Insulin Clinics / Special situations

Sick days, exercise, and pregnancy

Three situations where the usual rules change. Each deserves a written plan from your care team — what follows is the principle behind those plans.

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If this is an emergency — severe low blood sugar, vomiting with high blood sugar, confusion, or trouble breathing — call your local emergency number now. This site is reference information, not medical advice.

Sick days

Why illness raises blood sugar

When the body is fighting an infection, the immune system releases stress hormones — cortisol, adrenaline, glucagon, growth hormone — that all raise blood glucose. Insulin resistance increases. Many people see glucose rise even when they are eating less than usual, sometimes dramatically. Common cold, flu, gastroenteritis, urinary tract infections, dental infections, and COVID can all do this.

Do not stop basal insulin

The most important sick day rule, especially in type 1 diabetes: do not stop your basal insulin. Basal covers the liver's glucose release, which continues regardless of whether you are eating. Stopping basal because "I'm not eating much" is one of the fastest paths to DKA. The dose may need to come down a little — your care team will guide that — but it almost never goes to zero.

For people on basal-bolus regimens, the typical pattern during illness is: keep basal at home dose (sometimes increase by 10–20 percent), reduce or skip mealtime insulin if you cannot eat, and add correction doses based on glucose checks every 2–4 hours.

Hydration

High glucose pulls water out of you through frequent urination, and illness already strains hydration. Drink steadily throughout the day:

If glucose is high (over 180–250): sugar-free fluids — water, broth, sugar-free electrolyte drinks, herbal tea.
If glucose is low or normal and you cannot eat solid food: small amounts of regular soda, juice, popsicles, ice cream, broth — anything you can keep down.
Aim for small sips frequently rather than large amounts at once if you are nauseated.

Ketone monitoring

Test for ketones any time blood glucose is over 250 mg/dL during illness, any time you are vomiting, and at least once a day if you are sick enough to consider missing work or school. The page on high blood sugar and DKA covers what the results mean.

People taking SGLT2 inhibitors (empagliflozin, dapagliflozin, others) have a higher risk of DKA at lower glucose values during illness. Many specialists ask people on these medications to hold them while sick — but only with the prescriber's instruction.

When to call the care team

Blood glucose stays above 250 for more than a few hours despite corrections.
Any moderate or large urine ketones, or blood ketones above 1.5 mmol/L.
Cannot keep any fluid down for 4 hours.
Vomiting more than twice, or any vomiting in young children with diabetes.
Fever above 101°F (38.3°C) for more than 24 hours.
Diarrhea more than 5 times a day, or any blood in stool.
You are unsure how to adjust insulin and your written plan does not cover the situation.

Exercise

Activity is one of the most powerful tools in diabetes care — and one of the most likely causes of low blood sugar in someone using insulin. The interaction depends on the type of activity, the timing relative to insulin, and what you have eaten.

How different intensities affect glucose

Steady aerobic exercise (walking, jogging, cycling at conversational pace): muscles take up glucose using less insulin than usual; glucose typically falls during and after.
High-intensity interval exercise or resistance training: stress hormones can briefly push glucose up during the workout, then it falls afterward — sometimes hours later.
Mixed activity (most team sports): both effects play out, often with a net drop afterward.
Strength training alone: less glucose-lowering per session than aerobic work, but it improves insulin sensitivity over weeks.

Pre-exercise checks

Many clinicians recommend the following framework before a planned workout:

Glucose under 90 mg/dL: eat 15–30 grams of carbs without insulin before starting; recheck in 15 minutes.
90–180 mg/dL: for moderate exercise, you can usually start; consider a small snack if the session is long.
180–250 mg/dL: generally safe to exercise; for type 1 diabetes, check ketones if glucose has been high for hours.
Above 250 mg/dL with ketones: postpone exercise. Activity in this state can worsen ketosis.

Trend matters as much as the number. Glucose dropping fast before a workout is a different situation from steady glucose at the same value, and CGM trend arrows are very useful here.

Carb adjustments

Common general approaches (always individualized with your care team):

For exercise within 1–2 hours after a meal, reduce the meal bolus by 25–75 percent depending on intensity and duration.
For exercise more than 2 hours after the last bolus, eat 15–30 grams of carbs per 30–60 minutes of activity, more for higher intensity.
Long endurance activity (over an hour) typically requires both reduced insulin and ongoing carbs.

