Realizing a Desired Family Size: When Should Couples Start?

Dik Habbema, Rene Eijkemans, H Leridon, Egbert Velde

Research output: Contribution to journalArticleAcademicpeer-review


Reliable methods of contraception were introduced in the1960s and enabled women to postpone childbearing and to prevent the birth of not-yet-wanted children. This allowed women to delay the start of their family. However, with increasing female age (>30 years and especially >35 years), there is increased risk of aneuploidy and either miscarriage or a deformed baby. The availability of in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) methods allows embryo selection prior to implantation in these women and birth of healthy babies. This allows older women to delay their first pregnancy and plan to have more than 1 child. As a result, the mean age of women at first childbirth increased by 4 to 5 years since the 1970s in most European countries, and the proportion who have their first child at older than 30 years has increased from about 8% to 40%. Both the treatment-independent and treatment-dependent (IVF/ICSI) chances of pregnancy decline with female age. Research on the age-dependent effects has focused on the chance of a first pregnancy and not on having more than 1 child. This study was designed to estimate at what age couples can wait to start a family without compromising their chances of realizing the desired number of children (a 1-, 2-, or 3-child family). The investigators used an established computer simulation model of fertility to simulate a cohort of 10,000 couples in order to assess the chances of realizing a 1-, 2-, or 3-child family. The model used treatment-independent pregnancy chances and pregnancy chances after IVF/ICSI updated with recent IVF success rates. Three levels of importance a couple attaches to achieving a desired family size were singled out: (i) The extremely important level is aimed for at least a 90% success chance; (ii) important (but not at all costs) is aimed at a 75% success chance; and (iii) good to have children (parenthood is not essential) is aimed at a 50% success chance. Based on the computer model, couples who wish to have at least a 90% chance to realize a 1-child family, the age for the female partner to start trying to conceive using IVF should be 35 years or younger. For those desiring 2 children using IVF, the latest starting age should be 31 years, and for 3 children, 28 years. Without IVF, couples who desire a 90% chance should start no later than age 32 years for a 1-child family, at 27 years for a 2-child family, and at 23 years for 3 children. If a 75% or lower chance is acceptable for couples attempting to conceive naturally, they can start 4 to 11 years later for a 1-, 2-, or 3-child family (at 37, 34, and 31 years of age, respectively). Use of IVF has the greatest impact on the starting age for the couples wishing a 90% chance of conceiving. For a 50% or 75% chance at older ages of realizing a 2- or 3-child family, there was little improvement for couples using IVF. The data appeared to be robust for plausible changes in model assumptions. The latest female age at which a couple should start trying to become pregnant is strongly dependent on the importance they attach to achieving a desired family size and on whether IVF is an acceptable option if no natural pregnancy occurs. In the absence of large-scale prospective studies (which would provide more conclusive data), this evidence-based simulation study is the next best option. With continuing improvements in IVF technology, the assumptions on success chances with IVF run the risk of becoming outdated. Therefore, simulations should be updated every 5 to 10 years with new evidence. These findings are important for prospective parents in family planning and for preconception counseling. This information is also useful for inclusion in educational courses in human biology and for increasing public awareness on possibilities and limitations of human reproduction.
Original languageUndefined/Unknown
Pages (from-to)629-630
Number of pages2
JournalObstetrical and Gynecological Survey
Issue number10
Publication statusPublished - 2015

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