It's been recognized for quite a while that the symptoms of autoimmune diseases decrease during pregnancy.
Here's one of the stardard ways to draw images of vitamin D and two steroid hormone molecules in Organic Chemistry. The vertices in these drawings represent carbon atoms in single or double covalent bonds. Double bonds share two pairs of electrons and are indicated by a pair of parallel lines. Single covalent bonds of carbon to hydrogen at the vertices is assumed as the convention. C represents carbon, O represents oxygen and H represents hydrogen.
In the second drawing, C23H28O6 is another way to describe the molecule which has a molecular wieght of 400.47 units, of average atomic wieght units when the average weight and distribution of isotopes are included. The subscripts indicate the total number of each elements number of atoms in the molecule.
vitamin D3 from http://bioe.eng.utoledo.edu/adms_staffs/akkus/2003_WEB_PROJECTS/hormone/vitamin_d.htm
prednisone from http://img.alibaba.com/photo/50457579/Prednisone_Acetate.jpg
from http://www-klinik.uni-mainz.de/Zentrallabor/Lab-Web/Hypertextbook/cortisol.gif
The money quote is at the end of the first paragraph on page 11: "But that's the difference between Vitamin D and prednisone, that one bond."