Early onset and increasing disparities in neurodevelopmental delays from birth to age 6 in children from low socioeconomic backgrounds

Table 1 Basic Sociodemographic characteristics of the participants

Characteristic		Low SES, n (%) (n = 66,325)	Intermediate SES, n (%) (n = 148,980)	High SES, n (%) (n = 60,862)
Sex
	Male	32,603 (49)	73,139 (49)	30,075 (49)
	Female	33,722 (51)	75,841 (51)	30,787 (51)
Age at 7th K-DST assessment^a		5.78 ± 0.19	5.79 ± 0.18	5.79 ± 0.18
Birth Weight		3.22 ± 0.33	3.22 ± 0.33	3.22 ± 0.33
HC z score at 4–6 mo.^b		-0.04 ± 0.99	-0.00 ± 0.98	0.05 ± 0.97
	≦ -1.65	33,722 (51)	75,841 (51)	30,787 (51)
	> -1.65	3,474 (5)	6,901 (5)	2,451 (4)
Birth Residence
	Seoul	10,946 (17)	27,709 (19)	14,510 (24)
	Metropolitan/City^c	48,294 (73)	111,013 (75)	42,782 (70)
	Rural ^c	5,843 (9)	9,512 (6)	3,387 (6)
	Missing/Etc. ^d	1,242 (2)	746 (1)	183 (0)
Birth Year
	2009	20,307 (31)	37,837 (25)	11,599 (19)
	2010	24,288 (37)	54,712 (37)	20,678 (34)
	2011	21,730 (33)	56,431 (38)	28,585 (47)
Obesity at 66–72 mo.^e
	Absence	59,842 (90)	136,700 (92)	56,445 (93)
	Presence	6,483 (10)	12,280 (8)	4,417 (7)
BMI z score at 66–72 mo.^e		0.098 ± 1.166	0.024 ± 1.120	-0.027 ± 1.092

^a Age at 7th K-DST assessment is defined as the age of the participant at the time of the 7th check-up (66-72months)
^b Obtained from the first National Health Screening Program for Infants and Children at 4–6 months after birth
^c Metropolitan areas are defined as six metropolitan cities (Busan, Incheon, Gwangju, Daejeon, Daegu, and Ulsan), cities as urban areas, and rural areas as non-city areas
^d Missing data occurred in 0.79% (2171/276167) of all birth residence data
^e Calculated by height and weight obtained from the first National Health Screening Program for Infants and Children at 66–72 months after birth
Abbreviations: BMI: body mass index; HC: head circumference; K-DST: Korean Developmental Screening Test; SES: socioeconomic status

ISSN: 1866-1955