This is a prospective observational trial of healthy postpartum women to investigate changes in bone density and markers of bone turnover during lactation. The study hypothesis is that women who breast-feed 5 months or more will lose bone density and subsequently regain the bone density after weaning. This study seeks to define determinants of the regain in bone density.

This is a prospective observational trial enrolling healthy postpartum women, ages 20 years and older with the intent to breast-feed from the UNC outpatient obstetrical clinics and the UVA outpatient obstetrical clinics. These women were studied at 3-5 visits in the year following their delivery to assess bone density, nutritional intake, exercise, and breast-feeding choices. The number of study visits depended on the timing of return of menses and interest in participating in the follow-up study (timepoints are: immediate postpartum, 3 months postpartum, return of menses, 6 months after return of menses and follow-up visit 6 months after final visit). Blood was taken for analysis of bone-related hormones, bone turnover and calcium homeostasis markers. The study focuses on women with extended lactation (at least 5 months of lactation) whereas women who cease lactation prior to 3 months will be the primary comparison group.

Inclusion Criteria:

• age >20 at the time of delivery
• singleton pregnancy and
• <2 prior pregnancies that were >20 weeks gestation.

Exclusion criteria:

• maternal rheumatologic disorders
• maternal anorexia nervosa
• maternal endocrinologic disorders,
• medications known to affect bone density such as corticosteroids, thyroid hormone use, anticonvulsant therapy, bisphosphonates, long-term GnRH agonists use and calcitonin.
• Subsequent pregnancy during the study

Postpartum women from outpatient obstetrical/gynecology clinics.

Deidentified IPD may be available by direct request of Principal Investigator.