Table 1. Summary of Studies Included in Individual Participant Data Meta-analysis.
| Source | Study name | Country | Participant birth year | Mean age at IQ assessment, y | IQ test administered | Initial eligibility criteria | Initial VPT/VLBW participants surviving to discharge, No. | Eligible VPT/VLBW adults, No. | Attrition among VPT/VLBW participants, No./total No. (%) | Attrition among VPT/ VLBW participants with childhood NSI, No./total No. (%) | VPT/ VLBW participants with adult IQ scores, No. | Term-born participants in control group, No. (age range at recruitment) | Harmonization issues | Neonatal/maternal educational data imputed for VPT/VLBW participants, % |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Heinonen et al,29 2018 | Arvo Ylppo Longitudinal Study (AYLS) | Finland | 1985-1986 | 26 | WAIS-III | GA <37 wk (reduced to VPT/VLBW for this analysis) | 108 | 68 | 40/68 (58.8) | 12/15 (80.0) | 28 | 303 (infancy) | None | 0 |
| Madzwamuse et al,8 2015 | Bavarian Longitudinal Study (BLS) | Germany | 1985-1986 | 26 | WAIS-III | VPT/VLBW (GA <32 wk or BW <1500 g) | 510 | 411 | 208/411 (50.6) | 69/91 (75.8) | 203 | 192 (infancy) | None | <1 |
| Linsell et al,7 2018 | EPICure | United Kingdom and Ireland | 1995 | 19 | WAIS-II | EPT (GA <26 wk) | 315 | 306 | 182/306 (59.5) | 41/55 (74.5) | 124 | 64 (6 or 11 y) | None | 1 |
| Pyhala et al,30 2011 | Helsinki Study of Very Low Birth Weight Adults (HESVA) | Finland | 1978-1985 | 25 | WAIS-III | VLBW (<1500 g) | 334 | 254 | 145/254 (57.1) | 11/16 (68.8) | 109 | 98 (adulthood) | Maternal educational level measured in adulthood; NSI did not include IQ <70 and could not differentiate ambulatory/nonambulatory cerebral palsy | 4 |
| Lærum et al,31 2019 | Norwegian University of Science and Technology (NTNU) study | Norway | 1986-1988 | 26 | WASI | VLBW (<1500 g) | 86 | 82 | 31/82 (37.8) | 6/10 (60.0) | 51 | 75 (infancy) | Maternal educational level measured at 14 y | 6 |
| Darlow et al,32 2020 | New Zealand Very Low Birth Weight (NZ-VLBW) study | New Zealand | 1986 | 28 | WASI-II | VLBW (<1500 g) | 338 | 323 | 98/323 (30.3) | 16/25 (64.0) | 225 | 100 (adulthood) | None | 1 |
| Kroll et al,33 2017 | University College London Hospitals (UCLH) study | United Kingdom | 1979-1984 | 30 | WAIS-II | VPT (GA <33 wk, reduced to VPT/VLBW for this analysis) | 302a | 220a | 98/220 (44.5) | 11/13 (84.6) | 104 | 89 (adulthood) | BPD not available so was fully imputed; maternal educational level reported by participant in adulthood; NSI solely based on IQ <70 at 8 y | 21 |
| Doyle et al,34 2015 | Victorian Infant Collaborative Study (VICS) | Australia | 1991-1992 | 18b | WAIS-II | EPT/ELBW (GA <28 wk or BW <1000 g) | 299 | 277 | 53/277 (19.1) | 16/43 (37.2) | 224 | 146 (infancy) | None | 6 |
Abbreviations: BPD, bronchopulmonary dysplasia; BW, birth weight; EPT/ELBW, extremely preterm or extremely low birth weight; GA, gestational age; NSI, neurosensory impairment; VPT/VLBW, very preterm or very low birth weight; WAIS-II, Wechsler Adult Intelligence Scale, Second Edition (1981); WAIS-III, Wechsler Adult Intelligence Scale, Third Edition (1997); WASI, Wechsler Abbreviated Scale of Intelligence (1999); WASI-II, Wechsler Abbreviated Scale of Intelligence, Second Edition (2011).
Cohort information regarding attrition, eligible adult sample, and initial sample from the Kroll et al UCLH study33 was based on the <33 weeks’ gestational age criteria rather than the VPT/VLBW criteria (gestational age <32 weeks or birth weight <1500 g) that was used in subsequent studies. Although 122 individuals who were born preterm (<33 weeks’ gestation) participated in the study in adulthood, only 104 adults were VPT/VLBW and included in the present meta-analysis.
This study only used data from the follow-up at age 18 years. Not all participants were strictly aged 18 years; therefore, the mean age was used.