ORAL PROGESTOGEN-ONLY CONTRACEPTION MAY PROTECT AGAINST LOSS OF BONE MASS IN BREAST-FEEDING WOMEN

BACKGROUND AND OBJECTIVES A worldwide trend towards increasing life expectancy has meant that osteoporosis is emerging as an Important public health problem. The loss of bone mineral density and its restoration in association with a premenopausal but physiological hypo-oestrogenic state may serve as an important model for research into the pathogenesis and prevention of osteoporosis. With this in mind we have undertaken a longitudinal study of changes in bone mineral density over one year in women after childbirth. DESIGN Observational study of 31 women in the first year following childbirth; 11 intending to breast-feed and use barrier methods of contraception, 9 intending to breastfeed and to use the progestogen-only pill and 10 intending to artificially feed and to use barrier methods. PATIENTS Recruitment was from the antenatal clinics of the Simpson Memorial Maternity Pavilion. Only nonsmokers who had regular menstrual cycles prior to conception were included. MEASUREMENTS Bone mineral density was measured at the lumbar spine within 3 weeks of childbirth and repeated at 6 and 12 months post partum. Plasma oestradiol, prolactin and osteocalcin concentrations were measured at each visit, RESULTS Breast-feeding women using barrier methods lost a mean +/- SE of 4.9 +/- 1.5% of bone mineral density in the first 6 months following delivery. This was however reversible since by one year the bone mineral density was no different from that measured immediately post partum. Breast-feeding women using the progestogen-only pill lost a significantly smaller percentage of bone mineral density in 6 months and by one year bone mineral density was 2.95 +/- 0.75% higher than post partum. Artificially feeding women had a steady increase in bone mineral density in the first year and bone mineral density was on average 4.3 +/- 1.2% higher. CONCLUSION Breast-feeding results in a reversible reduction in spinal bone mineral density. The small amounts of gestagen in the progesterone-only pill would appear to protect against this loss. The mechanism of this loss In bone mineral density and the potentially bone protective effects of gestagens require further study.