Research Study Comparing Insulin Degludec to Insulin Detemir, Together With Insulin Aspart, in Pregnant Women With Type 1 Diabetes

The investigators are doing this study to see the effect of insulin degludec in pregnant women with type 1 diabetes, and if it is safe to use. In this study the medicine insulin degludec is compared to another medicine called insulin detemir. Participants will either get insulin degludec or insulin detemir and take it together with a medicine called insulin aspart - which treatment participants get is decided by chance. Participants will get pre-filled insulin pens. Participants will need to take blood sugar measurements several times a day. The study will last between 10 and 25 months depending on whether participants are already pregnant when they join the study. The number of visits and the tests ( for example blood and urine samples and ultrasound scans) the participants will have also depends on whether they are pregnant at study start.

Inclusion Criteria: - Female, age at least 18 years at the time of signing informed consent - Diagnosed with type 1 diabetes mellitus for at least 1 year prior to the day of screening - Treated with multiple daily subcutaneous insulin injections or continuous subcutaneous insulin infusion (CSII) or inhaled insulin for at least 90 days prior to the day of screening - The subject is planning to become pregnant within 12 months from randomisation and willing to undertake pre-pregnancy counselling or the subject is pregnant with an intrauterine singleton living foetus (gestational week 8 to 13 (+6 days)) without any observed anomalies at randomisation, confirmed by an ultrasound scan - HbA1c at screening below or equal to 8.0% (64 mmol/mol) by central laboratory Exclusion Criteria: - Treatment with any medication for the indication of diabetes or obesity other than stated in the inclusion criteria within the past 90 days prior to the day of screening - Pregnant and having proteinuria as evaluated by urine protein-to-creatinine ratio above or equal to 300 mg/g in urine sample measured at screening - Subject being treated or became pregnant with assistance of in vitro fertilisation or other medical infertility treatment - Receipt of any concomitant medication contraindicated in pregnancy according to local label within 28 days before screening and between screening and randomisation for non-pregnant subjects and 28 days before conception and between conception and randomisation for pregnant subjects - Proliferative retinopathy or maculopathy requiring acute treatment. Verified by fundus photography or pharmacologically dilated fundoscopy performed within the past 90 days prior to randomisation for non-pregnant subjects or within 28 days prior to randomisation for pregnant subjects. - History of severe hyperemesis gravidarum (requiring hospitalisation)