Tresiba while TTC

My wife is TTC and using Tresiba as her basal. She cannot even think to go back on Lantus or Levemir as we have the best A1Cs with Tresiba. Her doctor said that although Tresiba is not approved for pregnancy but she can use it for better control. We are confused what to do… Is there anyone who is using Tresiba in pregnancy? If yes kindly share your experiences.