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

BACKGROUND AND OBJECTIVES A worldwide trend towards increasing life ex pectancy has meant that osteoporosis is emerging as an Important publi c health problem. The loss of bone mineral density and its restoration in association with a premenopausal but physiological hypo-oestrogeni c state may serve as an important model for research into the pathogen esis and prevention of osteoporosis. With this in mind we have underta ken a longitudinal study of changes in bone mineral density over one y ear in women after childbirth. DESIGN Observational study of 31 women in the first year following childbirth; 11 intending to breast-feed an d 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 antenat al clinics of the Simpson Memorial Maternity Pavilion. Only nonsmokers who had regular menstrual cycles prior to conception were included. M EASUREMENTS Bone mineral density was measured at the lumbar spine with in 3 weeks of childbirth and repeated at 6 and 12 months post partum. Plasma oestradiol, prolactin and osteocalcin concentrations were measu red 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 firs t 6 months following delivery. This was however reversible since by on e year the bone mineral density was no different from that measured im mediately 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% hi gher than post partum. Artificially feeding women had a steady increas e in bone mineral density in the first year and bone mineral density w as on average 4.3 +/- 1.2% higher. CONCLUSION Breast-feeding results i n a reversible reduction in spinal bone mineral density. The small amo unts 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 furt her study.