To estimate associations between gestational age (GA) and teacher-reported academic outcomes at age 9 years among children born at term (37–41 weeks).
A secondary data analysis of 1405 children participating in a national US birth cohort study was conducted. At age 9 years, students were evaluated by their teachers in the areas of mathematics, science and social studies, and language and literacy. Unadjusted and adjusted logistic regression models of associations between GA and teacher-reported academic outcomes were estimated and neonatal morbidities were explored as potential pathways.
A continuous measure of GA in weeks was significantly associated with above-average rankings in all areas. The associations were similar across outcomes (eg, mathematics [odds ratio (OR): 1.13; confidence interval (CI): 1.02–1.25], science and social studies [OR: 1.13; CI: 1.01–1.26], and language and literacy [OR: 1.16; CI: 1.05–1.28]) in a model that adjusted for child sex, maternal characteristics, and obstetric risk factors and delivery complications. Other specifications indicate a positive association between late term (41 weeks) and mathematics and a negative association between early term (37–38 weeks) and language and literacy, compared with term (39–40). The associations did not appear to operate through neonatal morbidity.
The findings highlight the importance of GA, even at term. Whereas current guidelines suggest waiting until at least 39 weeks to deliver when possible, our findings add to a small group of studies suggesting that GA through 41 weeks is associated with improvements in some educational outcomes.
Extremely few studies have investigated gestational age at term and academic outcomes of children in the United States. Current recommendations, based largely on studies of neonatal outcomes, are to defer elective deliveries until at least 39 weeks’ gestation.
In this US-based study of 9-year-olds born at term, there were some associations between gestational age and academic outcomes, even at late-term. These findings suggest that the current recommendation for delaying elective deliveries to 39 weeks should be reexamined.
Extensive research has been conducted to investigate educational outcomes of very preterm infants (<32 weeks), who consistently have been found to be at high risk for poor school performance.1,2 Studies of late-preterm (34–36 weeks) infants have also revealed worse school outcomes when compared with children born at early term (37–38 weeks),3 but with much smaller decrements. Fewer studies have been focused on gestational age (GA) and educational outcomes among term births. Most of what is known in this regard comes from countries other than the United States, which lacks a national database that links birth information to educational records.
In studies from the United Kingdom, researchers found that teacher assessments of 5-year-old children in communication, math, and other areas,4 and of 7-year-old children in reading, math, speaking and listening, and science, were more favorable for children born at 39 to 41 weeks than at early term (37–38)5 and that school-aged children in Scotland born at 37 to 39 and 42 weeks had greater need for special education than those born at 40 to 41 weeks.6 In New Zealand, students aged 15 to 16 years born early term scored lower and those born at 41+ weeks scored higher on their national high school examinations compared with students born at 39 to 40 weeks.7 Studies from Australia showed inconsistent patterns.8–10 Studies from Denmark revealed that parents and teachers were more likely to report reading and spelling difficulties at ages 9 to 11 for children born early term than for those born term (39–40 weeks),11 examination grades after 9 years of school appeared to increase with each week of GA at term12 (statistical significance was not assessed), the odds of ever having participated in special education by age 16 decreased with each week of GA at term,13 the odds of finishing compulsory schooling increased with each week through 40 weeks,13 and early-term birth (versus 39–42 weeks) was associated with lower educational attainment at age 28.14 In Sweden, early-term birth (versus 39–41 weeks) was associated with lower odds of completing postsecondary education.15
Findings from other countries may not generalize to the United States because of differences in health care and education systems. Researchers in a study using birth records from Florida matched to early intervention and education records presented suggestive evidence that early-term birth was associated with worse school readiness outcomes compared with birth at higher GAs, but statistical significance was not assessed.16 Another study of 5-year-olds from a nationally representative US birth cohort revealed that reading assessments of children born at 37 weeks were significantly worse than those of children born at 40 weeks.17 A study of standardized reading and math scores of third-graders in New York City public schools linked to birth records found that a continuous measure of GA in weeks (37–41 weeks) was significantly associated with better reading and math scores and that scores for children born early term were significantly lower than those for children born at 39 to 41 weeks.18 Another study using the same New York City data found higher scores with each week of GA at term, but statistical significance was not assessed.19
In 2009, the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine published guidelines to discourage nonmedically indicated deliveries before 39 weeks after multiple studies revealed that early-term birth was associated with increased neonatal morbidity and mortality compared with deliveries at 39+ weeks. This guidance was updated in 2019 to take into account more recent evidence of adverse effects of early-term deliveries on early childhood cognitive and educational outcomes.20
We aimed to estimate associations between GA and teacher-reported academic outcomes at age 9 among infants born at term (37–41 weeks) from a national US birth cohort study that included maternal surveys, maternal and newborn hospital medical records, and teachers’ surveys. The multifaceted rich data allowed us to control for potentially confounding risk factors and to explore potential mediating effects of neonatal morbidities.
