Table 1.
Puberty Measures, Dual-Energy x-Ray Absorptiometry Percent Body Fat and Bone Mass Measurements, and Magnetic Resonance Imaging Breast Tissue Composition of Singleton Nulliparous Women (n = 500) From the Avon Longitudinal Study of Parents and Children, 1991–2014
| Variable | No. of Women | % | Mean (SD) | Median (IQR) |
|---|---|---|---|---|
| Puberty variables | ||||
| Age at menarche, years | 469 | 12.7 (1.0) | 12.7 (12.0–13.3) | |
| Age at thelarche, yearsa | 486 | 10.4 (1.4) | 10.2 (9.0–11.2) | |
| Age at completion of breast development, yearsa | 451 | 13.1 (1.6) | 12.7 (12.4–13.9) | |
| Duration of breast development, yearsa | 426 | 2.9 (1.4) | 2.7 (2.0–3.7) | |
| DXA measuresb | ||||
| Age at DXA measurement, years | ||||
| 9 | 449 | 9.8 (0.3) | 9.8 (9.7–9.9) | |
| 11 | 461 | 11.7 (0.2) | 11.7 (11.6–11.8) | |
| 13.5 | 443 | 13.8 (0.2) | 13.8 (13.7–13.9) | |
| 15.5 | 423 | 15.4 (0.2) | 15.3 (15.3–15.5) | |
| DXA body fat mass, % | ||||
| At age 9 years | 447 | 26.0 (8.2) | 25.3 (19.7–31.0) | |
| At age 11 years | 460 | 27.2 (8.2) | 26.7 (21.3–32.7) | |
| At age 13.5 years | 443 | 28.2 (8.0) | 27.9 (21.7–33.6) | |
| At age 15.5 years | 428 | 30.0 (7.8) | 29.1 (24.3–35.8) | |
| DXA body bone mass, % | ||||
| At age 9 years | 447 | 3.5 (0.4) | 3.6 (3.3–3.8) | |
| At age 11 years | 460 | 3.7 (0.4) | 3.7 (3.4–4.0) | |
| At age 13.5 years | 443 | 4.0 (0.4) | 4.0 (3.7–4.3) | |
| At age 15.5 years | 428 | 4.2 (0.4) | 4.2 (3.9–4.4) | |
| Characteristics at MRI examination | ||||
| Age, months | 491 | 257.9 (11.0) | 259.0 (251.0–265.0) | |
| Menstrual phasec | ||||
| Follicular | 70 | 14 | ||
| Luteal | 50 | 10 | ||
| Taking hormonal contraceptives | 339 | 70 | ||
| Irregular menstrual period | 28 | 6 | ||
| MRI breast measuresd | ||||
| Left-right average breast volume, cm3 | 490 | 647.2 (461.1) | 507.8 (320.6–789.8) | |
| Left-right average breast fat volume, cm3 | 490 | 406.3 (349.5) | 292.2 (166.7–494.6) | |
| Left-right average breast water volume, cm3 | 490 | 240.9 (131.2) | 209.8 (144.3–316.7) | |
| Left-right average breast percent water | 491 | 41.8 (10.3) | 41.7 (33.7–49.7) |
Abbreviations: DXA, dual-energy x-ray absorptiometry; IQR, interquartile range; MRI, magnetic resonance imaging; SD, standard deviation.
a Age at thelarche and age at completion of breast development were estimated as described in the Methods section. Duration of breast development was estimated as age at breast development completion minus age at thelarche.
b DXA percent body bone and fat masses were estimated as described in the Methods section.
c Estimated for women who were not taking hormonal contraceptives at the time of the MRI by calculating the number of days since the last menstrual period (date of MRI minus starting date of last menstrual period). Luteal phase (days 14–17 to 28–31), follicular phase (days 0 to 14–17), and “irregular menstrual period” (≥32 days) were defined using self-reported average length of the menstrual cycle.
d Sections of the breast were missing in the MRI images for 1 participant. Hence, for that participant, percent water could be estimated from the available MRI images, but absolute volumetric measurements (i.e., breast, fat, and water volumes) could not.