Mendelian randomization analysis of 16,349 preeclampsia cases reveals calcium channel blockers (CCBs) reduce preeclampsia risk without harming fetal growth, while beta blockers show no meaningful preeclampsia prevention and are linked to reduced birth weight through direct fetal mechanisms. The study used genetic variants as proxies for drug effects, analyzing over 200,000 births to separate maternal versus fetal genetic influences on outcomes. This genetic approach provides cleaner causal inference than observational studies of actual drug use during pregnancy. The findings challenge current clinical uncertainty about optimal hypertension treatment in pregnancy, where both drug classes are commonly recommended despite limited comparative safety data. CCBs' superior profile—reducing maternal preeclampsia risk while preserving fetal growth—suggests they should be prioritized for pregnancy hypertension management. The direct fetal effects of beta blockers, mediated through ADRB1 receptors, highlight how maternal medications can impact developing fetuses through independent pathways. However, this preprint awaits peer review, and the genetic proxy approach, while innovative, may not fully capture real-world drug effects or dosing considerations. These results warrant validation through randomized trials comparing CCB versus beta blocker strategies for preeclampsia prevention.