A model for the transfer of calcium and strontium to the fetus

A biokinetic model has been developed for the transfer of calcium and strontium to the human fetus. For the mother, ICRP models were adapted for pregnancy to include increases in gastrointestinal absorption, urinary excretion and bone turnover rates. The fetus was modelled with blood, soft tissue and bone compartments. Fetal requirements for Ca were determined by skeletal calcification and recycling between fetal and maternal blood was included. Daily transfer of Sr to the fetus was taken to be 0.6 times that of Ca. For acute intakes of ⁴⁵Ca and ⁹⁰Sr in late pregnancy at 36 weeks after conception, when maximum transfer occurs, the model predicts C(F):C(M) ratios of 19 and 9, respectively. Corresponding committed doses to the red bone marrow offspring would be greater than in adults by factors of about nine for ⁴⁵Ca and about two for ⁹⁰Sr.