TABLE 1

Characteristics of Study Participants, the Eligible Cohort, and the Full Cohort

CharacteristicStudy Population (n = 599)Invited for the Clinic Visit (n = 2154)Full Cohort (N = 6171)
Child characteristics
 Male sex50.151.651.4
 Age at developmental assessment, mo52.0 ± 5.5
 Plurality
  Singletons52.455.063.3
  Twins43.241.534.5
  Triplets4.33.32.0
  Quadruplets00.20.2
 Gestational age, wk38 (36–39)38 (36–39)38 (36–39)
 Birth weight, g2926 ± 7692932 ± 7993023 ± 752
 Having an older sibling52.251.754.4
 Day care attendance <12 mo59.655.053.6
 Age at achievement of motor milestones, mo
 Sitting without support6.8 ± 1.66.8 ± 1.86.7 ± 1.7
 Standing with assistance8.9 ± 2.18.7 ± 2.18.5 ± 2.0
 Hands-and-knees crawling8.9 ± 2.08.8 ± 2.18.5 ± 2.0
 Standing alone11.3 ± 2.211.3 ± 2.411.0 ± 2.3
 Walking with assistance10.2 ± 2.210.2 ± 2.49.9 ± 2.3
 Walking alone13.0 ± .712.9 ± 5.512.7 ± 4.7
Developmental scale scores
 Adaptive domain22.7 ± 7.2
 Personal/social domain41.0 ± 11.2
 Communication25.2 ± 8.3
 Motor34.1 ± 10.0
 Cognitive35.0 ± 10.6
 Total158.3 ± 39.8
Maternal characteristics
 Age, y32.4 ± 5.531.4 ± 6.030.7 ± 6.0
 Parity, primipara47.448.145.4
 Race/ethnicity
  Non-Hispanic white85.882.980.4
  Not white or other14.217.119.6
 Educational level
  Less than high school2.34.36.0
  High school equivalent6.710.112.5
  Some college25.526.929.9
  College graduate27.424.222.5
  Graduate/professional school38.134.529.1
 Private health insurance86.881.575.8
 Married93.490.988.4
 History of smoking in pregnancy 8.29.813.6
 Alcohol consumption during pregnancy10.911.111.6
 Prepregnancy BMI26.2 (23.0–31.1)25.5 (22.3–30.5)25.5 (22.2–30.6)
 Infertility treatment44.638.432.4
  • Data are presented as mean ± SD for continuous normally distributed variables, median (90% range) for continuous variables with skewed distribution, and percentages for categorical variables. Developmental scale scores were derived by using the BDI-2.