From: Association between paternal age and singleton birthweight in frozen embryo transfer cycles
 | ≤ 30 years n = 2634 | 31–35 years n = 3886 | 36–40 years n = 2129 | ≥ 41 years n = 1116 | P value |
---|---|---|---|---|---|
Maternal age (year) | 28.07 ± 2.58 | 31.66 ± 2.62 | 34.91 ± 2.93 | 37.77 ± 3.67 |  < 0.001a |
Maternal BMI (kg/m2) | 21.22 ± 2.60 | 21.35 ± 2.56 | 21.66 ± 2.58 | 21.79 ± 2.48 |  < 0.001a |
Paternal education |  |  |  |  |  < 0.001b |
 Below high school | 565 (21.5) | 507 (13.0) | 345 (16.2) | 170 (15.2) |  |
 High school | 459 (17.4) | 440 (11.3) | 276 (13.0) | 173 (15.5) |  |
 College | 1553 (59.0) | 2570 (66.1) | 1281 (60.2) | 660 (59.1) |  |
 Above college | 57 (2.2) | 369 (9.5) | 227 (10.7) | 113 (10.1) |  |
Maternal education |  |  |  |  |  < 0.001b |
 Below high school | 642 (24.4) | 628 (16.2) | 371 (17.4) | 209 (18.7) |  |
 High school | 427 (16.2) | 456 (11.7) | 281 (13.2) | 160 (14.3) |  |
 College | 1525 (57.9) | 2522 (64.9) | 1303 (61.2) | 655 (58.7) |  |
 Above college | 40 (1.5) | 280 (7.2) | 174 (8.2) | 92 (8.2) |  |
Infertility cause |  |  |  |  |  < 0.001b |
 Female | 1936 (73.5) | 2857 (73.5) | 1531 (71.9) | 771 (69.1) |  |
 Male | 342 (13.0) | 408 (10.5) | 208 (9.8) | 133 (11.9) |  |
 Mixed | 319 (12.1) | 520 (13.4) | 325 (15.3) | 188 (16.8) |  |
 Unexplained | 37 (1.4) | 101 (2.6) | 65 (3.1) | 24 (2.2) |  |
Infertility duration (years) | 2.44 ± 1.83 | 3.16 ± 2.35 | 4.00 ± 3.28 | 4.18 ± 4.01 |  < 0.001a |
Parity |  |  |  |  |  < 0.001b |
 0 | 2556 (97.0) | 3681 (94.7) | 1885 (88.5) | 906 (81.2) |  |
 > 0 | 78 (3.0) | 205 (5.3) | 244 (11.5) | 210 (18.8) |  |
FET cycle rank |  |  |  |  |  < 0.001b |
 First | 1703 (64.7) | 2240 (57.6) | 1179 (55.4) | 589 (52.8) |  |
 High order | 931 (35.3) | 1646 (42.4) | 950 (44.6) | 527 (47.2) |  |
FET endometrial preparation | Â | Â | Â | Â | 0.001b |
 Natural cycle | 539 (20.5) | 898 (23.1) | 529 (24.8) | 282 (25.3) |  |
 Artificial cycle | 2095 (79.5) | 2988 (76.9) | 1600 (75.2) | 834 (74.7) |  |
Endometrial thickness (mm) |  |  |  |  |  < 0.001b |
 < 8 | 178 (6.8) | 277 (7.1) | 190 (8.9) | 132 (11.8) |  |
 8–11 | 1479 (56.2) | 2199 (56.6) | 1222 (57.4) | 627 (56.2) |  |
 > 11 | 977 (37.1) | 1410 (36.3) | 717 (33.7) | 357 (32.0) |  |
Fertilization method |  |  |  |  |  < 0.001b |
 IVF | 1614 (61.3) | 2463 (63.4) | 1309 (61.5) | 670 (60.0) |  |
 ICSI | 729 (27.7) | 1002 (25.8) | 613 (28.8) | 386 (34.6) |  |
 IVF + ICSI | 291 (11.0) | 421 (10.8) | 207 (9.7) | 60 (5.4) |  |
Number of embryos transferred | Â | Â | Â | Â | 0.583b |
 1 | 2232 (84.7) | 3272 (84.2) | 1821 (85.5) | 942 (84.4) |  |
 ≥ 2 | 402 (15.3) | 614 (15.8) | 308 (14.5) | 174 (15.6) |  |
Embryo developmental stage at transfer | Â | Â | Â | Â | 0.003b |
 Day 3 | 427 (16.2) | 694 (17.9) | 407 (19.1) | 234 (21.0) |  |
 Day 5/6 | 2207 (83.8) | 3192 (82.1) | 1722 (80.9) | 882 (79.0) |  |
Delivery mode |  |  |  |  |  < 0.001b |
 Natural birth | 845 (32.1) | 1139 (29.3) | 504 (23.7) | 219 (19.6) |  |
 Cesarean section | 1789 (67.9) | 2747 (70.7) | 1625 (76.3) | 897 (80.4) |  |