Esbach (in his Thèse de Paris, published in 1876) showed that even the finger nails are affected in pregnancy and become measurably thinner.
C. H. Stratz, Die Schönheit des Weiblichen Körpers, Chapter VI.
Iron appears to be liberated in the maternal organism during pregnancy, and Wychgel has shown (Zeitschrift für Geburtshülfe und Gynäkologie, bd. xlvii, Heft II) that the pigment of pregnant women contains iron, and that the amount of iron in the urine is increased.
Vinay, Maladies de la Grossesse, Chapter VIII; K. Hennig, "Exploratio Externa," Comptes-rendus du XIIe. Congrès International de Médècine, vol. vi, Section XIII, pp. 144-166. A bibliography of the literature concerning the physiology of pregnancy, extending to ten pages, is appended by Pinard to his article "Grossesse," Dictionnaire Encyclopédique des Sciences Médicales.