group as in the early preterm group, we recruited a randomly
selected sample of individuals born late preterm from the
FMBR. From both cohorts, we recruited a group of randomly
selected controls (Figure 1). Because of slight variation in
number of individuals recruited through the cohorts, we adjusted
for recruitment cohort (NFBC or FMBR) in all the
analyses.
In 2009–2011, a total of 779 individuals participated in a
clinical study. After verification of the length of gestation from
medical records (15),we excluded 2 participants whose length
of gestation could not be verified and 27 subjects thought to
be born preterm who were actually born at term (Web Table 1
available at http://aje.oxfordjournals.org/). Those who were
pregnant (n = 18) or who reported having cerebral palsy (n =
6), a mental disability (n = 7), and/or another severe physical
disability (n = 3) were excluded from analysis because these
conditions might affect the main outcomes. Three subjects
had more than 1 criterion for exclusion. In addition, 7 subjects
reported the use of β-blockers for indications other than
hypertension, and they were excluded from the blood pressure
analysis. Thus, there were 134 participants who were
born early preterm, 242 participants who were born late preterm
(16), and 344 controls who were born at term. The perinatal
data are shown in Table 1.
We compared persons who participated with those who
did not or who were excluded from the analysis because
of pregnancy or physical disability. This comparison was
based on perinatal data from the NFBC database (participants
from NFBC) and the FMBR (participants born between
1987 and 1989). In addition, we compared the results
of the clinical examinations that took place at 16 years of
age among those NFBC members who had participated in
that examination. The comparative data are shown in Web
Table 2.