title: Realizing a desired family size: when should couples start?
abstract: OBJECTIVE
  Until what age can couples wait to start a family without compromising their chances of realizing the desired number of children?
  
  
  CONCLUSIONS
  The latest female age at which a couple should start trying to become pregnant strongly depends on the importance attached to achieving a desired family size and on whether or not IVF is an acceptable option in case no natural pregnancy occurs.
  
  
  BACKGROUND
  It is well established that the treatment-independent and treatment-dependent chances of pregnancy decline with female age. However, research on the effect of age has focused on the chance of a first pregnancy and not on realizing more than one child.
  
  
  METHODS
  An established computer simulation model of fertility, updated with recent IVF success rates, was used to simulate a cohort of 10 000 couples in order to assess the chances of realizing a one-, two- or three-child family, for different female ages at which the couple starts trying to conceive.
  
  
  METHODS
  The model uses treatment-independent pregnancy chances and pregnancy chances after IVF/ICSI. In order to focus the discussion, we single out three levels of importance that couples could attach to realizing a desired family size: (i) Very important (equated with aiming for at least a 90% success chance). (ii) Important but not at all costs (equated with a 75% success chance) (iii) Good to have children, but a life without children is also fine (equated with a 50% success chance).
  
  
  RESULTS
  In order to have a chance of at least 90% to realize a one-child family, couples should start trying to conceive when the female partner is 35 years of age or younger, in case IVF is an acceptable option. For two children, the latest starting age is 31 years, and for three children 28 years. Without IVF, couples should start no later than age 32 years for a one-child family, at 27 years for a two-child family, and at 23 years for three children. When couples accept 75% or lower chances of family completion, they can start 4-11 years later. The results appeared to be robust for plausible changes in model assumptions.
  
  
  CONCLUSIONS
  Our conclusions would have been more persuasive if derived directly from large-scale prospective studies. An evidence-based simulation study (as we did) is the next best option. We recommend that the simulations should be updated every 5-10 years with new evidence because, owing to improvements in IVF technology, the assumptions on IVF success chances in particular run the risk of becoming outdated.
  
  
  CONCLUSIONS
  Information on the chance of family completion at different starting ages is important for prospective parents in planning their family, for preconception counselling, for inclusion in educational courses in human biology, and for increasing public awareness on human reproductive possibilities and limitations.
  
  
  BACKGROUND
  No external funding was either sought or obtained for this study. There are no conflicts of interest to be declared.
authors.affiliation: Department of Public Health, Erasmus University Medical Center, PO Box 2040, 3000 CA Rotterdam, The Netherlands j.d.f.habbema@erasmusmc.nl.
authors.forename: J Dik F
authors.initials: JD
authors.lastname: Habbema
authors.affiliation: Julius Centre, University Medical Center Utrecht, PO Box 85500, Utrecht 3508 GA, The Netherlands.
authors.forename: Marinus J C
authors.initials: MJ
authors.lastname: Eijkemans
authors.affiliation: Institut National d'Etudes Démographiques, 133 Bd Davout, 75980 Paris cedex 20, France.
authors.forename: Henri
authors.initials: H
authors.lastname: Leridon
authors.affiliation: Department of Public Health, Erasmus University Medical Center, PO Box 2040, 3000 CA Rotterdam, The Netherlands.
authors.forename: Egbert R
authors.initials: ER
authors.lastname: te Velde
mesh_terms: D000328:Adult; D000367:Age Factors; D003198:Computer Simulation; D005060:Europe; D005191:Family Characteristics; D005260:Female; D005298:Fertility / Q000502:physiology*; D005307:Fertilization in Vitro / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male
keywords: delay of childbearing; family planning; natural fertility; preconception counselling; reproductive failure