Table 2.
Changes in calcium homeostasis during pregnancy and lactation
| Measured levels | Pregnant woman | Placenta | Fetus | Lactating woman |
|---|---|---|---|---|
| Serum Ca |
Total Ca ↓ Ionized Ca↔ Intestinal absorption twofold ↑ |
Active transfer dependent on PTHrP + passive transfer |
Higher than maternal levels; regulated by fetal PTHrP |
Ionized Ca slightly ↑ Bone resorption ↑ |
| Urinary Ca | ↑ | Unknown | ↔ | |
| PTH | ↓↔ | No transfer | Low | Low |
| PTHrP | Progressively ↑ secretion by decidua and breasts | No transfer; placental and amniotic secretion |
Higher than in mother Secretion by the umbilical cord and fetal parathyroid glands as early as 10 weeks |
↑↑: secretion by breasts |
| 25‐vitamin D | ↔ | Transfer; placental hydroxylation | Renal hydroxylation | ↔ |
| 1,25‐dihydroxyvitamin D | Progressive ↑ by 100%; calbindin‐D9k ↑ | No transfer | Low | ↔ |
| 1α‐hydroxylase activity |
↑ Stimulated by estradiol, prolactin, placental lactogen, PTHrP |
Present | Present in the kidney | ↔ |
| Calcitonin |
↑ by 20% Secretion by thyroid and breasts |
No transfer; placental secretion | ↑ in the first 6 weeks |