A prospective study of calciotropic hormones in pregnancy and post partum: reciprocal changes in serum intact parathyroid hormone and 1,25-dihydroxyvitamin D.
OBJECTIVE
The purpose of this study was to examine the hormones regulating calcium homeostasis longitudinally in pregnancy and post partum.


METHODS
Twenty-three women with normal pregnancies were studied in the second and third trimesters and post partum. At each time blood was analyzed for ionized calcium, vitamin D metabolites, and intact parathyroid hormone, and a 24-hour urine specimen was analyzed for creatinine, calcium, and sodium.


RESULTS
Urinary calcium excretion was 250% to 300% higher during pregnancy than post partum (p < 0.00001). 1,25-Dihydroxyvitamin D levels were equivalent in the second and third trimesters but were twofold higher than postpartum values (p < 0.01). Ionized calcium was similar at all time points. Intact parathyroid hormone in the second and third trimesters was 50% of postpartum levels (p < 0.001).


CONCLUSIONS
Pregnancy is associated with an increase in the levels of 1,25-dihydroxyvitamin D and a concomitant reciprocal fall in intact parathyroid hormone levels. The increase in serum 1,25-dihydroxyvitamin D values appears to be a key factor in providing for the increase in maternal calcium requirements during pregnancy.
Seely
E W
EW
Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA.
Brown
E M
EM
DeMaggio
D M
DM
Weldon
D K
DK
Graves
S W
SW
D000328:Adult; D002118:Calcium / Q000378:metabolism; D005260:Female; D006706:Homeostasis; D006801:Humans; D010281:Parathyroid Hormone / Q000097:blood*; D049590:Postpartum Period / Q000097:blood*; D011247:Pregnancy / Q000097:blood*; D011446:Prospective Studies; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
D010281:Parathyroid Hormone; D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D; D002118:Calcium