Of the 18 174 children enrolled in the study, 14 350 children were determined to be full-term gestation, 773 were late preterm (35–36 6/7 weeks gestation), and 422 were moderately preterm (32–34 6/7 weeks gestation). 122 were very preterm (28–31 6/7 weeks gestation) and 35 were born extremely preterm (< 28 weeks gestation). Given the small sample size, and the focus of this study, infants less than 32 weeks were excluded from analysis. Gestational age was unable to be determined for 2 472 children as their parents did not complete the birth history section; these children were excluded from the analysis. Demographic information of the three groups of interest is shown in Table 1. For each of the participant characteristics, chi-square analysis of the three groups showed differences between groups, with p < 0.0001 for each of the characteristics. Notably, compared with full-term infants, there were more male children and more African American children in both of the preterm groups, which is similar to published data that show males and African American infants are more likely to be born preterm.21,22 More children were sampled from the southern region of the U.S., which had more preterm children compared to the other regions. In all three groups, the most common parental education level was less than four years of college.
Table 1
| | Moderately preterm | Late preterm | Full-Term |
Total, n | | 422 | 773 | 14350 |
Male, n (% weighted) | 245 (58.0) | 440 (57.0) | 7303 (50.9) |
Race, n (% weighted) | | | |
| White | 199 (47.1) | 416 (53.9) | 7466 (52.0) |
| African American | 77 (18.2) | 133 (17.2) | 1832 (12.8) |
| Hispanic | 106 (25.2) | 145 (18.7) | 3600 (25.1) |
| Asian | 18 (4.2) | 28 (3.7) | 627 (4.4) |
| Other (Hawaiian, American Indian, Alaskan native) | 23 (5.3) | 51 (6.6) | 821 (5.7) |
Attended public school, n (% weighted) | 380 (90.2) | 681 (88.1) | 12803 (89.2) |
Location, n (% weighted) | | | |
| City | 127 (30.1) | 261 (33.8) | 4461 (31.1) |
| Suburban | 139 (32.9) | 214 (27.7) | 4810 (33.5) |
| Town | 46 (10.9) | 70 (9.1) | 1590 (11.1) |
| Rural | 102 (24.1) | 200 (25.9) | 3193 (22.3) |
Region, n (% weighted) | | | |
| Northeast | 72 (17.0) | 132 (17.1) | 2277 (15.9) |
| Midwest | 79 (18.6) | 146 (18.9) | 3212 (22.4) |
| South | 197 (46.7) | 340 (44.0) | 5348 (37.3) |
| West | 75 (17.7) | 154 (20.0) | 3509 (24.5) |
Highest parental education level, n (% weighted) | | |
| No high school degree | 30 (7.1) | 48 (6.2) | 1284 (9.0) |
| High school diploma | 76 (18.1) | 145 (18.8) | 3018 (21.0) |
| < 4 years of college | 157 (37.2) | 304 (39.3) | 4802 (33.5) |
| College degree | 100 (23.7) | 177 (22.8) | 3296 (23.0) |
| Post graduate degree | 58 (13.9) | 100 (12.9) | 1901 (13.3) |
Income level of household, n (% weighted) | | |
| <$20,000 | 53 (12.5) | 117 (15.1) | 2343 (16.3) |
| $20,000–40,000 | 125 (29.5) | 154 (19.9) | 3001 (20.9) |
| $40,000–65,000 | 48 (11.4) | 107 (13.8) | 2221 (15.5) |
| $65,000-100,000 | 70(16.7) | 156 (20.1) | 2560 (17.8) |
| >$100,000 | 73 (17.3) | 132 (17.1) | 2368 (16.5) |
a Chi-square analysis of the three groups showed differences between groups, with p < 0.0001 for each of the characteristics. |
When comparing the academic scores in reading, math, and science from the direct child assessments, children born late preterm had no significant difference from full-term children in reading, math, or science (Fig. 1). Children born moderately preterm had significantly lower scores compared to full-term children for reading in kindergarten, for science in fifth grade, and for math in kindergarten, second grade, and fourth grade.
Teacher assessments were completed for each child in the study to describe if they were below, equal to, or above the average performance for grade level. When comparing children born moderately preterm to full-term children, moderately preterm children were more likely to perform significantly below grade average in reading, math, and science in kindergarten with adjusted odds ratios of 1.40 (95th percent confidence interval CI 1.03, 1.89), 1.49 (CI 1.02, 2.17), and 1.89 (CI 1.20, 2.99), respectively (Fig. 2). This trend appeared to improve over time as grade level increased. For late preterm children compared to full-term children, different trends emerged. In reading, children who were born late preterm appeared to improve as they progressed in grade level; their odds of performing below grade level dropped from 1.19 (CI 0.89, 1.60) to 0.92 (CI 0.71, 1.19) from kindergarten to fifth grade, respectively. In math, late preterm children were at higher odds of being below grade level performance as grade level increased, from 1.09 (CI 0.84, 1.42) to 1.23 (CI 0.87, 1.73). Science performance for late preterm children did not exhibit a clear trend, with an adjusted odds ratio for being below grade level that ranged from 1.05 (CI 0.83, 1.32) to 1.29 (CI 0.91, 1.81) between grades.
Individualized education plans (IEP) were on file for a significantly larger percentage of moderately preterm and late preterm children compared to full-term children in all grades from kindergarten to fifth grade (Fig. 3A). For example, at first grade, 11.8% of moderately preterm, 9.9% of late preterm, and 8.2% of full-term children had an IEP on file, while at fifth grade these percentages had increased to 18.3%, 18.3%, and 12.1%, respectively. When comparing children born moderately preterm to full-term children, the adjusted odds ratio for an IEP in a moderately and late preterm child was higher when compared to a full-term child (Fig. 4A), with the highest odds at kindergarten for both moderately and late preterm children at 2.43 (CI 1.48, 4.0) and 1.44 (CI 0.96, 2.16), respectively.
Learning disabilities were also found in a statistically significantly higher proportion in children born moderately and late preterm compared to full-term children in grades kindergarten through fifth grade (Fig. 3B). For example, in kindergarten, 29.9% of moderately preterm children, 25.0% of late preterm children, and 14.9% of full-term children had a learning disability diagnosis, while at fourth grade these percentages had shifted to 19.3%, 13.2%, and 11.0%, respectively. Learning disabilities included speech impairments, intellectual disability, visual impairments, hearing impairments, autism, and developmental delay. The adjusted odds ratio for a learning disability was elevated throughout kindergarten to fifth grade, with a 2.41 higher odds (CI 1.61, 3.60) in kindergarten (Fig. 4B). Late preterm children also had the highest odds of a learning disability in kindergarten compared to full-term children, at 2.05 time higher odds (CI 1.56, 2.69). Late preterm children continued to have elevated odds through fifth grade.