Baseline characteristics of infants who were normal, had colic, or had prolonged crying
| Normal (n = 264) | Colic (n = 48) | PC (n = 15) | ||||
|---|---|---|---|---|---|---|
| Data are n (%) or mean (SD). | ||||||
| *Total family income per month in US dollars at an exchange rate of approximately 1 Norwegian Kroner = 0.1382 US$. | ||||||
| †p<0.05. | ||||||
| ‡Months’ leave between delivery and returning to part-time or full time employment; data apply only to women who returned to work (162, 22, and 8 mothers, respectively). | ||||||
| §Maternal intelligence quotient (IQ) using Raven’s progressive matrices (raw score out of a maximum of 60); measurements were available on 209, 38, and 13 mothers, respectively. | ||||||
| ¶Home screening questionnaire scores (raw score of a maximum of 43); measurements available at the Norwegian sites on 150, 30, and 9 homes, respectively. | ||||||
| **Admitted to neonatal intensive care unit (NICU) at birth. | ||||||
| ††Ferritin concentrations (µg/l) in cord blood. | ||||||
| NICU, neonatal intensive care unit; PC, prolonged crying. | ||||||
| Site of enrolment | ||||||
| Uppsala | 96 (36%) | 16 (33%) | 5 (33%) | |||
| Bergen | 90 (34%) | 13 (27%) | 6 (40%) | |||
| Trondheim | 78 (30%) | 19 (40%) | 4 (27%) | |||
| Family income (US$)* | 3745 (1521) | 3844 (1177) | 4008 (1308) | |||
| Maternal characteristics | ||||||
| Maternal age (years) | 29.6 (3.9) | 29.9 (4.0) | 32.0 (5.2)† | |||
| Maternity leave‡ | 8.7 (3.6) | 9.6 (3.5) | 10.6 (4.0) | |||
| Parity 1 | 181 (69%) | 34 (71%) | 10 (67%) | |||
| Parity 2 | 83 (31%) | 14 (29%) | 5 (33%) | |||
| Education | ||||||
| <10 years | 42 (16%) | 4 (9%) | 1 (7%) | |||
| 10–11 years | 72 (27%) | 13 (28%) | 4 (27%) | |||
| High school | 62 (24%) | 11 (23%) | 2 (13%) | |||
| Trade school | 67 (25%) | 16 (34%) | 5 (33%) | |||
| University | 20 (8%) | 3 (6%) | 3 (20%) | |||
| Maternal IQ§ | 48.9 (6.3) | 48.2 (7.1) | 48.5 (10.1) | |||
| Smoker (conception) | 90 (34%) | 22 (46%) | 3 (20%) | |||
| Body mass index (kg/m2) | 21.9 (2.8) | 22.2 (2.9) | 21.9 (2.3) | |||
| Home screening score¶ | 35.4 (2.9) | 35.2 (2.9) | 36.0 (2.9) | |||
| Infant characteristics | ||||||
| Male | 127 (48%) | 24 (50%) | 5 (33%) | |||
| Admitted to NICU** | 14 (5%) | 1 (2%) | 0 (0%) | |||
| Serum ferritin (µg/l)†† | 156 (97) | 152 (85) | 164 (112) | |||
| Birth weight (g) | 3705 (512) | 3617 (594) | 3597 (468) | |||
| Head circumference (cm) | 35.4 (1.2) | 35.2 (1.3) | 34.9 (1.2) | |||
| Ponderal index (g/cm3) | 2.77 (0.25) | 2.79 (0.21) | 2.70 (0.21) | |||
| 5 min Apgar score ⩾8 | 254 (97%) | 47 (100%) | 15 (100%) | |||
| Attended kindergarten | 197 (77%) | 39 (85%) | 12 (86%) | |||
| Exclusively breast fed (weeks) | 13.9 (7.5) | 12.2 (7.7) | 12.8 (7.3) | |||
| Any breast feeding (weeks) | 28.2 (14.8) | 28.1 (16.2) | 29.7 (14.6) | |||