Impact of fertility postponement on waiting time to pregnancy and reproductive failure

Krzysztof Tymicki, Warsaw School of Economics

Changes in the timing of first birth constitute one of the most prominent and well explored issues in modern demography. However, surprisingly little research has been focused on biological consequences of late reproduction. These consequences are related to so-called reproductive ageing which manifest itself in a significant and constant decrease in female fecundity beyond age of 30. We presume that late efforts to conceive, might have a substantial effect on lengthening waiting time-to-pregnancy (number of ovulatory cycles preceding conception) and may lead in a extreme case to reproductive failure. It is also plausible to assume that late attempts to conceive leave less time for efficient ad successful use of assisted reproductive technologies. In the present study we aim at analysis of interrelation between fertility postponement and reproductive ageing measured by waiting-time-to-pregnancy. According to the main hypothesis, waiting time to pregnancy should increase with age of spouses. Using event history analysis we aim at finding the threshold age beyond which we observe increase in probability of reproductive failure. This threshold constitutes a natural limit to the postponement of reproduction. We use data from the first wave of the Polish GGS survey. In the standard GGS module on fertility we have included a set of questions which measure waiting time to pregnancy (from onset of deliberate efforts to conceive). The pilot study reveals that more than 70% of couples conceive within 3 ovulatory cycles of unprotected intercourse, although we observe a significantly lower rate of success (longer duration) for females over age of 30. Discussion of the results includes considerations concerning the effects of sub-fertility and reproductive failure on the increase in rates of involuntary childlessness and decrease in parity progression ratios. Furthermore we relate these issues to below replacement TFR and possible effects of reproductive ageing and late fertility on TFR.