Table 1 Characteristics of study participants
Characteristics | DZT (N = 6101) | MZT (N = 164) | P value |
|---|---|---|---|
Maternal age of delivery, mean (SD), y | 31.8 (3.69) | 32.5 (4.13) | 0.061 |
Maternal age of oocyte retrieval, mean (SD), y | 30.6 (3.64) | 31.1 (4.07) | 0.121 |
Duration of infertility, mean (SD), y | 3.04 (2.48) | 3.43 (2.65) | 0.067 |
Gravidity | Â | Â | 0.591 |
 0 | 3527 (57.8%) | 89 (54.3%) |  |
 1 | 1408 (23.1%) | 39 (23.8%) |  |
 ≥2 | 1166 (19.1%) | 36 (22.0%) |  |
Primiparous status | 5661 (92.8%) | 151 (92.1%) | 0.845 |
Pregestational BMI, kg/m2 | Â | Â | 0.006 |
 <18.5 | 646 (10.6%) | 31 (18.9%) |  |
 18.5–24 | 4193 (68.7%) | 102 (62.2%) |  |
 24–28 | 959 (15.7%) | 21 (12.8%) |  |
 >28 | 235 (3.85%) | 8 (4.88%) |  |
Number of oocytes retrieved | 13.2 (7.91) | 13.1 (8.68) | 0.881 |
Fertilization method | Â | Â | 0.249 |
 IVF | 3778 (61.9%) | 107 (65.2%) |  |
 ICSI | 1533 (25.1%) | 43 (26.2%) |  |
 IVF + ICSI | 790 (12.9%) | 14 (8.54%) |  |
FET cycle rank | Â | Â | 0.524 |
 1–3 | 5746 (94.2%) | 152 (92.7%) |  |
 4–11 | 355 (5.82%) | 12 (7.32%) |  |
FET protocol | Â | Â | 0.897 |
 Natural | 1296 (21.2%) | 36 (22.0%) |  |
 HRT | 2036 (33.4%) | 52 (31.7%) |  |
 OI | 2756 (45.2%) | 76 (46.3%) |  |
Stage of embryos transferred |  |  | < 0.001 |
 D2-3 | 5351 (87.7%) | 119 (72.6%) |  |
 D5-6 | 728 (11.9%) | 44 (26.8%) |  |
 Cleavage-stage embryo + blastocyst | 22 (0.36%) | 1 (0.61%) |  |
Number of embryos transferred |  |  | < 0.001 |
 1 | 0 (0.00%) | 38 (23.2%) |  |
 2 | 6063 (99.4%) | 125 (76.2%) |  |
 3 | 38 (0.62%) | 1 (0.61%) |  |
Year of treatment | 0 (0.00%) | 38 (23.2%) | < 0.001 |
 2007–2011 | 214 (3.51%) | 16 (9.76%) |  |
 2012–2016 | 3403 (55.8%) | 87 (53.0%) |  |
 2017–2021 | 2484 (40.7%) | 61 (37.2%) |  |