KCCO - here is the Tresiba label https://www.accessdata.fda.gov/drugsatfda_docs/label/2015/203314lbl.pdf
It says There are no well-controlled clinical studies of the use of insulin degludec in pregnant women.
Patients should be advised to discuss with their health care provider if they intend to or if they become pregnant
It goes on to say Subcutaneous reproduction and teratology studies have been performed with insulin degludec and human insulin (NPH) as a comparator in rats and rabbits. In these studies, insulin was given to female rats before mating throughout pregnancy until weaning, and to rabbits during organogenesis. The effect of insulin degludec was consistent with those observed with human insulin…
Here is what Levimir’s label says - Pregnancy - The effect of pregnancy on the pharmacokinetics and pharmacodynamics of LEVEMIR has not been studied (see PRECAUTIONS, Pregnancy)
With Levimir the rat and rabbit embryofetal development studies that included concurrent human insulin control groups indicated that insulin detemir and human insulin had similar effects regarding
embryotoxicity and teratogenicity
Tresiba and Levimir basically have the same label when it comes to pregnancy. I am not sure why you are being told to switch. Levimir has no advantage per the label for pregnancy.