The immune systems consists of two subsystems, namely the innate and adaptive immune systems. These subsystems work together to defend against foreign pathogens. B cells are one type of cells that is involved in the adaptive immunity. After an encounter with a foreign pathogen, B cells can develop in antibody-producing plasma cells or memory B cells. In pregnant women, a special immunological balance system is set up. The mother needs to be tolerant to the semi-foreign fetus, but the immune system still needs to be effective against potential pathogens. The aim of this study was to track how the memory B cell compartment changes over time in three pregnant women using phylogenetic tree analysis. This was done to understand the immune system in pregnancy more and this knowledge could be used for vaccine development for pregnant women. Immunoglobulin-sequencing data was pre-processed and analyzed. This data included two subsets of memory B cells: CD27bright and CD27dull. Phylogenetic trees were generated with the Dowser tool. Three metrics were also compared between the four time points analysed: Gini inequality coefficient, singletons and normalized tree branch lengths. The results indicate that mainly the CD27bright memory B cells undergo compartmental changes during and after pregnancy. After pregnancy, the CD27bright memory B cells potentially restart from the CD27dull memory B cells. This work was another piece in the immunological puzzle of pregnant women. Further research is needed for the biological relevance of these changes in the memory B cell compartment.