Clinical and research implications
Human
reproduction is a complex sequence of physiological procedures starting
with gamete development, fertilization, implantation, and embryonic
development until birth.(12) Currently, with the relaxation of
population policies as well as changes in parenting attitudes and
lifestyles among young couples, the trend toward “backward”
childbearing age is gaining attention. In addition, increased changes in
environmental exposures, chromosome abnormalities, lifestyles, and
unexplained factors have exacerbated infertility.(27-29) Prevalence of
infertility using constructed methods have been extensively studied.(30,
31) Within the same study design and database, we previously utilized a
dichotomized method to estimate prevalence of infertility in different
populations: the rate was 15.5% in women at risk for pregnancy while
25% in women actively attempting to conceive.(3) Rather than
constructed measures of infertility as a parametric indicator, TTP can
present the cumulative probability of pregnancy during a certain time
period. These cumulative pregnancy prospects will help researchers grasp
the comprehensive distribution of human fecundity and decide the
appropriate timing for fertility treatment.
TTP can be obtained from various epidemiological designs. The most
common method is to ask pregnant women to retrospectively recall their
time to conception, which is easy to access with lower costs and has
been described well.(9, 13, 32, 33) However, this design may introduce
recall bias and neglect infertile couples who did not become
pregnant.(34) In contrast, a prospective design has been recognized as
the “gold standard” to estimate TTP, as it can recruit eligible
couples before their attempts and follow up their exact duration with
regular laboratory tests.(5, 10, 12, 35) However, this may be less
cost-effective for a national population level and less representative
when only focusing on pregnancy planners.(36) The current-duration
approach has become popular in recent years as it can obtain TTP from
couples who are actively attempting to conceive via a cross-sectional
study with less recall bias and better representation from the general
population.(1, 13, 32) This study design also has its weakness: 1. This
method excludes couples with successful pregnancy within the
investigated time, causing low fecundity in the certain sampled
population. 2. The TTP in these studies only include couples with the
current intention to conceive, who may differ in their pregnancy
intention and recognition of fertility status compared with all couples
at risk for pregnancy.(11) For our investigation process, we asked women
whether they were pregnant within the last 12 months and recorded their
TTP for the positive answer. For women who did not conceive within the
last 12 months, a simple question was asked to determine whether they
were currently attempting to conceive and, if so, for how long they had
attempted. Based on this cross-sectional design, our study investigated
both women who conceived within the past 12 months and women who did not
but had been actively attempting to conceive at the time of the
interview. Consequently, we collected data on their time until diagnosis
of pregnancy with either a retrospective design (among pregnant women)
or the current-duration approach (among women who did not become
pregnant but were attempting to conceive). This method could, to some
extent, overcome the limitations of previous retrospective designs and
simple current-duration approaches with minimal selection bias and
enlargement of the represented population.