Delaying the start of childbearing raises the issue of fertility postponed versus fertility foregone. One of the limits of previous studies of ``How late can you wait?'' is the difficulty of controlling for sexual activity. Data on the frequency and timing of intercourse within a menstrual cycle are uncommon. We use such data from the Menstrual Cycle Fecundability Study to study ``Can we wait until the early 30s?''. We model the effect of age on conditional fecundability, i.e., the probability of conception given that the couple is not sterile, simultaneously controlling for the effect of primary sterility and the frequency and timing of intercourse in each menstrual cycle. Can we wait until the early 30s for a first birth? Our evidence is yes (providing you are not already sterile) as the increase in the mean waiting time to conception is very modest and of little practical importance.
McDonald, J. W., Rosina, A., Rizzi, E. L., & Colombo, B. (2005). Age and fertility : Can we wait until the early 30s? Applications and Policy Working Papers, Southampton Sciences Research Institute, A04/22, 22p. https://hdl.handle.net/2078.5/55680 (Original work published 2005)