Realizing a desired family size: when should couples start?

Area of Science:

• Reproductive Science
• Demography
• Biostatistics

Background:

• Female fertility significantly declines with age, impacting both initial pregnancy and subsequent pregnancies.
• Previous research primarily focused on the age-related chances of a first pregnancy, not on achieving a desired family size.

Purpose of the Study:

• To determine the optimal female age for couples to start trying for a family to achieve a desired number of children.
• To assess how family size goals and the option of in vitro fertilization (IVF) influence the recommended starting age.

Main Methods:

• A fertility simulation model, incorporating current IVF success rates, was used to analyze 10,000 simulated couples.
• The model assessed the probability of achieving one-, two-, or three-child families based on the female partner's starting age.

Main Results:

• To achieve a 90% chance of a one-child family with IVF, women should start by age 35; for two children, by 31; and for three, by 28.
• Without IVF, the recommended starting ages are 32 (one child), 27 (two children), and 23 (three children).
• Accepting lower success probabilities (e.g., 75%) allows couples to start 4-11 years later.

Conclusions:

• The latest recommended age to start a family is contingent on the importance placed on family size and the willingness to use IVF.
• Simulation findings underscore the critical role of age in family planning and highlight the benefits of early conception or timely IVF consideration.
• Regular updates of simulation models are recommended to reflect advancements in IVF technology and provide current reproductive guidance.