2) 118.4 (3.9) Sex (%) Male 7,121 (100.0) 49.6 Female   50.4 Height (cm) 7,047 (99.0) 139.5 (6.3) Weight (kg) 7,105 (99.8) 33.2 (29.4–38.4)a TBLH

BMC (g) 6,775 (95.1) 893.8 (184.0) TBLH BA (cm2) 6,775 (95.1) 1139.5 (164.3) TBLH BMD (g/cm2) 6,775 (95.1) 0.78 (0.05) TBLH ABMC 6,775 (95.1) 894.6 (39.8) Spine BMC (g) 5,487 (77.1) 78.4 (15.7) Spine BA (cm2) 5,487 (77.1) 100.7 (12.0) Spine BMD (g/cm2) 5,487 (77.1) 0.77 (0.08) Spine ABMC (g) 5,487 (77.1) 78.4 (7.1) Pubertal stage (%) Boys Tanner 1 2,365 (67.0) this website 82.9 Tanner 2   16.5 Tanner 3+   0.6 Girls Tanner 1 2,836 (79.0) 81.5 Tanner 2   15.0 Tanner 3+   3.5 Age at menarche for girls (years) (%) Up to 10 3,107 (86.5) 4.7 11+   95.3 Gestational age (weeks) 7,121 (100.0) 39.5 (1.8) Birth weight (kg) 7,035 (98.8) 3.4 (0.5) Household social class (%) I 6,544 (91.9) 15.5 II   45.1 III NM   24.8 III M   10.3 IV/V   4.3 Mother Age at delivery (years) 7121 (100.0) 29.0 (4.6) Height (cm) 6753 (94.8) 164.1 (6.6) Pre-pregnancy BMI (kg/m2) 6429 (90.3) 22.2 (20.5–24.4)a No. of previous births (%) 0 6879 (96.6) 45.8 1   35.5 2   13.7 3   3.8 4 or more   1.2 Smoking during pregnancy (%) Never 6379 (89.6) 78.7 1 or 2 trimesters   9.5 All trimesters   11.8 Education (%) None/CSE 6860 (96.3) 13.8 Vocational   8.5 O Levels   35.2 A Levels   26.6 Degree   15.8 Father IWR-1 nmr Age at child’s

birth (years) 5106 (71.7) 31.4 (5.2) Height (cm) 4931 (69.2) 176.3 (6.9) BMI (kg/m2) 4887 (68.6) 24.8 (22.9–26.9)a Regular smoker (%) No 6679 (93.8) 65.3 Yes   34.7 Education (%) None/CSE 6467 (90.8) 19.3

Vocational   8.2 O Levels   21.7 A Levels   28.5 Degree   22.2 ABMC area-adjusted bone mineral content, BA bone area, BMC bone mineral content, BMD bone mineral density, BMI body mass index, IQR interquartile Protein tyrosine phosphatase range, TBLH total body less head aMedian and interquartile range are shown for skewed variables Pairwise correlations of total body and spinal bone measures are given in ESM Web Table 3, and correlations of these measures with child and parental characteristics are shown in ESM Web Table 4. Mean differences in TBLH BMC and BA were slightly higher for mTOR inhibitor mothers who smoked in all trimesters of pregnancy, but other associations were similar. In boys, maternal smoking in any trimester was not robustly associated with any TBLH or spinal bone outcomes. P values for sex differences were 0.007, 0.003 and 0.085 for TBLH BMC, BA and BMD and 0.036, 0.035 and 0.