[Recovery of bone mineral density following pregnancy and lactation a longitudinal study]

The purpose of the study was to examine the recovery of maternal bone mineral density (BMD) following pregnancy and lactation, including the effects of subsequent pregnancy and lactation.

Twenty-eight pregnant women were followed longitudinally from early pregnancy (baseline) to five years postpartum (maximum). BMD was measured by ultrasonic bone densitometry at early pregnancy, one week postpartum and at a six-month intervals thereafter. Stiffness calculated from the combined value of speed of sound and broadband ultrasound attenuation was used as an index of BMD. Changes in BMD were examined in 19 women without subsequent pregnancy, divided by the period of lactation, 0-1 month (control), 2-6 months and 8 months or longer. Then, the relationship of recovery of BMD to the interval before a subsequent pregnancy was examined.

1. BMD in women with 0-1 and 2-6 months lactation duration returned to baseline levels within 1 and 1.5 years postpartum, respectively. That in women with a lactation duration of 8-12 months returned to the baseline within 4 years postlivery after an interval of more than 1 year following weaning showed recovery at subsequent delivery. In some, increase was observed after the period of lactation. 3. BMD in women with subsequent delivery within 1 year after weaning showed an overall decrease at subsequent delivery. These results show that BMD lost during pregnancy and lactation returns to the baseline within four years postpartum, depending on the lactation period, and the length of time from weaning to the next delivery, rather than the lactation period, affect BMD recovery.