Post-exercise lows — including delayed lows

The risk of low blood sugar after exercise extends well beyond the workout. Muscles continue to take up glucose to refill their stores for several hours, and overnight lows after evening exercise are well-documented. Practical points:

Check glucose right after a workout, an hour later, and before bed.
Many people need a smaller dinner bolus or a slightly reduced overnight basal after a heavy workout day.
A bedtime snack with carbs and protein can help blunt overnight lows.
Closed-loop pump systems generally reduce overnight basal automatically when sensor glucose drops, which has reduced post-exercise lows substantially in studies.

Patterns matter. If you exercise three times a week, look at glucose patterns on workout days vs rest days for two weeks — the differences are usually clear and the adjustments emerge from there.

Pregnancy

Pregnancy with diabetes — pre-existing or newly diagnosed — requires close, specialist care. This page is overview only. The right plan for you will come from a maternal-fetal medicine team or endocrinologist working with your obstetric provider.

Why insulin needs change in pregnancy

Hormones from the placenta cause insulin resistance that increases progressively, especially after the first trimester. Insulin requirements often climb steadily through the second and third trimesters and can double or more by the third trimester compared with pre-pregnancy. Just before delivery, requirements often plateau or even fall slightly. After delivery, they typically drop sharply — sometimes within hours — and the dose returns to pre-pregnancy levels or lower for those who are breastfeeding.

For people with type 1 diabetes, the first weeks of pregnancy can also bring more frequent lows as insulin sensitivity briefly increases.

Why pregnancy planning matters

Many of the most serious risks of diabetes in pregnancy — to the developing baby and to the parent — are highest in the first 8–10 weeks, often before someone knows they are pregnant. The single biggest thing that lowers risk is starting pregnancy with A1C close to target. Pre-conception care typically includes:

Tightening A1C, ideally below 6.5 percent, before conception when it can be done safely.
Reviewing all medications — some diabetes medications (and many others, including ACE inhibitors, statins, and certain blood pressure drugs) need to be changed before pregnancy.
Eye and kidney evaluation, since both can change rapidly in pregnancy.
High-dose folic acid (often 1 mg or more, vs the 0.4 mg in standard prenatal vitamins) for at least 1–3 months before conception.
A specialist discussion about CGM and pump options — pregnancy targets are tighter than usual, and a CGM is now standard of care for type 1 diabetes in pregnancy.

Gestational diabetes

Gestational diabetes is high blood sugar that begins during pregnancy in someone who did not have diabetes before. Most people are screened with a glucose tolerance test between 24 and 28 weeks. Many people are managed initially with diet and activity changes; a substantial fraction need insulin (and sometimes metformin) as well. Insulin is the standard medication when one is needed because it does not cross the placenta in significant amounts.

Which insulins are commonly used in pregnancy

The strongest pregnancy safety data, accumulated over decades, are for:

Regular human insulin and NPH — the longest track record.
Insulin lispro and insulin aspart — extensively used and considered safe; often preferred over regular insulin for mealtime dosing because of better post-meal glucose control.
Insulin detemir — has good pregnancy data and is commonly used as basal.

For other insulins (glargine, degludec, glulisine, faster aspart, lispro-aabc), data are more limited but accumulating; many are used in pregnancy when continuing them is the better choice. The decision is individualized.

Pregnancy-specific glucose targets

Targets are tighter than for non-pregnant adults, because higher glucose increases risks of large birth weight, hypoglycemia in the newborn, and preeclampsia:

Fasting: typically below 95 mg/dL.
1-hour after meals: typically below 140 mg/dL, or 2-hour after meals below 120 mg/dL.
A1C: typically below 6.0–6.5 percent.
Time in range (63–140 mg/dL on CGM): 70 percent or more in type 1 diabetes during pregnancy.

Hitting these targets without lows is hard work and is exactly why pregnancy demands close specialist care.

After delivery

Insulin needs drop quickly after the placenta is delivered. Doses are usually reduced significantly within hours, and the team will often start with a much lower basal than the third-trimester dose. Breastfeeding lowers glucose further, and overnight lows during nursing are common.

For people who had gestational diabetes, there is an elevated long-term risk of type 2 diabetes; standard of care is a glucose tolerance test 4–12 weeks postpartum and screening every 1–3 years thereafter.