Fresh embryo transfer group N=1822
Frozen-thawed embryo transfer group N=2098
Frozen-thawed embryo transfer group N=2098
Frozen-thawed embryo transfer group N=2098
χ2/U value
P value
χ2/U value*
P value*
NC-FET group N=1353 HRT-FET group N=745
Total
Placental structural abnormalities
Velamentous placenta
55(3.0%)
45(3.3%)
27(3.6%)
72(3.43%)
0.67
0.716
0.53
0.466
Battledore placenta
93(5.1%)
80(5.9%)
43(5.8%)
123(5.86%)
1.10
0.578
1.08
0.299
others
24(1.3%)
13(1.0%)
10(1.3%)
23(1.10%)
0.99
0.609
0.40
0.526
placenta accreta 73(4.0%) 48(3.5%) 79(10.6%) 127(6.05%) 57.85 <0.001 8.44 0.004
A history of intrauterine operation
32(1.7%)
37(2.7%)
47(6.3%)
84(4.00%)
No uterine operations
41(2.3%)①②
11(0.8%)
32(4.3%)
43(2.05%)
27.97
<0.001
0.19
0.665
Placenta increta 66(3.6%) 35(2.6%) 66(8.9%)ab 101(4.81%) 49.74 <0.001 3.40 0.065
A history of intrauterine operation
38(2.1%)
23(1.7%)
47(6.2%)
70(3.34%)
No uterine operations
28(1.5%)
12(0.9%)
20(2.7%)
32(1.53%)
10.30
0.006
0.00
0.977
Placenta previa 238(13.1%) 152(11.2%) 69(9.3%) 221(10.53%) 7.84 0.020 6.03 0.014
Premature rupture of membranes 394(21.6%) 329(24.3%) 159(21.3%) 488(23.26%) 3.93 0.140 1.50 0.221
At term
327
283
129
412
Preterm
67
46
30
76
Placental abruption 10(0.6%) 7(0.5%) 7(0.9%) 14(0.67%) 1.50 0.473 0.23 0.635