Time to Move in Pregnancy Hyperglycemia

This randomized controlled crossover trial of 36 pregnant individuals with gestational diabetes (GDM) or gestational glucose intolerance (GGI) will:

1. Determine the effects of physical activity (PA) timing, specifically 30 minutes of moderate intensity walking or stepping in the morning (between 5am-9am, within 30-40 minutes of starting breakfast), versus late afternoon/evening (between 4pm-8pm, within 30-40 minutes of dinner) on glucose across the 24-hour cycle.
2. Explore the potential effects of the timing of PA on sleep and mood state.

Research participants will:

1. Exercise according to a schedule provided by the study for an 11-day period. They will complete either no exercise or 30 minutes of walking/stepping (e.g., stepping in place or around the house when walking outside is not an option or not an attractive option) on specifically assigned days, at specifically assigned times of day.
2. Wear a masked Dexcom G6 continuous glucose monitor (CGM) or unmasked Dexcom G7 CGM for the 11-day study period.
3. Wear a masked physical activity (PA) monitor watch (ActiGraph CentrePoint Insight Watch) on the non-dominant wrist for the 11-day study period (all day and all night).
4. Take pictures of all of food and drinks consumed, at the start and end (showing food and drink not eaten) of all eating occasions. Participants will use their phones to upload photos to a study website for the entire 11-day study period. Participants will also complete 24-hour dietary recall phone calls for 3 of the 11 study days (i.e., for 1 morning PA day, 1 late afternoon/evening PA day, and 1 no PA day, with the days randomly selected).
5. Complete electronic REDCap surveys, including daily surveys that assess: when (i.e., the exact times) they started eating breakfast, lunch, and dinner that day; when (e.g., the exact times) they went to bed and fell asleep for the night and woke up and got out of bed the next morning, and questions on the quality of their sleep; adverse events and issues with the study equipment (e.g., CGM); and mood state following PA (on days assigned 30 minutes of walking/stepping).

Eligibility Criteria:
Eligibility Criteria

* Singleton, viable pregnancy with low suspicion for clinically significant abnormality or aneuploidy
* Age 18-40 years (at recruitment)
* Comfortable communicating with study staff in English and completing study surveys in English (i.e., no translator needed)
* Identified as Gestational Glucose Intolerance (GGI) and a 3-hr 100g OGTT for Gestational Diabetes Mellitus (GDM) performed ≥ 24 weeks (i.e., GGI or GDM), or GDM by the one step procedure or a 1-hr 50-g glucose challenge test (GCT) ≥ 180 mg/dl performed ≥ 24 weeks

Identification of GGI 1-hr 50-g GCT (non-fasting), with plasma glucose at 1-hr ≥ 130 mg/dL

Identification of GDM by the two-step procedure

Identified as GGI, followed by a 3-hr 100g OGTT at ≥ 24 weeks after an overnight fast, with at least two of four plasma glucose values meeting or exceeding:

* Fasting: 95 mg/dL
* 1-hr: 180 mg/dL
* 2-hr: 155 mg/dL
* 3-hr: 140 mg/dl

Identification of GDM by the one-step procedure 75-g OGTT at ≥ 24 weeks after an overnight fast, with at least one plasma glucose value meeting or exceeding:

* Fasting: 92 mg/dL
* 1-hr: 180 mg/dL
* 2-hr: 153 mg/dL

Identification of GDM by 1-hr 50-g GCT

1-hr 50-g GLT (non-fasting), with plasma glucose at 1-hr ≥ 180 mg/dL at ≥ 24 weeks

Exclusion Criteria

* Indication that physical activity is or should be limited in the current pregnancy
* Previously diagnosed with diabetes (i.e., Type I or Type II diabetes) outside of pregnancy
* Current use of daily medications known to alter insulin resistance and/or metabolic profiles (e.g., metformin, corticosteroids, anti-psychotics)
* Current use of medication for polycystic ovarian syndrome (PCOS) (i.e., history of PCOS okay as long as she is not currently taking medication for PCOS)
* Condition or circumstance that would preclude their ability to follow a strict, time-based study protocol (e.g., psychiatric illness).