The Use of Time to Pregnancy for Estimating and Monitoring Human Fecundity From Demographic and Health Surveys

Abstract

Background: Available studies on the prevalence of infertility have proved to have certain limitations, with a scarcity of population-based studies and inconsistent reporting from surveys in countries at all income levels. We wanted to test the applicability of the current duration approach to data from the important Demographic and Health Surveys (DHS) program, funded by USAID since its inception in 1985, https://dhsprogram.com/.

Methods: The current duration approach assumes that there is a well-defined time of initiation of attempts to get pregnant and defines the current duration of a still ongoing pregnancy attempt as the time interval from initiation to interview. The DHS interviews do not have an explicit question about initiation. We focused on nullipari and substituted date of "establishment of relationship with current partner" for initiation. Our study used the current duration approach on 15 datasets from DHS during 2002-2016 in eight different countries from sub-Saharan Africa, Asia, and Latin America.

Results: Well-established statistical techniques for current duration data yielded results that for some countries postulated surprisingly long median times to pregnancy and surprisingly high estimates of infertility prevalence. Further study of the data structures revealed serious deviations from expected patterns, in contrast to our earlier experience from surveys in France and the United States where participants were asked explicitly about time of initiation of attempts to become pregnant.

Conclusions: Using cohabitation as a proxy for the initiation of attempts to get pregnant is too crude. Using the current duration approach with DHS data will require more explicit questions during the DHS interviews about initiation of pregnancy attempt.

FIGURE 1.

Reanalysis of data from French telephone survey ObsEFF¹⁵ (867 observations, of which 618 < 36 months). A: Nonparametric fits of CD distribution; B: Parametric fits of CD distribution; C: Estimated distribution of TTP.

FIGURE 2.

A: Fit of the CD distribution. Broken lines: estimated densities gP(y) and gY(y) based on all 1183 observations; the estimate of gY(0) = 1.75 while estimated gP(0) = 0.27. Fully drawn lines: estimated densities gP(y) and gY(y) based on all 1183 observations, but censoring the 538 observations larger than 36 months at 36 months. B: Estimated survival functions for times to pregnancy (TTP) based on the fits in Fig. 2A.

FIGURE 3.

Observed current durations and estimated TTP distribution for Indonesia 2012 (1183 observations, of which 645 ≤ 36 months). Acceptable histogram. TTP, times to pregnancy.

FIGURE 4.

Observed current durations and estimated TTP distribution for Nigeria 2008 (683 observations, of which 397 ≤ 36 months). Irregular histogram. TTP, times to pregnancy.

FIGURE 5.

Observed current durations and estimated TTP distribution for Colombia 2009 (456 observations, of which 168 ≤ 36 months). Flat histogram. TTP, times to pregnancy.