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Table 1 Demographic characteristics and FET parameters of the study population according to the initial day of estrogen usage

From: The timing for initiating estrogen stimulation in artificial cycle for frozen-thawed embryo transfer can be flexible

Parameters Early initiation group (n = 128) Late initiation group (n = 532) p value
Age, years 30 (28, 34) 30 (27, 32) 0.063
BMI, kg/m2 21.8 (20.1, 24.6) 22.0 (20.0, 24.5) 0.830
Infertility type, n (%)    0.486
 Primary 77 (60.2) 302 (56.8)  
 Secondary 51 (39.8) 230 (43.2)  
Infertility duration, years 3 (2, 5) 4 (2, 5) 0.228
Infertility factor, n (%)    0.061
 Tubal factor 69 (53.9) 219 (41.2)  
 Male factor 19 (14.8) 93 (17.5)  
 Mixed male and female factor 33 (25.8) 191 (35.9)  
 Unexplained 7 (5.5) 29 (5.5)  
Menstruation, n (%)    0.993
 Regular 69 (53.9) 287 (53.9)  
 Irregular 59 (46.1) 245 (46.1)  
Duration of estrogen usage, days 14 (11, 16) 11 (9, 14) < 0.001
Endometrial thickness at initial day of estrogen usage, mm 5.0 (4.1, 5.8) 5.9 (4.0, 5.7) 0.469
Peak endometrial thickness, mm 8.0 (7.4, 9.5) 8.4 (7.8, 9.5) 0.037
Optimal embryos transferred, n (%) 107 (83.6) 465 (87.4) 0.255
Biochemical pregnancy, n (%) 70 (54.7) 362 (68.0) 0.004
Clinical pregnancy, n (%) 66 (51.6) 342 (64.3) 0.008
Ongoing pregnancy, n (%) 60 (46.9) 290 (54.5) 0.120
  1. The continuous data were expressed as median (lower and upper quartiles)