It is well-known that regular physical activity (PA) can improve glycemic control and physical fitness in type 2 diabetes patients. However, studies examining the effects of PA in patients with gestational diabetes mellitus (GDM) are limited. Interval walking training (IWT) is a careful type of PA consisting of repeatedly cycles of 3 min. fast and slow walking. The investigators aimed to examine, if IWT is feasible as PA intervention for GDM patients, and to examine the effects of IWT on glycemic control, PA levels and physical fitness.

Gestational diabetes mellitus (GDM), defined as glucose intolerance and thus hyperglycemia with onset or first recognition during pregnancy, is steadily increasing in prevalence. In Denmark, the prevalence of GDM is around 2-3% of all pregnancies. GDM is associated with several adverse perinatal and maternal outcomes why early recognition and diagnosis is important. Early diagnosis and relevant treatment can prevent adverse outcomes of the baby and mother, such as macrosomia, shoulder dystocia, preeclampsia and hypoglycemia.

The glucose levels will often normalize shortly after birth; however, up to 50% of all women in Denmark diagnosed with GDM develop T2D during the first 10 years after the pregnancy, have a threefold risk of developing metabolic syndrome2 10, while the recurrence risk of developing GDM in subsequent pregnancies varies between 30-84%. Furthermore, long term increased risks for children born with macrosomia or by a mother with GDM include cardiovascular disease, obesity and T2D.

Glycemic control is a key factor in combatting the severe effects related to poorly controlled GDM. Management of GDM in Denmark consists of regular BG self-monitoring, dietary modifications, and in some cases insulin treatment. Additionally, obstetric control visits and PA advices are also a part of the standard GDM care program.

Compared to non-pregnant women, pregnant women must be more careful in relation to especially the type of PA, why supervised exercise is often recommended in order to ensure safe and correct guidance. This is a heavy economic burden, why a structured, non-supervised type of PA with low a risk of injury, possibly high compliance and continuous monitoring would be preferable. Interval walking training (IWT) is a lenient type of structured, non-supervised PA. This type of PA is associated with an improved glucose regulation in patients with T2D after 4 months of IWT 5 times weekly (60 min./session) (Karstoft et al., 2013). Due to similar metabolic dysregulations in patients with T2D and GDM, the investigators are apt to believe that IWT, if feasible, can improve glycemic control in GDM patients. Furthermore, it is obvious to believe that IWT can be implemented as regular PA in GDM patients, as one study has shown that pregnant women mostly prefer walking as a type of PA during pregnancy.

This open-label randomized controlled trial aims to enroll 20 patients randomized (1:1) to a control- (Con) or IWT-group. Both groups will follow the standard GDM care program at Odense University Hospital. Additionally, the IWT-group is prescribed three weekly IWT sessions of 40-50 minutes each for 6 weeks. Each IWT session is guided and controlled by the smartphone application 'InterWalk', which individualize the training intensity to current fitness level of the patient through an on-board fitness test.

Inclusion Criteria:

• Diagnosed with GDM by a 2 hour oral glucose tolerance test with a BG level of >9.00mmol/l at 2 hours
• Danish speaking
• >18 years of age
• Live <20 kilometers from Odense city center

Exclusion Criteria:

• Pelvic pains
• Untreated depression
• Walking disabilities
• Pregnancy-related complications
• >32 weeks

As only women can be diagnosed with gestational diabetes mellitus, only women are eligible in participating in the study.