Researchers wanted to understand how daytime exercise affects nighttime blood sugar levels in pregnant people with high blood sugar. They had 13 pregnant women wear a continuous glucose monitor (a small device that tracks blood sugar all day and night) and an activity tracker watch for one week. They found that doing more moderate-to-vigorous exercise during the day was linked to slightly higher blood sugar levels at night. This early study shows it’s possible to combine these two types of tracking devices, which could help doctors give pregnant women more personalized advice about exercise and blood sugar management.

The Quick Take

  • What they studied: Whether the amount of exercise pregnant women do during the day affects their blood sugar levels at night
  • Who participated: 13 pregnant women (around 31 weeks pregnant) who had high blood sugar during pregnancy, tracked using two wearable devices for 7 days
  • Key finding: Each extra 10 minutes of moderate-to-vigorous exercise during the day was linked to blood sugar that was about 0.86 mg/dL higher at night—a very small increase that may not be clinically meaningful
  • What it means for you: This is early research with a very small group, so we can’t make strong recommendations yet. It suggests that the relationship between daytime exercise and nighttime blood sugar is more complex than previously thought, and more research is needed before changing exercise advice for pregnant women with high blood sugar

The Research Details

This was a secondary analysis, meaning researchers looked at data that was already collected from a smaller feasibility study. Thirteen pregnant women (around 31 weeks along) wore two devices for one week: a continuous glucose monitor (CGM) that measures blood sugar every few minutes, and an activity tracker watch that records movement and sitting time throughout the day. The researchers then used statistical methods to look for connections between how much the women moved during the day and their blood sugar levels at night (between midnight and 6 AM).

The study measured three types of daytime activity: moderate-to-vigorous exercise (like brisk walking or jogging), light activity (like gentle movement), and sedentary time (sitting or lying down). For nighttime blood sugar, they looked at average glucose levels, how much time blood sugar stayed in a healthy range, and overall glucose exposure.

The researchers used advanced statistical models that account for the fact that they were measuring the same people multiple times over multiple days, which helps make the results more reliable.

Understanding how exercise affects blood sugar in pregnant women with high blood sugar is important because high blood sugar during pregnancy can lead to larger babies and increase the risk of health problems for both mother and baby. However, most previous research focused on how exercise affects blood sugar during the day, not at night. This study is one of the first to combine continuous glucose monitoring with activity tracking in this group, which could help doctors give better, more personalized advice.

This study is very small (only 13 participants), which is a major limitation. Small studies can show interesting patterns but aren’t strong enough to make definitive conclusions. The study was also short (only 7 days), so we don’t know if the patterns would continue over longer periods. The researchers did use objective measurement tools (devices that automatically record data rather than relying on people to remember), which is a strength. This was a feasibility study, meaning it was designed to test whether combining these two types of devices was even possible, not to prove that exercise changes nighttime blood sugar.

What the Results Show

The main finding was that doing more moderate-to-vigorous exercise during the day was linked to slightly higher blood sugar at night. Specifically, for every extra 10 minutes of moderate-to-vigorous exercise, nighttime blood sugar was about 0.86 mg/dL higher on average. This is a very small difference—for context, normal blood sugar ranges are typically 60-100 mg/dL, so this change is less than 1% of the normal range.

The study also looked at the total amount of glucose exposure at night (measured as area under the curve, or AUC). They found that each 10 minutes of moderate-to-vigorous exercise was linked to about 313 mg/dL*minutes higher AUC at night, which is a technical measure of overall glucose levels.

Interestingly, light activity (like gentle movement) and total sedentary time (sitting or lying down) were not linked to nighttime blood sugar levels. This suggests that only more intense exercise showed a connection, though the connection was small.

These results were surprising to the researchers because they expected that more daytime exercise would lead to lower nighttime blood sugar, based on what we know about how exercise affects blood sugar in general. Instead, they found the opposite pattern, though the effect was very small.

The study also examined whether the amount of time blood sugar stayed in a healthy range at night (60-99 mg/dL) was affected by daytime exercise, but they didn’t find a clear connection. This suggests that while daytime exercise may slightly raise average nighttime blood sugar, it doesn’t necessarily push blood sugar out of the healthy range. The researchers noted that combining these two types of tracking devices worked well and provided detailed information about both activity and blood sugar patterns.

Previous research has shown that exercise generally helps lower blood sugar in people with diabetes and high blood sugar. However, most of that research looked at blood sugar during and immediately after exercise, not at nighttime blood sugar many hours later. This study adds new information by looking at the delayed effects of daytime exercise on nighttime blood sugar. The unexpected finding (that more exercise was linked to slightly higher nighttime blood sugar) suggests that the relationship between exercise and blood sugar in pregnant women may be different from what we see in other groups, and that nighttime blood sugar may be influenced by factors other than just daytime activity.

This study has several important limitations. First, it’s very small—only 13 women—so the results might not apply to other pregnant women with high blood sugar. Second, it only lasted 7 days, so we don’t know if these patterns continue over weeks or months. Third, the study didn’t measure diet, which is a major factor affecting blood sugar, so we can’t tell if food choices were influencing the results. Fourth, the small sample size means the results could be due to chance rather than a real effect. Finally, this was a secondary analysis of data collected for a different purpose, so it wasn’t specifically designed to answer this question.

The Bottom Line

Based on this very early research, we cannot make strong recommendations about changing exercise habits during pregnancy with high blood sugar. Pregnant women should continue to follow their doctor’s advice about exercise. This study suggests that the relationship between daytime exercise and nighttime blood sugar is more complicated than previously thought, and more research with larger groups of women and longer study periods is needed before we can give personalized exercise recommendations based on nighttime blood sugar patterns. (Confidence level: Low—this is preliminary research)

This research is most relevant to pregnant women with gestational diabetes or gestational glucose intolerance, their doctors, and researchers studying pregnancy and blood sugar. It’s not yet ready to change clinical practice. People without pregnancy-related high blood sugar don’t need to change their behavior based on this study.

Because this is very early research, we don’t yet know what realistic timelines for benefits would be. Future studies will need to track women over weeks and months to understand how exercise patterns affect blood sugar over time during pregnancy.

Want to Apply This Research?

  • If you have gestational diabetes or high blood sugar in pregnancy and your doctor approves, track daily moderate-to-vigorous exercise minutes (like brisk walking, swimming, or cycling) and correlate it with your continuous glucose monitor readings the following morning to see if you notice personal patterns
  • Work with your healthcare provider to establish a personalized exercise routine, then use the app to log exercise type and duration alongside glucose readings to identify your individual response patterns—what works for one person may differ for another
  • Keep a 2-week log of daily exercise minutes and nighttime average glucose levels to establish your personal baseline, then share this data with your doctor to help guide individualized recommendations rather than relying on general guidelines

This research is preliminary and based on a very small study (13 participants) lasting only 7 days. It should not be used to change exercise recommendations during pregnancy. Pregnant women with high blood sugar should follow their healthcare provider’s personalized advice about exercise, diet, and glucose management. This study does not establish that daytime exercise causes changes in nighttime blood sugar—only that a small association was observed. Anyone pregnant with high blood sugar should consult with their obstetrician or maternal-fetal medicine specialist before making any changes to their exercise routine or diabetes management plan.