by Subashni Thaver
QUESTION: My baby is four months old, but my blood glucose can rise above 17 mmol/L even though I take metformin 800 mg. Can I restart the insulin that was prescribed during pregnancy?
A glucose level above 17 mmol/L is above 306 mg/dL and needs prompt medical assessment. Do not restart leftover pregnancy insulin or change your metformin dose without current instructions. Insulin needs often change greatly after delivery, and the old insulin may have the wrong dose, type, storage condition, or expiration date. Contact your diabetes clinician today. Go to emergency care for vomiting, abdominal pain, rapid or difficult breathing, fruity-smelling breath, confusion, severe weakness, dehydration, fainting, inability to keep fluids down, or moderate or high ketones.
Answer by Dr. Albana Greca, MD, MMedSc
Congratulations on your baby. Persistent high glucose four months after delivery should not be assumed to be temporary gestational diabetes. It may represent ongoing type 2 diabetes, diabetes that was present before pregnancy, or less commonly another form such as autoimmune diabetes.
Insulin resistance falls rapidly after the placenta is delivered, so a dose used during pregnancy may be too high after birth and could cause severe hypoglycemia. At four months postpartum, the correct dose still depends on your current glucose pattern, meals, breastfeeding, weight, kidney function, and the insulin product.
Do not use insulin that is expired, was stored incorrectly, looks abnormal, or was prescribed under an old plan. If insulin is needed now, your clinician should confirm the product, dose, timing, glucose targets, and low-glucose plan. Our insulin treatment guide explains why doses must be individualized.
Seventeen mmol/L is approximately 306 mg/dL. Wash and dry your hands, repeat the test once with a fresh strip, and record whether it was fasting or after a meal. A result that remains around 300 mg/dL or higher needs same-day medical advice, especially with thirst, frequent urination, blurred vision, weakness, infection symptoms, or weight loss.
If ketone strips are available, check ketones when glucose is this high or when you feel unwell, but do not delay urgent care to obtain them. Review the warning signs on our page about dangerous blood sugar levels.
Women with gestational diabetes should have a 75-gram oral glucose tolerance test 4–12 weeks after delivery. Because your baby is now four months old and glucose remains high, arrange testing now if it was not completed. Your doctor may use fasting plasma glucose, HbA1c, and sometimes an oral glucose tolerance test to confirm the diagnosis and guide treatment.
Bring your pregnancy records, current meter, glucose log, metformin package, and old insulin details. Our guide to diabetes blood tests explains how fasting glucose and HbA1c are interpreted.
Metformin generally passes into breast milk in very small amounts, and available studies have not shown adverse effects in healthy breastfed infants. Routine glucose testing of a healthy baby is not usually required solely because the mother takes metformin. Extra caution may be needed for a premature newborn or an infant with kidney problems.
Insulin can also be used during breastfeeding, but the dose must be prescribed for your current needs. Breastfeeding can affect maternal glucose and may increase the risk of low glucose in people using insulin, so monitoring and a written treatment plan are important.
Use a blood sugar log to record the result, test time, meals, medicines, breastfeeding, symptoms, and any ketone reading.
Choose regular balanced meals with nonstarchy vegetables, protein, high-fiber carbohydrate, and healthy fats. Avoid sugary drinks and large portions of refined carbohydrates. Drink enough fluid unless you have a medical restriction.
Do not begin intense exercise while glucose remains around 300 mg/dL, particularly if you are unwell, dehydrated, or may have ketones. Postpartum weight may contribute to insulin resistance, but it should not be blamed as the sole cause, and breastfeeding does not guarantee weight loss.
Go to emergency care if glucose stays at or above 300 mg/dL with vomiting, abdominal pain, rapid breathing, fruity breath, confusion, severe drowsiness, dehydration, high ketones, or inability to keep fluids down. Do not take an unprescribed correction dose, double metformin, or use insulin left from pregnancy while waiting.
Please contact your doctor or diabetes clinic today. Persistent postpartum hyperglycemia requires a confirmed diagnosis and a current treatment plan. Insulin may be appropriate and is compatible with breastfeeding, but it must be restarted only with a newly prescribed dose and instructions. Do not stop metformin unless your clinician advises it.
Educational safety note: This answer is for general diabetes education only. It does not replace personal medical advice, diagnosis, or treatment. Do not start, stop, or change insulin, metformin, other medicines, supplements, diet, or exercise plans without speaking with your healthcare provider.
Last reviewed: July 2026.
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