Hyperemesis Gravidarum Risk Reduction With Metformin

Inclusion Criteria: * Ages 18-49 * HG in prior pregnancy (clinical criteria: intravenous (IV) fluid treatment) * Trying to conceive * Treatment Arm: willing to refrain from trying to conceive during their metformin dose titration period and before 2 weeks at maximum tolerated dose (up to 8 weeks total). Will use birth control or contraceptive device until maintenance dose. * Under care of a personal OB/GYN or willing to establish care with a personal OB/GYN before study start * Ownership of a personal scale (or willingness to obtain one for study use) * Willing to participate in a trial that includes daily use of an oral agent prior to pregnancy * Treatment Arm: residing in California/Alabama * Treatment Arm: normal blood panel (CBC) (e.g., white count, hemoglobin, platelets all within the normal range) * Treatment Arm: normal to mildly decreased creatinine levels (estimated GFR \> 60 mL/min/1.73m²) * Survey/Comparator Arm: not currently taking metformin and do not plan to take metformin prior to pregnancy * Able and willing to provide written informed consent prior to initiation of any study procedures. * Demonstrates understanding of the study objectives, requirements, potential risks, and willingness to comply with study procedures and follow-up. * English speaking * Regular cycles Exclusion Criteria: * Allergic or adverse reaction to metformin-XR * Thalassemia * Cirrhosis and/or hepatic impairment * Decompensated heart failure * Daily/regular use of medications/substances (tobacco, cyclobenzaprine, cannabis, escitalopram, sertraline, other SSRIs, Lasix) * Treatment Arm: Use of insulin, sulfonylureas, meglitinides, or other blood sugar altering medication * Assisted Reproductive Technology * Excess alcohol consumption (\> 7 standard drinks per week on average) * Pregnant * Not trying to conceive * Treatment Arm: Residing outside California/Alabama * Treatment Arm: abnormal blood panel (CBC) (e.g., white count or platelets not within the normal range) * Treatment Arm: abnormal creatinine levels (estimated GFR \< 60 mL/min/1.73m² excluded from the study, signs of kidney disease) * Treatment Arm: current metformin use * Survey/Comparator Arm: current metformin use or plans to take metformin prior to pregnancy * Any medical/surgical condition that the investigator feels would compromise the participant's participation in the study * Not able and willing to provide written informed consent prior to initiation of any study procedures. * Does not demonstrate understanding of the study objectives, requirements, potential risks, and willingness to comply with study procedures and follow-up. * Not english speaking * Irregular cycles * Not willing to refrain from trying to conceive/use birth control or contraceptive device until maintenance dose.