Table of Contents The following summarizes Life Sciences revenues by organizational unit: The Life Sciences segment's revenues in 2019 reflected continued strength in sales of the Preanalytical Systems unit's sales of core products in emerging markets. The Diagnostic Systems unit's 2019 revenues reflected growth in its  BD MAX $^{TM}$ molecular platform as well as growth in sales of core microbiology products. This sales growth in the Diagnostic Systems unit was partially offset by an unfavorable comparison of the unit's U.S. revenues in 2019 to revenues in 2018, as the prior-year period benefited from a more severe influenza season. Revenues in the Biosciences unit in 2019 reflected growth in research reagent sales, as well as growth in U.S. research instrument sales, but were unfavorably impacted by the divestiture of the Advanced Bioprocessing business, as previously discussed. The Biosciences unit's results for 2018 and 2017 included revenues associated with the Advanced Bioprocessing business of $106 million and $103 million, respectively. The Life Sciences segment's 2018 revenues was driven by growth across all three of its organizational units. The Diagnostic Systems unit's revenues were primarily driven by sales of core microbiology products as well as continued strength in sales of the unit's  BD MAX $^{TM}$ molecular platform. Revenue growth in the Diagnostic Systems unit also reflected a more severe influenza season in 2018 compared with 2017. The Life Sciences segment's 2018 revenue growth was also driven by the Biosciences unit's sales of research reagents and recently launched instruments. Growth in the Preanalytical Systems unit reflected global sales of core products. 26 2019 vs. 2018 2018 vs. 2017 (Millions of dollars) 2019 2018 2017 Total Change Estimated FX Impact FXN Change Total Change Estimated FX Impact FXN Change Preanalytical Systems $ 1,558 $ 1,553 $ 1,471 0.3  % (3.0 )% 3.3  % 5.5 % 1.4 % 4.1 % Diagnostic Systems 1,547 1,536 1,378 0.7 % (2.6)% 3.3 % 11.5% 1.9% 9.6% Biosciences 1,194 1,241 1,139 (3.8 )% (2.2 )% (1.6 )% 9.0 % 2.2 % 6.8 % Total Life Sciences revenues $ 4,300 $ 4,330 $ 3,988 (0.7)% (2.6)% 1.9 % 8.6% 1.8% 6.8% Life Sciences Segment • The Medical segment's gross profit margin in 2019 was higher as compared with 2018 primarily due to lower manufacturing costs resulting from continuous improvement projects which enhanced the efficiency of our operations. Additionally, the comparison of gross profit margin in 2019 with gross profit margin in 2018 reflected the unfavorable impacts in 2018 of a fair value step-up adjustment relating to Bard's inventory on the acquisition date and charges to write down the value of fixed assets, primarily in the Diabetes Care unit. These favorable impacts to the Medical segment's gross margin in 2019 were partially offset by unfavorable foreign currency translation, higher raw material costs and pricing pressures. The Medical segment's gross profit margin in 2018 was lower as compared with 2017 primarily due to the expense related to amortization of intangible assets acquired in the Bard transaction as well as the impact of the fair value step-up adjustment and write- down charges noted above. The Medical segment's gross profit margin in 2018 was also unfavorably impacted by higher raw material costs and pricing pressures. These unfavorable impacts to the Medical segment's gross margin were partially offset by lower manufacturing costs resulting from continuous improvement projects which enhanced the efficiency of our operations and favorable product mix impact relating to the Bard products reported within the segment. • Selling and administrative expense as a percentage of revenues in 2019 was relatively flat compared with 2018. Selling and administrative expense as a percentage of revenues in 2018 was lower compared with 2017 which primarily reflected a reduction in the general and administrative costs allocated to the segment, as noted above. • Research and development expense as a percentage of revenues was lower in 2019 due to recent completion of projects and the timing of project spending. Research and development expense as a percentage of revenues in 2018 was higher compared with 2017 which reflected increased investment in new products and platforms.