Parathyroid hormone-related protein (serum)
PTHrP is essential in pregnancy for placental calcium transfer, vasodilation, breast development, and regulation of maternal calcium homeostasis. Levels physiologically rise throughout gestation, especially in the 2nd and 3rd trimesters.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| pmol/L | < 1.3 | 0.7 – 0.9 | 1.8 – 2.2 | 2.5 – 2.8 |
Pregnancy physiology
- PTHrP is produced by placenta, decidua, breast, and fetal tissues.
- Promotes active and passive placental calcium transport.
- Plays a major role in breast development and lactation preparation.
- Contributes to reduced maternal vascular resistance.
Reasons for low PTHrP
- Rarely clinically significant when low in pregnancy.
- May be low in maternal hypocalcemia states.
- Placental insufficiency (theoretical/rare).
- Very low levels may be seen with severe vitamin D deficiency.
Reasons for elevated PTHrP
- Normal pregnancy physiology (most common cause)
- Placental overproduction
- Lactation-associated elevation
- Maternal hypercalcemia
- Hypercalcemia of malignancy (PTHrP–mediated)
- Some ovarian or breast tumors
Markedly elevated PTHrP with hypercalcemia should prompt evaluation for malignancy, though physiologic elevation in pregnancy is typically mild.
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114:1326–31.
- Kovacs CS. Maternal-fetal calcium and bone metabolism during pregnancy, lactation, and post-weaning. Physiol Rev. 2016.
- Fiaschi-Taesch N et al. PTHrP and pregnancy-related calcium physiology. J Endocrinol.