We use data from the Fragile Families and Child Wellbeing (FFCWB) study, a national birth cohort study that randomly sampled births in 75 hospitals in 20 large US cities from 1998 to 2000. By design, ∼3/4 of the mothers were unmarried. Face-to-face interviews were conducted with 4898 mothers while still in the hospital after giving birth21,22 ; additional information was collected from mothers’ and infants’ medical records from the birth hospitalization in 61 of the hospitals. The availability of medical records depended primarily on administrative processes of hospitals rather than decisions of respondents to make their records available. Mothers who completed postpartum (baseline) interviews were reinterviewed 1, 3, 5, and 9 years later. During the 9-year follow-up, interviewers obtained consent to contact the children’s teachers.
The eligible sample consisted of 3088 children born at 37 to 41 weeks’ gestation (singleton births only) with available medical record data (needed to ascertain GA) and no missing analysis variables from the postpartum survey (Fig 1). Of those, 1683 cases had no or incomplete teacher survey data, leaving an analysis sample of 1405 children.
We used a continuous measure of completed weeks’ gestation and a set of indicators for early term (37–38 weeks), term (39–40 weeks), and late term (41 weeks), as distinguished by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine.
Performance Relative to Peers
When the child was 9 years old, their teacher was asked: “Overall, how would you rate this child’s academic skills in each of the following areas, compared to other children of the same grade level?” The areas were mathematics, science and social studies, and language and literacy, and the response choices for each were far below average, below average, average, above average, or far above average. For each area, we created a binary outcome for average, above average, or far above average (versus far below average or below average) to characterize the child not being behind in terms of performance, but we assessed sensitivity to other cutoffs and to continuous measures. Additionally, we created a binary outcome for average, above average, or far above average ratings in all 3 subjects.
Adequate Performance Past Month
Teachers also completed the Cognitive Problems/Inattention Subscale of the Conners Teacher Rating Scale–Revised Short Form (CTRS-RSF),23 in which they were asked to rate children on a number of common problems children have in school. Specifically, the teacher was asked to rate the child on a scale of 0 to 3 (0 = not true, 1 = just a little true, 2 = pretty much true, 3 = very much true) for each problem in the past month. We coded the child as having performed adequately in mathematics if the teacher reported “not true” or “just a little true” for “poor in arithmetic” and in reading if the teacher reported “not true” or “just a little true” for “not reading up to par.”
Other Analysis Variables
All adjusted models controlled for the child’s sex, the mother’s first birth, and measures of socioeconomic status, including the mother’s age, race and ethnicity, foreign-born status, education, marital status, and Medicaid coverage for the delivery (versus private or other insurance), all assessed at baseline (see Table 1 for age, race and ethnicity, and education categories). Medicaid is government-provided health insurance in the United States that is available to low-income pregnant women. Some models additionally controlled for obstetric risk factors and delivery complications assessed from the mothers’ medical records (detailed lists in notes to Table 1), any prenatal smoking, late prenatal care (initiated after first trimester), missing information on prenatal care timing, and cesarean delivery. In some models, we included measures of neonatal morbidity (respiratory conditions, hypoglycemia, and hyperbilirubinemia) to explore those conditions as potential pathways between GA and educational outcomes. Supplementary models included the infant having been in a NICU as an alternative measure of neonatal morbidity and alternatively excluded children born small for gestational age and low birth weight (<2500 g) to eliminate potential confounding from those characteristics.
First, we compared our analysis sample to the cases in the full cohort (excluding multiples) of 4803 that were not in our sample using t tests (for binary variables) or χ2 tests (for categorical variables). Second, we documented children’s educational outcomes and sample characteristics, overall and by early term, term, or late term. Third, we estimated unadjusted and adjusted logistic regression models of associations between GA and children’s academic outcomes. The first adjusted model controlled for child sex and maternal characteristics, the second added obstetric risk factors and delivery complications, and the third further added neonatal morbidities. All estimates are presented as odds ratios (ORs) with 95% confidence intervals (CIs). We also replicated the full set of logistic regression analyses using inverse probability weights to account for sample loss from the eligible sample of 3188 children (Fig 1) and estimated models that limited the sample to children of United States-born mothers to further explore potential bias resulting from loss to follow-up.
Analyses were conducted by using Stata Version 15.0 (Stata Corp, College Station, TX). This study was approved by the Rutgers Biomedical and Health Sciences Institutional Review Board.
