Estimation of TTP
Figure 2A shows the estimated survival function of TTP up to 120 months, which corresponded to the elapsed time from stopping contraception to confirmation of pregnancy or until the time of the investigation in both populations of Groups 1 and 2. The mean ± SD for TTP in our study was 17.2 ± 22.7, with a median duration of 9 months and 25–75th percentiles of 3–20 months. The estimated proportion of couples who had conceived was 18.3% (n=1,447) at 3 months, 37.0% (n=2,919) at 6 months, 53.4% (n=4,216) at 12 months, 76.7% (n=6,047) at 24 months, and 85.6% (n=6,753) at 36 months (Table 2). Additionally, we represented different age patterns in women with the same method (Figure 2B). A similar scenario was also presented for the population in Group 1 (Figure 2C and Figure 2D). As can be drawn from the diagram, related curves dropped more slowly, with visible ≥30-year differences in age among subgroups.
Furthermore, we estimated the proportions of TTP at 3, 6, 12, 24, and 36 months among different age populations (Table 2). Women aged 20–24 years had the highest percentage of pregnancy at 3, 6, 12, and 24 months (23.9%, 42.5%, 58.5%, and 80.4%, respectively). Additionally, 55.8% (3,413/6,116) and 79.9% (4,885/6,116) of women aged <35 years conceived within 1 year and 2 years, respectively, and the percentage increased by only 8.4% (5,399/6116, 88.3%) in the third year. However, only 30.6% (186/607) and 50.6% (307/607) of women aged ≥35 years conceived at 1 year and 2 years, respectively.