Table 1.
Maternal and perinatal characteristics of the study population. Values are numbers (percentages) unless stated otherwise
|
Natural conception group (n=2915)
|
Ovarian stimulation group (n=710)
|
IVF/ICSI group (n=743)
|
|||
|---|---|---|---|---|---|
| Characteristic | Value | P value | Value | P value | |
| Mean (SD) maternal age (years) | 28.6 (4.5) | 28.7 (3.7) | 0.08 | 31.5 (3.4) | <0.001 |
| Parity: | |||||
| 0
|
1309 (44.9)
|
437 (61.5)
|
<0.001 | 509 (68.5)
|
<0.001 |
| 1
|
977 (33.5)
|
216 (30.4)
|
200 (26.9)
|
||
| ≥2 | 629 (21.6) | 57 (8.0) | 34 (4.6) | ||
| Delivery mode: | |||||
| Caesarean
|
752 (25.8)
|
242 (34.1)
|
<0.001 | 315 (42.4)
|
<0.001 |
| Vaginal | 2163 (74.2) | 468 (65.9) | 428 (57.6) | ||
| Mean (SD) gestational age (days) | 257 (20) | 254 (19) | <0.001 | 252 (19) | <0.001 |
| Gestational age <37 weeks | 1314 (45.1) | 385 (54.2) | <0.001 | 441 (59.4) | <0.001 |
| Mean (SD) birth weight* (g) | 2440 (570) | 2390 (560) | 0.02 | 2375 (570) | 0.002 |
| Birth weight <2500 g† | 1803 (61.9) | 476 (67.0) | 0.009 | 515 (69.3) | <0.001 |
ICSI=intracytoplasmic sperm injection; IVF=in vitro fertilisation.
*
Mean birth weight within groups calculated from mean birth weights of twin pairs constituting each group.
†
Defined as at least one infant with birth weight below 2500 g.