Mothers of children in the analysis sample did not differ significantly from those in the original cohort that were not in our sample in terms of education, race and ethnicity, marital status, first birth, or Medicaid status, but they were slightly younger (24.9 vs 25.4 years) and less likely to be foreign born (13.9% vs 18.6%) (not shown in tables).
Approximately 28% of the children were early term, 60% were term, and 13% were late-term (Table 1). Roughly one-half of the mothers (48%) were non-Hispanic Black, 64% had a high school education or less, and 76% were unmarried, reflecting the oversampling of nonmarital births in the FFCWB study and strong associations between nonmarital childbearing, poverty, and entrenched social disadvantages associated with racial minority status in the United States.24 Almost two-thirds of deliveries (63%) were covered by Medicaid. Of mothers with information on prenatal care timing, 51% initiated care in the first trimester (0.43/[0.43 + 0.41] = 0.51). Approximately one-fifth (18%) of the mothers smoked during pregnancy.
Average or Above-Average Student Performance
In both unadjusted and adjusted models, the continuous measure of GA in weeks was significantly associated with the odds of average or above-average rankings in mathematics, science and social studies, language and literacy, and all subjects combined at age 9 (Table 2). The associations were similar across outcomes (eg, mathematics [OR: 1.13; CI: 1.02–1.25], science and social studies [OR: 1.13; CI: 1.01–1.26], language and literacy [OR: 1.16; CI: 1.05–1.28], all subjects [OR: 1.16; CI: 1.05–1.27] in the model that adjusted for child sex, maternal characteristics, and obstetric risk factors and complications; model 3). Adjusting for socioeconomic factors attenuated the ORs somewhat, but adjusted estimates were insensitive across model specifications.
The corresponding models using indicators for early term and late-term birth (versus term) instead of the continuous measure of GA indicate positive associations between late-term birth and mathematics (eg, OR: 1.50; CI: 1.03–2.18; Model 7) and negative associations between early-term birth and language/literacy (eg, OR: 0.75; CI: 0.58–0.97; Model 7). Again, adjusted estimates were insensitive across model specifications.
Children of married and more educated mothers had higher odds of positive teacher ratings than those with unmarried and less educated mothers. Children with non-Hispanic Black mothers had worse teacher ratings than those with non-Hispanic white mothers (Table 3).
Adequate Student Performance Past Month
The patterns of estimates for this outcome were consistent with those above for performance in mathematics and language/literacy, but most estimates were not statistically significant, perhaps because the questions pertained to a short time period. A clear exception is that the associations between continuous GA and adequate performance in reading were statistically significant across all models. Again, the ORs were largely insensitive to model specification. Covariate estimates were similar to those reported on above (Supplemental Table 5).
Supplementary models that controlled for NICU stay, excluded children born small for GA, or excluded children who were low birth rate produced estimates similar to those in Tables 2 and 4, as did models that used different cutoffs for the educational outcomes, used continuous outcome measures of academic performance, or included indicators of each type of neonatal morbidity instead of the combined measure (not shown). Models that limited the sample to US-born mothers also produced similar estimates, suggesting that sample attrition by maternal nativity did not bias the estimates (not shown). Finally, using inverse probability weights to account for sample loss did not substantively or substantially change the estimates (not shown).
In a US birth cohort of children born at term (37–41 weeks), GA was positively associated with teacher-reported ratings of academic performance in mathematics, science and social studies, and language and literacy at age 9. Findings also suggested a general pattern of worse outcomes for children born at early term (37–38 weeks) and better outcomes for those born at late term (41 weeks) compared with those born at term (39–40 weeks). Compared with term, early term was negatively and significantly associated with performance in language and literacy and late-term was positively and significantly associated with performance in mathematics; the former is a common finding in the literature, whereas the latter is consistent with findings from some studies suggesting that a 41st week of GA is advantageous for academic performance.7,12,19 Corresponding analyses using teachers’ reports of adequate performance in mathematics and reading in the past month indicated the same patterns but fewer statistically significant associations.
This study adds to the previous literature, which considered a variety of educational outcomes, ages of children, and populations, by using a national US-based sample, assessing children aged >5 years, and exploring potential mediating roles of neonatal morbidities. The most comparable US-based study was focused on standardized test results at age 8 in New York City,17 whereas our study focused on teacher reports of academic performance at age 9 in a national urban sample. Test scores and teacher ratings of academic performance are distinctly different outcomes because a student can score well on a test but perform poorly in school or vice versa. As far as we know, in no previous studies have researchers explored neonatal morbidities as potential pathways linking GA to educational outcomes. We found that, although neonatal respiratory conditions, hyperbilirubinemia, and other morbidities are associated with both GA25,26 and cognitive and educational outcomes,27,28 even at term,29,30 neonatal morbidities did not appear to underlie the associations between GA and teacher-reported educational outcomes among children born at term.
