Table 1. Background characteristics of singletons born after ART and spontaneous conception between 1984 to 2015a in Sweden, Norway, Finland, and Denmark, and their mothers.
| Characteristic | All countries n = 7,697,114 |
Norway n = 1,808,006 |
Sweden n = 3,136,414 |
Finland n = 1,453,949 |
Denmark n = 1,298,745 |
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|---|---|---|---|---|---|---|---|---|---|---|
| ART n = 122,429 |
SC n = 7,574,685 |
ART n = 24,114 |
SC n = 1,783,892 |
ART n = 46,974 |
SC n = 3,089,440 |
ART n = 22,046 |
SC n = 1,431,903 |
ART n = 29,295 |
SC n = 1,269,450 |
|
| Child characteristics | ||||||||||
| Calendar year of birtha, n (%) | ||||||||||
| 1984–1990 | 968 (0.8) |
1,073,580 (14.2) |
477 (2.0) |
375,572 (21.1) |
461 (1.0) |
633,618 (20.5) |
30 (0.1) |
63,869 (4.5) |
0 (0.0) |
0 (0.0) |
| 1991–1995 | 6,531 (5.3) |
1,289,711 (17.0) |
1,343 (5.6) |
290,460 (16.3) |
2,818 (6.0) |
551,451 (17.9) |
1,706 (7.7) |
313,763 (21.9) |
664 (2.3) |
134,001 (10.6) |
| 1996–2000 | 17,398 (14.2) |
1,299,565 (17.2) |
2,496 (10.4) |
284,106 (15.9) |
5,602 (11.9) |
420,635 (13.6) |
4,407 (20.0) |
276,492 (19.3) |
4,893 (16.7) |
317,969 (25.1) |
| 2001–2005 | 24,306 (19.9) |
1,296,763 (17.1) |
3,992 (16.6) |
269,009 (15.1) |
8,617 (18.3) |
454,500 (14.7) |
4,574 (20.8) |
269,749 (18.8) |
7,123 (24.3) |
303,349 (23.9) |
| 2006–2010 | 34,405 (28.1) |
1,375,332 (18.2) |
7,274 (30.2) |
284,711 (16.0) |
12,615 (26.9) |
505,882 (16.4) |
5,622 (25.5) |
284,489 (19.9) |
8,894 (30.4) |
300,158 (23.6) |
| 2011–2015 | 38,821 (31.7) |
1,241,480 (16.4) |
8,532 (35.4) |
280,434 (15.7) |
16,861 (35.9) |
523,354 (16.9) |
5,707 (25.9) |
223,541 (15.6) |
7,721 (26.4) |
213,973 (16.9) |
| Birth weight, n (%) | ||||||||||
| >4,000 g | 18,910 (15.5) |
1,400,195 (18.5) |
3,779 (15.7) |
342,675 (19.2) |
7,565 (16.1) |
576,246 (18.6) |
3,413 (15.5) |
263,515 (18.4) |
4,153 (14.2) |
217,759 (17.2) |
| Low birth weight, <2,500 g | 7,008 (5.7) |
248,605 (3.3) |
1,429 (5.9) |
61,381 (3.4) |
2,525 (5.4) |
98,611 (3.2) |
1,187 (5.4) |
41,931 (2.9) |
1,867 (6.4) |
46,682 (3.7) |
| Very low birth weight, <1,500 g | 1,592 (1.3) |
45,304 (0.6) |
347 (1.4) |
11,266 (0.6) |
541 (1.2) |
16,667 (0.5) |
241 (1.1) |
7,122 (0.5) |
463 (1.6) |
10,249 (0.8) |
| Birth weight (grams), mean (SD) | 3,442 (624) |
3,541 (565) |
3,441 (633) |
3,548 (571) |
3,457 (612) |
3,543 (559) |
3,455 (598) |
3,552 (542) |
3,405 (652) |
3,515 (592) |
| Missing, n (%) | 298 (0.2) |
31,922 (0.4) |
13 (0.1) |
1,435 (0.1) |
123 (0.3) |
6,500 (0.2) |
8 (0.0) |
3,285 (0.2) |
154 (0.5) |
20,702 (1.6) |
| LGA, n (%) | 5,305 (4.3) |
355,018 (4.7) |
1,035 (4.3) |
83,328 (4.7) |
2,080 (4.3) |
142,628 (4.6) |
972 (4.4) |
67,953 (4.8) |
1,218 (4.2) |
61,109 (4.8) |
| SGA, n (%) | 5,842 (4.8) |
272,604 (3.6) |
1,234 (5.1) |
72,908 (4.1) |
2,222 (4.6) |
104,255 (3.4) |
876 (4.0) |
45,451 (3.2) |
1,510 (5.2) |
50,119 (4.0) |
| Gestational age, n (%) | ||||||||||
| Post-term birth (≥42 weeks) | 6,877 (5.6) |
536,891 (7.1) |
1,458 (6.1) |
166,671 (9.3) |
3,098 (6.6) |
219,554 (7.1) |
924 (4.2) |
67,522 (4.7) |
