Diagnosis of MODY during Pregnancy
The diagnosis and management of Maturity-Onset Diabetes of the Young (MODY) in pregnancy has some specific considerations including genetic, clinical, and management aspects. Of utmost importance are maternal, fetal, and neonatal outcomes.
Overview
Maturity-Onset Diabetes of the Young (MODY) is a monogenic form of diabetes, often misdiagnosed as type 1 or type 2 diabetes. It affects around 1–5% of people with diabetes but is commonly missed in primary care and antenatal settings.
For hapū māmā (pregnant mothers), recognising MODY is essential to ensure care is safe, personalised, and whānau-centred. Diagnosis and management must not only address blood glucose but also honour wairua (spiritual health), hinengaro (mental/emotional health), tinana (physical health), and whānau (family and social support).
Key features:
- Autosomal dominant inheritance → 50% chance of passing the mutation to the fetus.
- Diagnosing MODY during pregnancy is crucial to tailor management and avoid unnecessary insulin use or missed treatment.
Common MODY Subtypes in Pregnancy
| Subtype | Gene | Clinical Features | Pregnancy Considerations |
| MODY 2 (GCK) | GCK (glucokinase) | Mild, stable fasting hyperglycaemia (5.5–8 mmol/L); rarely develops complications | Usually no treatment needed unless rapid fetal overgrowth seen; fetal genotype determines risk |
| MODY 3 (HNF1A) | HNF1A | Progressive beta-cell dysfunction; sensitive to sulfonylureas | Treat with insulin or sulfonylureas; fetus risk of macrosomia if inherits variant |
| MODY 1 (HNF4A) | HNF4A | Similar to MODY 3; risk of neonatal hypoglycaemia and macrosomia | Requires close glucose management; neonatal glucose monitoring |
| Other subtypes | e.g., PDX1, KCNJ11, ABCC8 | Rare; variable presentation | Management individualized |
Health Care
A number of different hospital specialist teams will likely be involved the health care:
- Endocrinologist – MODY-specific management
- Diabetes Specialist Nurse and/or Dietitian – Support on diabetes management and monitoring
- Obstetric team – High-risk pregnancy monitoring
- Genetic counselor – Inheritance and testing discussions
- Neonatal team – Preparedness for hypoglycaemia management
Specifically with a New Zealand context, this care should embrace the following principles. We deserve it!
- Equity in access: Timely genetic testing should be available for Māori and Pacific women, who often face systemic barriers.
- Culturally safe care: Education and any decision-making should involve whānau/family where possible and as appropriate.
- Language and trust: Person-centred, strengths-based language should always be used to support understanding and engagement.
Diagnosis
Clinical clues
- Early-onset diabetes (<25 years) in mother or family members
- Strong family history, often across generations ( (vertical transmission)
- Lean or normal BMI, minimal insulin resistance
- Negative autoantibodies (GAD, IA2, ZnT8)
- Preserved C-peptide
Genetic testing
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Genetic testing is recommended if MODY is suspected, and should be offered in a mana-enhancing way, with clear explanations about what the test means for both māmā and whānau.
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Culturally safe information and support should be provided, recognising that genetic information may carry whakapapa (genealogy) significance.
- Testing helps guide maternal treatment and predict fetal outcomes.
Fetal assessment
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Ultrasounds are important, in order to monitor fetal growth and identify macrosomia or growth restriction.
Diabetes Management
Management approach will depend on the MODY subtype, and whether the fetus inherits the genetic mutation.
MODY 2 (GCK)
- Mild fasting hyperglycaemia typically does not require treatment, so Most hapū māmā do not need medication.
- Fetal growth monitoring:
- If pēpi inherits mutation → growth is normal; no intervention needed.
- If pēpi does not inherit mutation → increased risk of macrosomia → insulin may need to be started if fetal abdominal circumference >75th percentile.
MODY 3 (HNF1A) and MODY 1 (HNF4A)
- Before pregnancy: Oral sulfonylureas may be effective.
- During pregnancy:
- Insulin is often preferred because sulfonylureas cross the placenta and can cause neonatal hypoglycaemia.
- Close glucose monitoring and early adjustment of therapy.
- Pregnancy and medication changes can create stress or uncertainty, so early referral to a diabetes educator or counsellor is valuable.
- Fetal risk:
- 50% chance of inheriting the mutation → macrosomia and neonatal hypoglycaemia.
- Delivery planning: May require early induction if macrosomia or poor glycaemic control.
Postpartum
- Maternal: Adjust treatment postpartum (e.g., restart sulfonylureas for HNF1A or HNF4A MODY).
- Neonatal: Monitor blood glucose closely, especially for HNF4A MODY due to hypoglycaemia risk.
- Genetic counseling for family members. Whānau support should include ongoing education and ensure connection with community and Māori health providers for longer-term tautoko.
Monitoring
Maternal, Fetal and Neonatal monitoring are all important to ensure the best outcomes for māmā and pēpi.
There is a risk of baby growing too big too quickly. Due to higher than ideal maternal blood glucose levels, baby will make more insulin for itself and put on more weight.
There is a risk of baby having a low blood glucose level at birth due to higher than ideal maternal blood glucose levels during the pregnancy. This is because baby has been making more insulin than ideal and when disconnected at birth from māmā’s high blood glucose levels baby’s blood glucose levels can plummet.
| Subtype | Fetal Monitoring | Neonatal Care |
| GCK MODY | Serial ultrasounds; check for growth acceleration | Usually no intervention needed |
| HNF1A/HNF4A MODY | Growth scans every 2–4 weeks; watch for macrosomia | Early and frequent blood glucose monitoring |
Example Clinical Scenarios
Example Case 1 – GCK MODY
- Mild fasting hyperglycaemia, no treatment needed if fetus carries mutation.
- Insulin only if fetal growth suggests unaffected fetus with overgrowth.
Example Case 2 – HNF1A MODY
- Preconception sulfonylurea switched to insulin early in pregnancy.
- Weekly glucose profiles, fetal growth scans from 28 weeks.
Clinical Summary
| MODY Type | Maternal Treatment | Fetal Risk | Delivery & Postpartum |
| GCK (MODY2) | Usually no treatment; insulin if overgrowth in unaffected fetus | Macrosomia if fetus is unaffected | Normal care; no neonatal issues |
| HNF1A (MODY3) | Insulin during pregnancy | Macrosomia, neonatal hypoglycaemia | Resume sulfonylureas; monitor neonate |
| HNF4A (MODY1) | Insulin; careful glucose control | High risk of neonatal hypoglycaemia | Neonatal glucose monitoring required |
