Table 1. Birth characteristics of infants enrolled in the study by cohort and GA group.
| COHORT | No. infants | GA weeks+days median (range) | BW grams median (range) | Swedish reference BWSDS median (range) | SGA BWSDS <−2.0 SDS Swedish reference | Canadian reference BWSDS median (range) | SGA BW <10th percentile Canadian reference | Severe growth restriction BW <3rd percentile Canadian reference | Male gender % (n) | ROP requiring treatment % (n) |
| EXPRESS | 426 | 25+4/7 | 780 | −0.68 | 16.9% | 0.13 | 9.4% | 2.1% | 54.0% | 17.1% |
| (22+1/7 to 26+6/7) | (361–1315) | (−5.18 to 3.88) | (72/426) | (−2.69 to 2.87) | (40/426) | (9/426) | (230/426) | (73/426) | ||
| North | 1772 | 28+0/7 | 1010 | −1.34 | 31.6% | −0.20 | 13.7% | 3.8% | 52.5% | 9.8% |
| American | (22+5/7 to 31+6/7) | (378–2240) | (−6.62 to 3.35) | (560/1772) | (−3.27 to 2.87) | (242/1772) | (67/1772) | (931/1772) | (173/1772) | |
| Boston | 338 | 28+5/7 | 1050 | −1.31 | 34.0% | −0.11 | 13.9% | 4.7% | 54.7% | 4.1% |
| (23+1/7 to 31+6/7) | (450–2400) | (−5.18 to 4.47) | (115/338) | (−2.58 to 3.07) | (47/338) | (16/338) | (185/338) | (14/338) | ||
| Lund | 52 | 26+1/7 | 850 | −0,77 | 25.0% | −0.01 | 7.7% | 3.8% | 51.9% | 17.3% |
| (23+0/7 to 30+5/7) | (448–1716) | (−5.00 to 0.89) | (13/52) | (−3.07 to 1.30) | (4/52) | (2/52) | (27/52) | (9/52) | ||
| Gothenburg | 353 | 29+4/7 | 1290 | −1.04 | 22.4% | 0.02 | 11.0% | 2.3% | 59.2% | 7.4% |
| (23+3/7 to 31+6/7) | (425–2210) | (−5.59 to 2.50) | (79/353) | (−2.88 to 2.47) | (39/353) | (8/353) | (209/353) | (26/353) | ||
| GA GROUP | ||||||||||
| GA 22–23 | 126 | 23+4/7 | 582 | −0.46 | 5.6% | 0.13 | 4.0% | 0% | 52.4% | 45.2% |
| wk | (22+1/7 to 23+6/7) | (361–925) | (−3.27 to 3.88) | (7/126) | (−1.56 to 2.87) | (5/126) | (66/126) | (57/126) | ||
| GA 24–25 | 690 | 25+0/7 | 720 | −0.84 | 18.0% | −0.06 | 10.6% | 2.9% | 55.2% | 24.8% |
| wk | (24+0/7 to 25+6/7) | (348–1154) | (−5.00 to 2.49) | (124/690) | (−3.07 t0 2.41) | (73/690) | (20/690) | (381/690) | (171/690) | |
| GA 26–27 | 714 | 26+6/7 | 920 | −1.16 | 26.5% | −0.03 | 11.3% | 3.8% | 51.4% | 8.1% |
| wk | (26+0/7 to 27+6/7) | (398–1430) | (−5.43 to 2.27) | (189/714) | (−2.87 to 2.28) | (81/714) | (27/714) | (367/714) | (58/714) | |
| GA 28–29 | 695 | 29+0/7 | 1180 | −1.36 | 33.1% | −0.07 | 12.5% | 3.2% | 56.0% | 1.2% |
| wk | (28+0/7 to 29+6/7) | (410–2095) | (−5.89 to 3.34) | (230/695) | (−3.09 to 2.87) | (87/695) | (22/695) | (389/695) | (8/695) | |
| GA 30–31 | 716 | 30+6/7 | 1422 | −1.67 | 40.4% | −0.32 | 17.6% | 4.6% | 52.9% | 0.1% |
| wk | (30+0/7 to 31+6/7) | (378–2400) | (−6.62 to 4.47) | (289/716) | (−3.27 to 3.07) | (126/716) | (33/716) | (379/716) | (1/716) | |
| Total | 2941 | 27+5/7 | 980 | −1.2 | 28.5% | −0.11 | 12.6% | 3.5% | 53.8% | 10.0% |
| (22+1/7 to 31+6/7) | (348–2400) | (−6.62–4.47) | (839/2941) | (−3.27 to 3.07) | (372/2941) | (102/2941) | (1582/2941) | (295/2941) |
Abbreviations: BW, indicates birth weight; BWSDS, birth weight standard deviation score; GA, gestational age; ROP, retinopathy of prematurity; SGA, small for gestational age.; wk, weeks.