Table I.
Patient characteristics and outcomes of frozen–thawed embryo transfer according to endometrial preparation protocol.
| Total population | Artificial cycle (AC) | Natural cycle (NC) | Stimulated cycle (SC) | P | |
|---|---|---|---|---|---|
| Number of FET | 14 421 | 8139 | 3126 | 3156 | |
| Age (years), mean ± SD | 34.2 | 34.1 ± 4.7 | 34.3 ± 4.5 | 34.2 ± 4.4 | 0.70 |
| Primary infertility, n (%) | 7326 (50.8) | 4182 (51.4) | 1513 (48.4) | 1541 (48.8) | 0.004 |
| Length of infertility (days), mean ± SD | 2042 ± 1054 | 2054 ± 1,059 | 2015 ± 1004 | 2035 ± 1088 | 0.92 |
| History of early pregnancy loss, n (%) | 2064 (14.3) | 1134 (13.9) | 476 (15.2) | 454 (14.4) | 0.21 |
| BMI (kg/m2), mean ± SD | 23.4 ± 5.4 | 23.8 ± 5.2 | 22.7 ± 5.8 | 23.6 ± 5.2 | 0.07 |
| Smoking, n (%) | 3390 (23.5) | 1923 (23.6) | 736 (23.5) | 731 (23.2) | 0.87 |
| ICSI, n (%) | 8321 (57.7) | 4638 (57.0) | 2036 (65.1) | 1647 (52.2) | <0.0001 |
| Endometrial thickness (mm), mean ± SD | 9.3 ± 2.5 | 9.1 ± 2.6 | 9.8 ± 2.3 | 9.1 ± 2.2 | 0.02 |
| Number of embryos transferred, mean ± SD | 1.4 ± 0.5 | 1.4 ± 0.5 | 1.3 ± 0.5 | 1.5 ± 0.5 | 0.09 |
| Biochemical pregnancy (hCG 10–100 IU/ml) per pregnancy, n (%) | 461 (10.7) | 251 (10.2) | 95 (10.5) | 115 (12.2) | 0.20 |
| Pregnancy with HCG >100 IU/ml per FET, n (%) | 3844 (26.7) | 2214 (27.2) | 812 (26.0) | 818 (25.9) | 0.20 |
| Early pregnancy loss per pregnancy with HCG >100 IU/ml, n (%) | 1210 (31.5) | 808 (36.5) | 209 (25.7) | 193 (23.6) | <0.005 |
| Live birth per FET, n (%) | 2571 (17.8) | 1375 (16.9) | 588 (18.8) | 608 (19.3) | <0.003 |
FET, frozen embryo transfer.