Table 1.

Characteristics of the extremely preterm (EPT), very preterm (VPT), moderately preterm (MPT) and term-born control groups

	I EPT (GA 23–27 weeks) n = 73	II VPT (GA 28–31 weeks) n = 42	III MPT (GA 32–36 weeks) n = 19	IV Term (GA ≥ 37 weeks) n = 94
Birthweight SDS*	−0.7 (0.99)	−1.9 (1.59)	−4.0 (1.5)	n.a.†
Neonatal medical complications‡	48%	8.3%	4%	0%
Males	47%	44%	52%	47%
Mothers age at child’s birth§	31.9 (5.6)	32.4 (5.3)	32.3 (6.1)	30.9 (5.0)
Mother’s education¶	4.2 (1.5)	3.9 (1.2)	4.3 (1.5)	4.0 (1.4)
Father’s education¶	4.1 (1.6)	3.9 (1.4)	4.3 (1.5)	4.0 (1.4)

^*Intrauterine growth expressed as Birth Weight Standard Deviation Score, BWSDS; Niklasson & Albertsson-Wikland, 2008.

^†Term-born controls all had a BW > 2500 g.

^‡Having one or more of the following neonatal medical complications: intraventricular haemorrhage, grades III–IV; periventricular leukomalacia, grades III–IV; chronic lung disease, grades 3+; retinopathy of prematurity, grades 3+.

^§Expressed as mean (SD).

^¶Parents’ educational level, mean (SD) based on the classification used by Statistics Sweden (2000): 0 = no formal education, 1 = not finished elementary school, 2 = graduated from junior high school, 3 = completed 2 years of high school, 4 = completed 3 years of high school education, 5 = Bachelor’s degree, 6 = Master’s degree, 7 = Doctorate degree.