Table 1 Baseline characteristics of the sample population stratified by ovulation induction method
| Characteristic | Natural cycle (n = 1716) | one growth follicle in HMG cycle (n = 1569) | two growth follicles in HMG cycle (n = 288) | one growth follicle vs. natural P value | two growth follicles vs. natural P value | Differences between three groups P value |
|---|---|---|---|---|---|---|
| Maternal age (year) | 32.00 | 31.00 | 31.00 | 0.033* | 0.106* | 0.057 |
| ≤34(%) | 1286(74.94) | 1201(76.55) | 214(74.31) | 0.29 | 0.826 | |
| ≥35(%) | 430(25.058) | 368(23.45) | 74(25.69) | |||
| Maternal Body Mass Index (kg/m2) | 20.50 | 21.00 | 20.20 | 0.00* | 0.059* | 0.00 |
| ≤18.4(%) | 282(16.44) | 213(13.58) | 56(19.51) | 0.022 | 0.345 | |
| 18.5–24.9(%) | 1301(75.86) | 1182(75.38) | 213(74.21) | 0.505 | ||
| ≥25(%) | 132(7.70) | 173(11.03) | 18(6.27) | 0.468 | ||
| AFC | 15 | 15 | 16 | 0.133* | 0.229* | 0.133 |
| AMH | 3.59 | 3.92 | 3.22 | 0.289* | 0.592* | 0.505 |
| endometial thickness (mm) on the day of hCG administration | 8.78 ± 1.76 | 9.18 ± 1.90 | 9.51 ± 1.83 | 0.000 | 0.000 | |
| Estrogen on the day of hCG administration | 1090.32 ± 409.628 | 1430.56 ± 623.69 | 2404.88 ± 1023.90 | 0.000 | 0.000 | |
| mean dose of HMG (IU) | 553.11 ± 428.64 | 637.06 ± 455.92 | ||||
| Duration of infertility (year) | 3.21 ± 1.89 | 3.11 ± 1.73 | 3.69 ± 2.26 | 0.639 | 0.185 | |
| Infertility | ||||||
| primary infertility (%) | 1053(61.36) | 976(62.21) | 182(63.19) | 0.640 | 0.600 | |
| secondary infertility (%) | 663(38.64) | 593(37.79) | 106(36.81) | |||
| Infertility diagnosis | 0.890 | 0.075 | ||||
| Unexplained (%) | 737(42.95) | 665(42.38) | 115(39.93) | |||
| Cervical infertility (%) | 3(0.17) | 3(0.19) | 3(1.04) | |||
| Semen factor (%) | 889(51.80) | 812(51.75) | 155(53.82) | |||
| Endometriosis (%) | 87(5.07) | 89(5.67) | 15(5.208) | |||