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Table 2 Pregnancy and birth outcomes compared between the immediate and delayed FET groups. Data are presented as numbers (%)

From: Immediate versus delayed frozen embryo transfer in women following a failed IVF-ET attempt: a multicenter randomized controlled trial

  Intention-to-treat analysis Per-protocol analysis
Immediate FET group Delayed FET group Relative risk (95% CI) P-value Immediate FET group Delayed FET group Relative risk (95% CI) P-value
Subjects 366 366    326 320   
Positive pregnancy 155 (42.3) 159 (43.4) 0.98 (0.83 to 1.15) 0.765 154 (47.2) 157 (49.1) 0.96 (0.82 to 1.13) 0.643
Embryo implantation 157/620 (25.3) 125/609 (20.5) 1.23 (1.00 to 1.52) 0.046 156/620 (25.2) 123/609 (20.2) 1.25 (1.01 to 1.53) 0.038
Clinical pregnancy a 137 (37.4) 111 (30.3) 1.23 (1.01 to 1.51) 0.042 136 (41.7) 109 (34.1) 1.23 (1.00 to 1.50) 0.045
Biochemical pregnancy loss 18 (11.6) 48 (30.2) 0.39 (0.24 to 0.63)  < 0.001 18 (11.7) 48 (30.6) 0.28 (0.23 to 0.63)  < 0.001
Clinical pregnancy loss b 15 (10.9) 13 (11.7) 0.94 (0.47 to 1.88) 0.850 15 (11.0) 12 (11.0) 1.00 (0.49 to 2.05) 0.996
Total pregnancy loss 33 (21.3) 61 (38.4) 0.56 (0.39 to 0.80) 0.001 33 (21.4) 60 (38.2) 0.56 (0.39 to 0.81) 0.001
Ectopic pregnancy 2 (1.3) 5 (3.1) 0.41 (0.08 to 2.08) 0.448 2 (1.3) 5 (3.2) 0.40 (0.08 to 2.04) 0.448
Multiple pregnancy 18 (13.1) 14 (12.6) 1.04 (0.54 to 2.00) 0.902 18 (13.2) 14 (12.8) 1.03 (0.54 to 1.98) 0.928
Ongoing pregnancy 122 (33.3) 98 (26.8) 1.25 (0.99 to 1.56) 0.053 121 (37.1) 97 (30.3) 1.22 (0.99 to 1.52) 0.067
Live birth 120 (32.8) 96 (26.2) 1.25 (0.99 to 1.57) 0.052 119 (36.5) 96 (30.0) 1.22 (0.98 to 1.52) 0.079
  1. Abbreviation: FET Frozen thawed embryo transfer, CI Confidence interval
  2. a In the Immediate FET group, one woman conceived naturally and delivered a healthy male infant vaginally
  3. b In the Delayed FET group, two women conceived spontaneously, however, one miscarried in the second trimester because of fetal anomalies