1,397 (4.8) |
83,144 (6.6) |
| Preterm birth (<37 weeks) | 9,630 (7.9) |
362,575 (4.8) |
1,977 (8.2) |
88,156 (4.9) |
3,547 (7.6) |
151,560 (4.9) |
1,738 (7.9) |
61,643 (4.3) |
2,368 (8.1) |
61,216 (4.8) |
| Very preterm birth (<32 weeks) | 1,773 (1.5) |
51,101 (0.7) |
408 (1.7) |
13,750 (0.8) |
635 (1.4) |
20,169 (0.7) |
263 (1.2) |
8,164 (0.6) |
467 (1.6) |
9,018 (0.7) |
| Extremely preterm birth (<28 weeks) | 643 (0.5) |
16,716 (0.2) |
128 (0.5) |
4,719 (0.3) |
219 (0.5) |
6,393 (0.2) |
101 (0.5) |
2,761 (0.2) |
195 (0.7) |
2,843 (0.2) |
| Gestational age (days), mean (SD) | 276 (43.1) |
278 (12.9) |
277 (92.2) |
279 (13.9) |
277 (15.1) |
278 (12.7) |
276 (14.6) |
278 (11.9) |
276 (16.0) |
278 (12.9) |
| Missing, n (%) | 358 (0.3) |
116,159 (1.5) |
109 (0.5) |
78,693 (4.4) |
25 (0.1) |
3,140 (0.1) |
46 (0.2) |
6,477 (0.5) |
178 (0.6) |
27,849 (2.2) |
| Any major birth defect, n (%)b | 5,232 (4.3) |
229,754 (3.0) |
1,174 (4.9) |
58,314 (3.3) |
1,699 (3.6) |
80,488 (2.6) |
958 (4.3) |
46,267 (3.2) |
1,401 (4.8) |
44,685 (3.5) |
| Congenital heart defect, n (%)c | 1,565 (1.3) |
65,806 (0.9) |
307 (1.3) |
12,535 (0.7) |
436 (0.9) |
24,569 (0.8) |
447 (2.0) |
17,913 (1.3) |
375 (1.3) |
10,799 (0.9) |
| Cesarean delivery, n (%) | 32,041 (26.2) |
1,095,906 (14.5) |
5,719 (23.7) |
239,538 (13.4) |
12,180 (25.9) |
422,116 (13.7) |
6,117 (27.8) |
218,410 (15.3) |
8,025 (27.4) |
215,842 (17.0) |
| Follow-up time (years), mean (SD), median (range) | 8.6 (6.2), 7.5 (0.0–31.5) |
14.0 (8.6), 13.6 (0.0–32.0) |
8.5 (6.5), 7.0 (0.0–31.5) |
15.6 (9.2), 15.7 (0.0–32.0) |
8.5 (6.4), 7.1 (0.0–30.6) |
15.1 (9.2), 15.0 (0.0–31.0) |
9.4 (6.3), 8.6 (0.0–24.2) |
12.7 (7.4), 12.8 (0.0–25.0) |
8.2 (5.4), 7.5 (0.0–20.5) |
10.5 (6.1), 10.5 (0.0–21.0) |
| Maternal characteristics | ||||||||||
| Age at delivery, (years), mean (SD) | 33.9 (4.3) |
29.7 (5.2) |
33.6 (4.2) |
29.2 (5.2) |
34.2 (4.2) |
29.7 (5.2) |
34.0 (4.7) |
29.8 (5.3) |
33.7 (4.2) |
30.1 (4.9) |
| Primiparous, n (%) | 82,934 (67.7) |
3,163,018 (41.8) |
15,329 (63.6) |
738,263 (41.4) |
33,367 (71.0) |
1,310,160 (42.4) |
14,711 (66.7) |
577,369 (40.3) |
19,527 (66.7) |
537,226 (42.3) |
| Smoking at first visit to antenatal clinic, n (%) | 6,868 (5.6) |
964,044 (12.7) |
1,204 (5.0) |
125,510 (7.0) |
1,862 (4.0) |
430,120 (13.9) |
1,369 (6.2) |
219,489 (15.3) |
2,433 (8.3) |
188,925 (14.9) |
| Missing, n (%) | 10,383 (17.8) |
1,314,320 (25.1) |
5,664 (23.5) |
979,902 (55) |
2,537 (5.4) |
169,567 (5.5) |
312 (1.4) |
36,405 (2.5) |
1,870 (6.4) |
128,447 (10.1) |
| BMI (kg/m2) at first visit to antenatal clinic, mean (SD) | 24.2 (4.1) |
24.1 (4.5) |
24.3 (4.3) |
24.3 (4.8) |
24.4 (3.9) |
24.0 (4.3) |
24.1 (4.3) |
24.3 (4.8) |
23.9 (4.3) |
24.3 (5.0) |
| Missing, n (%) | 41,222 (33.7) |
3,716,763 (49.1) |
16,299 (67.6) |
1,534,660 (86.0) |
5,057 (10.8) |
662,981 (21.4) |
9,545 (43.2) |
846,434 (59.1) |
10,321 (35.2) |
672,688 (53.0) |
| Highest educational leveld, n (%) | ||||||||||
| Basic, ≤9 years | 7,363 (6.0) |
843,020 (11.1) |
NA | NA | 3,652 (7.8) |
491,066 (15.9) |
1,160 (5.3) |
155,906 (10.9) |
2,551 (8.7) |
196,048 (15.4) |
