hCG Urinary Metabolites in Breast Milk

Introduction

Human chorionic gonadotropin (hCG) is the glycoprotein hormone associated with the onset of pregnancy. The molecule can be detected in maternal serum and urine following implantation [1], and assays for hCG have been used to detect and monitor pregnancy for over 70 years [2] [3]. During pregnancy, hCG has also been detected in saliva [4] [5]. hCG is a heterodimer consisting of two subunits, α and β, held together non-covalently. Dissociation of the α and β subunits initiates the metabolism of hCG and results in the terminal hCG breakdown product β-core fragment (hCGβcf), which is found in renal tissue only [6] [7] [8] and is present at high concentrations in urine samples [8] [9] [10] [11] [12] [13] [14] [15]. Since hCGβcf is hardly detectable in serum, it is generally assumed that the kidney is the major breakdown site of hCG metabolism.

Breast-feeding can provide protection against pregnancy for up to six months postpartum [16]. During breastfeeding, prolactin mediates the cessation of menses by suppressing pituitary LH and FSH [17], and it is therefore quite uncommon for a breast-feeding mother to become pregnant. This is the likely reason why there have been no previous investigations on hCG in breast milk in pregnant breastfeeding mothers. To examine the metabolism of hCG, we investigated the concentrations of intact hCG (hCG), hCG free beta subunit (hCGβ), nicked hCG cleaved at p47 - 48 (N-hCG), hCGβcf, and hyperglycosylated hCG (H-hCG) in the serum, urine, saliva, and breast milk of a lactating pregnant woman.

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