Table 1. Characteristics of the included studies, ordered by gestational age categories and age of participant testing.

Author, Year (country)	Study design, total n	GA (n)	Control (n)	Age assessed (yrs)	Exclusions	Exposure measurement	Cognitive outcomes *	Adjustment
Comparison within term (37-42 weeks)
Espel et al. 2014 18 (USA)	Longitudinal prospective study N = 232	37-41 (232)	-	1	Preterm birth (<37 weeks), Post term birth (>41 weeks)	GA measured from LMP And Ultrasound	BSID II assessed by trained clinicians, no blinding	Maternal ethnicity Marital status Fetal Sex Obstetric complications Maternal education Parity Socio-economic status Birth weight percentile
Rose et al. 2013 19 (Chile)	Prospective cohort from an RCT N = 1,562	37-42 (1562)	-	1	Infants born at >42 weeks gestation, birth weight <3kg	GA based on LMP	BSID II performed by trained psychologists, blinding not reported	Fetal sex Socio-economic status Birthweight
Gyamfi Bannerman et al. 2014 21 (USA)	Prospective cohort study N = 20,093	37-42 (18,242)		4	Parents with mental retardation or alcohol or drug use	Not reported	Full-scale IQ scores from the Stanford-Binet IQ	Maternal age Maternal education Socio-economic status Smoking
Yang et al. 2009 20 (Belarus)	Prospective cohort from an RCT N = 13,824	37 (469) 38 (2100) 42 (171) 43 (10)	39-41 (11, 074)	6.5	Birth weight <2500g	GA from hospital records, 94% confirmed by ultrasound	Full-scale IQ from WASI scores performed by trained pediatricians	Maternal age Marital status Maternal education Parity Smoking Maternal height Parental occupation
Late preterm vs term (34 – 36+6)
Nepomnyaschy et al. 2011 22 (USA)	Prospective cohort study N = 5450	34-36 (400)	37-41 (5050)	2	Mothers <15 yrs, congenital anomalies, multiple births	GA measured by maternal estimated LMP	General, BSID II (converted to a percentile) mental ability, Language by trained interviewer blinded to GA	Maternal ethnicity Maternal age Marital status Fetal sex Obstetric complications Maternal Education Parity Socio-economic status Smoking
Romeo et al. 2015 23 (Italy)	Prospective cohort study N -= 119	34-36 (71)	37-41 (48)	2	Abnormal cranial Ultrasound, congenital malformations, SGA	Not reported	MDI of BSID II at 2 yrs Blinding and interviewer training not reported	Fetal sex
Narberhaus et al. 2007 24 (Spain)	Case Control study N = 64	34-36 (11)	37-41 (53)	13-14	Mental or physical disability, perinatal complications/hypoxic risk	Not reported	General WISC full scale assessed by the same psychologist	Matched by: Maternal ethnicity Maternal age Fetal sex Maternal education Socio-economic status

*Cognitive Outcomes (details in Supplementary File 4): BSID-II = Bayley Scales of Infant Development (2 ^nd Edition); MDI = Mental Developmental Index, PDI = Psychomotor Developmental Index, WISC = Wechsler Intelligence Scale for Children, WASI = Wechsler Abbreviated Scale of Intelligence