Strict blood sugar control can reduce pregnancy related complications in women with T1D. The Tandem t:slim X2 closed-loop system is a new technology that uses a continuous glucose monitor, insulin pump, and computer algorithm (Control IQ) to deliver insulin. The purpose of this study is to see if the Tandem t:slim X2 with Control IQ improves blood sugar control, reduces episodes of low blood sugar, decreases burden of diabetes self-care and partner distress, and results in healthier pregnancies.