| Secondary, 10–12 years | 33,131 (27.1) |
2,316,622 (30.6) |
NA | NA | 16,044 (34.2) |
1,230,765 (39.8) |
6,293 (28.5) |
590,185 (41.2) |
10,794 (36.9) |
495,672 (39.1) |
| Tertiary, ≥13 years | 55,333 (45.2) |
2,429,890 (32.1) |
NA | NA | 25,181 (53.6) |
1,201,943 (38.9) |
14,593 (66.2) |
685,812 (47.9) |
15,559 (53.1) |
542,135 (42.7) |
| Missing | 26,602 (21.7) |
1,985,153 (26.2) |
24,124 (100) |
1,785,535 (100) |
2,097 (4.5) |
165,666 (5.4) |
0.0 (0.0) |
0.0 (0.0) |
391 (1.3) |
35,595 (2.8) |
| IVF, n (%)e | 56,216 (58.1) |
13,672 (61.0) |
27,285 (58.1) |
NA | 15,259 (55.7) |
|||||
| ICSI, n (%)e | 40,594 (41.9) |
8,745 (39.0) |
19,689 (41.9) |
NA | 12,160 (44.4) |
|||||
| Fresh embryo transfer, n (%)e | 79,816 (81.7) |
17,895 (83.6) |
36,111 (76.9) |
NA | 25,810 (88.1) |
|||||
| Frozen embryo transfer, n (%)e | 17,870 (18.3) |
3,522 (16.4) |
10,863 (23.1) |
NA | 3,485 (11.9) |
|||||
| Number of transferred embryos, mean (SD)e | ||||||||||
| SET | 47,664 (38.9) |
10,057 (41.7) |
28,289 (60.2) |
NA | 9,314 (31.8) |
|||||
| DET | 35,539 (29.0) |
10,724 (44.5) |
7,576 (16.1) |
NA | 17,237 (58.8) |
|||||
| TET | 2,179 (1.8) |
699 (2.9) |
7 (0.01) |
NA | 1,473 (5.0) |
|||||
| Missing, n (%) | 37,047 (30.3) |
2,634 (10.9) |
11,102 (23.6) |
22,046 (100) |
1,271 (4.3) |
|||||
| Any CVD before or at birth of child, n (%) | 217 (0.2) |
7,688 (0.1) |
26 (0.1) |
557 (0.03) |
91 (0.2) |
3,552 (0.1) |
50 (0.2) |
1,935 (0.1) |
50 (0.2) |
1,644 (0.1) |
| Obesity before or at birth of child, n (%)f | 4,448 (3.6) |
168,486 (2.2) |
224 (0.9) |
7,854 (0.4) |
1,321 (2.8) |
55,620 (1.8) |
206 (0.9) |
10,598 (0.7) |
2,697 (9.2) |
94,414 (7.4) |
| Any diabetes before or at birth of child, n (%) | 871 (0.7) |
34,828 (0.5) |
157 (0.7) |
4,120 (0.2) |
396 (0.8) |
17,925 (0.6) |
128 (0.6) |
6,123 (0.4) |
190 (0.7) |
6,660 (0.5) |
ART, assisted reproductive technology; BMI, body mass index; CVD, cardiovascular disease; DET, double embryo transfer; ICSI, intracytoplasmic sperm injection; IVF, in vitro fertilization; LGA, large for gestational age; NA, not available; SC, spontaneous conception; SD, standard deviation; SET, single embryo transfer; SGA, small for gestational age; TET, triple embryo transfer.
aChildren born between 1984 and 2015 in Norway, 1985 and 2015 in Sweden, 1990 and 2014 in Finland, and 1994 and 2014 in Denmark.
bMajor birth defect, registered during the first year of birth, was defined according to the EUROCAT classification system.
cCongenital heart defect was defined if the child had a diagnosis according to ICD-10 codes Q20–Q26 or ICD-9 codes 745–747 (excluding minor defects according to EUROCAT).
dHighest educational level ever registered. Information about educational level is missing for Norway.
eThe variable “number of embryos transferred” has not been in the registers during the whole study period and is completely missing in Finland since information about ART technique is not available in Finland.
fThe outpatient register started earlier in Denmark, which could be a possible explanation for the much higher prevalence of maternal obesity at birth.