biomedicines Review Parathyroid Disease in Pregnancy and Lactation: A Narrative Review of the Literature Elena Tsourdi 1, * ,† and Athanasios D. Anastasilakis 2,†   Citation: Tsourdi, E.; Anastasilakis, A.D. Parathyroid Disease in Pregnancy and Lactation: A Narrative Review of the Literature. Biomedicines 2021, 9, 475. https://doi.org/10.3390/ biomedicines9050475 Academic Editor: Roberto Cesareo Received: 13 February 2021 Accepted: 20 April 2021 Published: 26 April 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Center for Healthy Aging, Department of Medicine III, Technische Universität Dresden Medical Center, 01307 Dresden, Germany 2 Department of Endocrinology, 424 General Military Hospital, 56429 Thessaloniki, Greece; a.anastasilakis@gmail.com * Correspondence: elena.tsourdi@uniklinikum-dresden.de; Tel.: +49-351-4581-2933 † These authors contributed equally to this manuscript. Abstract: Pregnancy and lactation are characterized by sophisticated adaptations of calcium home- ostasis, aiming to meet fetal, neonatal, and maternal calcium requirements. Pregnancy is primarily characterized by an enhancement of intestinal calcium absorption, whereas during lactation addi- tional calcium is obtained through resorption from the maternal skeleton, a process which leads to bone loss but is reversible following weaning. These maternal adaptations during pregnancy and lactation may influence or confound the presentation, diagnosis, and management of parathyroid disorders such as primary hyperparathyroidism or hypoparathyroidism. Parathyroid diseases are uncommon in these settings but can be severe when they occur and may affect both maternal and fetal health. This review aims to delineate the changes in calcium physiology that occur with pregnancy and lactation, describe the disorders of calcium and parathyroid physiology that can occur, and outline treatment strategies for these diseases in the above settings. Keywords: hyperparathyroidism; hypoparathyroidism; calcium; pregnancy; lactation 1. Introduction and Methodology Pregnancy and lactation are characterized by profound changes in calcium physiol- ogy, aiming at mineralizing the skeleton of the developing fetus and maintaining calcium homeostasis of the neonate [1,2]. During pregnancy, the fetal demand for this mineral is mainly met through a significant increase in maternal intestinal calcium absorption, which more than doubles. In contrast, during lactation, calcium is derived primarily from the maternal skeleton through the processes of osteoclast-mediated bone resorption and osteocytic osteolysis [2]. These maternal changes during pregnancy and lactation can influ- ence the manifestations, diagnosis, and management of calcium disorders such as primary hyperparathyroidism and hypoparathyroidism [3]. Although they rarely complicate preg- nancy, metabolic bone disorders could have dire consequences for maternal and fetal health. Moreover, it remains currently unknown whether more subtle abnormalities in calcium, vitamin D, and parathyroid hormone levels have clinically important long-term effects on mothers and neonates. In the present review, we aim to briefly review physiological changes in calcium homeostasis during pregnancy and lactation and focus on disorders of calcium and parathyroid physiology, as well as presenting existing treatment approaches. We searched electronic databases (PubMed/MEDLINE) and ClinicalTrials.gov us- ing MeSH terms “Pregnancy”, “Lactation”, “Primary Hyperparathyroidism”, and “Hy- poparathyroidism” up to 28 March 2021. As part of the search for this narrative review, we identified 860 abstracts on PubMed and no clinical trials on ClinicalTrials.gov. After eliminating publications that were not pertinent to the subject of parathyroid and calcium disorders in pregnancy and lactation and duplicates, and extending the literature search by manual searching of the references of selected articles, we retained 100 abstracts on Biomedicines 2021, 9, 475. https://doi.org/10.3390/biomedicines9050475 https://www.mdpi.com/journal/biomedicines