Adverse effects on cognition related to earlier birth may reflect alterations in brain development postnatally compared with in utero. Brain development begins soon after conception and continues into early adulthood, but there is increasing evidence that transferring brain growth and development from an intrauterine environment to an extrauterine environment is less than optimal, even in the absence of other neurologic risk factors, and that the human brain continues to develop uniquely in utero until the end of gestation.31 Although much of neurogenesis is complete by the third trimester, the ability of neurons to communicate is just starting. Synaptogenesis increases considerably in the last 3 months of gestation and continues postnatally in a period of exuberant synaptogenesis.32 The greatest increase over the last month of gestation occurs in the visual and auditory cortex, followed by areas responsible for receptive language and speech production.33 These new synapses are the most significant contributor to brain volume growth. Quantitative MRI data demonstrate that brain tissue volume between 29 and 41 weeks increases linearly, with the most substantial portion in the cerebral cortex.34 Additionally, there is a fivefold increase in myelinated white matter between 35 and 41 weeks34 ; consequently, lower GA limits the brain’s ability to effectively transmit information between neurons. These changes in white matter microstructure are particularly associated with improved mathematics performance.35
The findings from this study also highlight the importance of disadvantaged minority status, nonmarital birth, and low maternal education as risk factors for poor school performance. These findings, in conjunction with our findings for GA, underscore the importance of comprehensive educational supports, especially in low-income neighborhoods. Children with inherent developmental risk, such as those born prematurely or with a known disability, are regularly referred for evaluation and support services, but children who are not thought of as high risk may be overlooked. Initiatives such as universal prekindergarten may help compensate for these unseen risks and provide for postpartum catch-up brain development.
A strength of this study was the use of data from a national US birth cohort study with data from medical records and maternal surveys linked to teacher surveys. These data allowed us to control for a broad array of potentially confounding socioeconomic, obstetric, and delivery-related risk factors; explore neonatal morbidities as potential pathways; and contribute to the extremely small literature on GA at term and educational outcomes in the United States.
Limitations include the urban sample and the oversampling of nonmarital births in the FFCWB study. Additionally, we relied on assessments of academic performance by teachers, which may be subjective but likely reflect students’ grades (because teachers assign the grades). Studies have found associations between teacher ratings and academic skills,36,37 and studies from other countries using teacher ratings based on different questions have had similar findings to ours.4,5,11 The questions we used to assess children’s academic performance have been used in US government surveys (including the Early Childhood Longitudinal Study-Kindergarten Cohort, which focuses on education) and a recent study of adverse childhood experiences and educational outcomes.38 Moreover, patterns of estimates were similar when using relevant components of the validated CTRS-RSF. Loss to follow-up is another limitation, although supplemental analyses suggested minimal bias owing to attrition. Finally, causality cannot be firmly established in any observational study.
In light of limited US data currently available for studying educational outcomes associated with GA at term, new prospective studies involving larger, more diverse cohorts are needed. The ability to follow children and reevaluate them at various ages would provide valuable information on the extent of catch-up development and identify interventions that improve outcomes.
The findings from this study highlight the importance of longer gestation, even among term infants, and add to mounting evidence that early term elective deliveries should be avoided. Whereas many organizations suggest waiting until at least 39 weeks to deliver when possible, our findings add to a small group of studies suggesting that GA through 41 weeks is associated with improvements in some educational outcomes.
Dr Hedges contributed to conceptualization and design of the study and analysis and interpretation of the data and drafted the initial manuscript; Dr Reichman contributed to the conceptualization and design of the study and the analysis and interpretation of the data and critically revised the manuscript; Drs Corman and Noonan contributed to the design of the study and analysis and interpretation of the data; and all authors approved the final manuscript as submitted.
Dr Hedges’s current affiliation is Commonwealth Neonatology, Inc, Richmond, Virginia.
FUNDING: This work was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health under award number R01HD090119; the National Center for Advancing Translational Sciences, a component of the National Institutes of Health under award number UL1TR003017; the U.S. Department of Health and Human Services/Health Resources and Service Administration (HRSA) under award number U3DMD32755; and the Robert Wood Johnson Foundation through its support of the Child Health Institute of New Jersey under grant number 74260. The Fragile Families and Child Wellbeing data collection was supported in part by awards R25HD074544, P2CHD058486, and 5R01HD036916 from the Eunice Kennedy Shriver National Institute of Child Health & Human Development. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Eunice Kennedy Shriver National Institute of Child Health & Human Development, National Institutes of Health, HRSA, or the Robert Wood Johnson Foundation.
COMPANION PAPER: A companion to this article can be found online at www.pediatrics.org/cgi/doi/10.1542/peds.2021-051427.
POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose.
FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose.