Single Arm Intervention Trial of DEKA TWIIST TM Insulin Pump Utilizing Tidepool Loop Algorithm in Pregnant People With Pre-existing Type 1 Diabetes

Inclusion Criteria: * Singleton pregnancy is confirmed by ultrasound. * Pregnant woman between pregnancy confirmation to 96/7 weeks gestation. * Clinical diagnosis of T1D for 1 year or longer. * Using insulin pump (AID/SAP) or multiple daily insulin injections at screening visit. * Willing to use U100 aspart (Novolog) or lispro (Humalog) insulin during the study. * Willing to announce all carbohydrate intake unless for the treatment or prevention of hypoglycemia. * No significant maternal and/or fetal complications at the time of enrollment visit. * Willing to abide by study protocol. * Willing to learn and use study-provided devices and perform necessary actions for interacting with devices when needed. * Able and willing to receive routine and specialty obstetric care during the study. * Able to speak and understand English and provide informed consent. * Able to have at least one care partner available during the study. A care partner is defined as an adult person (≥18 yrs.) who will either be staying in the same location as the participant or within a 40-mile radius and willing to be trained on study devices and using the TWIIST smartphone App (follower app), will to provide treatment of hypo- and hyperglycemia, and able to take the participant to the hospital or call 911 (emergency services) in case of an emergency. Exclusion Criteria: * Individuals with T2D, gestational diabetes, or other types of diabetes (e.g., CFRD, MODY, etc.). * Use of basal insulin alone. * Use of short-acting insulin alone, unless use is through an insulin pump. * Severe allergy to medical grade adhesives within the last 3 months that would inhibit participant ability to wear the study devices. * Significant maternal and/or fetal complications, such as pre-existing heart disease (untreated or unstable cardiac diseases), pre-existing severe kidney (eGFR \< 45) disease and any other condition that limits participant safety as per investigator discretion. * Unwilling to wear the study insulin pump for the duration of the study or unwilling to switch from current insulin therapy to investigational device for duration of the study. * Presence of significant skin diseases/changes at sensor or infusion wear sites (for example: extensive scarring, extensive eczema, dermatitis herpetiformis, extensive burn or extensive psoriasis). * Multifetal pregnancy. * Inadequate access to a phone and/or computer (for downloading devices and web-based communications). * Unable to attend required on-site study visits due to a planned move to a non-commutable distance to the study site. * People with advanced diabetes complications such as advanced nephropathy (creatinine \>1.5 mg/dl, eGFR \<45 or currently on dialysis), severe autonomic neuropathy, uncontrolled gastroparesis, advanced retinopathy requiring active treatments or as per investigator judgment. * Any bleeding disorder or hemophilia. * Abnormal TSH 6 weeks after two consecutive titrations of thyroid medications * Adrenal insufficiency. * History of severe hypoglycemic event or DKA requiring hospitalization in the past 3 months or greater than 1 episode of DKA within the last year. * Currently being treated for malignancies. * Organ transplant recipient. * On ultra rapid acting insulin, inhaled insulin or U200 insulin unless willing to switch to an insulin with existing data on pump compatibility. * Daily insulin dose ≥ 1.5 units/kg/day at enrollment. * Current use of any non-insulin glucose lowering agents except metformin, unless willing to discontinue use of said agents to participate in the study. * Chronic oral steroid use, current oral steroid use, or high dose steroid use (oral or injectable) in the last 2 months. * Body mass index \> 40 kg/m2 at enrollment. * Known or suspected allergy to insulin. * Severe visual or hearing impairment preventing successful use of study system. * Participant has any condition (physical or psychological disease) that in the opinion of the site investigator would interfere with the normal conduct and interpretation of the study results or put participant at risk during the study. * Currently participating in another pharmaceutical or device related interventional trial at the time of enrollment or any time during the study.