumulative pregnancy rate.

The relation between women's age and fertility, and the factors that influence the age at which couples desire to have their first child, were analysed in a national sample of women aged 25-49 years. A random sample of 8050 households in the Netherlands was approached. In these households, 3295 women between the ages of 25 and 49 years answered a short questionnaire about planning their first pregnancy and about fertility. Furthermore, sociodemographic data were gathered. There appeared to be almost no variation in cumulative pregnancy rate between age 20 and 28: between 65 and 70% at 6 months, just below 90% at 12 months and approximately 93% at 24 months. After the age of 33 years, the cumulative pregnancy rate at 6 months decreased. From the age of 28 years the cumulative pregnancy rate at 12 months and at 24 months decreased gradually, reaching 75 and 80% respectively, by the age of 35 years. The year of birth of the woman (the 'time' factor) was the most important factor influencing the age at which couples desired to have their first child. In addition, demographic factors, particularly a high level of education, a high professional level and a high level of family income, were associated with the desire to have the first child at a relatively late age.