Diabetes in Pregnancy (Gestational Diabetes) — NZ Condition Guide | KiwiMeds

What is Diabetes in Pregnancy (Gestational Diabetes)?

Gestational diabetes mellitus (GDM) is diabetes that develops during pregnancy and usually goes away after birth. It occurs when the body cannot produce enough insulin to meet the increased demands of pregnancy, causing high blood sugar levels. GDM affects around 8–12% of pregnancies in New Zealand.

Overview

GDM usually has no symptoms and is detected through screening. Untreated GDM increases risks for both mother and baby: for the baby — larger birth size (macrosomia), low blood sugar after birth, breathing problems, and increased risk of type 2 diabetes later in life; for the mother — pre-eclampsia, caesarean delivery, and a 30–50% lifetime risk of developing type 2 diabetes. With good blood sugar management, most women have healthy pregnancies and babies.

Treatment in New Zealand

GDM is managed with blood sugar monitoring, dietary changes (reducing sugary and high-carbohydrate foods, consistent meal timing), and physical activity. If these measures are insufficient, insulin injections are used — they are safe in pregnancy and funded by Pharmac. Metformin is sometimes used as an alternative. After birth, blood sugar is checked again. Blood sugar usually returns to normal, but annual diabetes screening is recommended.

NZ-Specific Information

All pregnant women in NZ are offered screening for GDM with an oral glucose tolerance test (OGTT) between 24–28 weeks gestation (earlier if risk factors are present). Māori and Pacific women have higher rates of GDM. Midwives, GPs, and obstetricians provide coordinated care for GDM during pregnancy.

Frequently Asked Questions

Will I definitely get type 2 diabetes after GDM? Not definitely — but the risk is significantly elevated (around 50% lifetime risk). Annual diabetes screening, maintaining a healthy weight, and staying active are important for prevention. Is GDM my fault? No — GDM results from pregnancy hormones affecting insulin action. It is not caused by eating too much sugar during pregnancy.

Supplements That May Support Management

⚠️ Important: The supplements listed below have varying levels of clinical evidence. They are not a substitute for prescribed medications and should only be considered as adjunctive support under the guidance of a qualified healthcare professional. Always inform your GP or pharmacist before commencing any supplement, as interactions with prescribed medicines are possible.

• Vitamin D — Vitamin D deficiency is associated with increased gestational diabetes risk and worse glycaemic control. Supplementation (1000–2000 IU/day, as advised by your LMC or obstetrician) supports insulin sensitivity and foetal bone development.
• Magnesium — Magnesium improves insulin receptor sensitivity and is commonly deficient in pregnancy. Supplementation at 200–400 mg/day (as directed) may improve glycaemic control and reduce the risk of pregnancy complications.
• Inositol (Myo-Inositol) — Myo-inositol supplementation in pregnancy has demonstrated reductions in gestational diabetes incidence in women with polycystic ovary syndrome and those at high risk. It improves insulin sensitivity safely in pregnancy.
• Omega-3 Fatty Acids — DHA supplementation during pregnancy supports foetal neurological development and may modestly improve insulin sensitivity. DHA 200–400 mg/day is recommended in pregnancy regardless of gestational diabetes status.

Relevant Vaccinations

Individuals living with gestational diabetes may benefit from the following vaccinations. Please discuss your vaccination status with your GP or practice nurse, as eligibility and funding through the New Zealand National Immunisation Schedule may apply.

• Influenza (annual) — Pregnant women are at significantly increased risk of severe influenza complications. Influenza vaccination is safe in all trimesters and is funded in NZ for pregnant women. It also provides passive immunity to the newborn.
• Pertussis/Tdap (in each pregnancy) — A pertussis booster (in the Tdap combination) is recommended in each pregnancy (weeks 16–32) to protect the newborn against whooping cough. This is funded in NZ.
• COVID-19 — Pregnant women with gestational diabetes have elevated COVID-19 risk. COVID-19 vaccination is recommended in pregnancy — discuss timing with your LMC.

Dietary Guidance

Evidence-based dietary modifications play a meaningful role in the management of gestational diabetes. The following foods are generally recommended as part of a balanced, condition-appropriate diet. A referral to a registered dietitian may be beneficial for personalised nutritional planning.

• Low glycaemic index dietary pattern — The cornerstone of gestational diabetes dietary management. Low-GI foods reduce post-prandial glucose spikes and insulin requirements, reducing the risk of foetal macrosomia and birth complications.
• Consistent carbohydrate distribution (3 meals + 2–3 snacks) — Distributing carbohydrate evenly across the day reduces glycaemic variability. Skipping meals or eating large carbohydrate loads at once causes excessive glucose excursions.
• High-protein foods (lean meat, fish, eggs, legumes) — Protein slows carbohydrate absorption and supports stable blood glucose between meals while meeting increased pregnancy protein requirements.
• Non-starchy vegetables (unlimited) — Provide fibre, micronutrients, and minimal glycaemic impact. The most important dietary group in gestational diabetes management.
• Limit: fruit juice, dried fruit, white bread, white rice, sugary drinks — These are high-GI foods that rapidly elevate blood glucose. Whole fruit in moderate amounts (1–2 servings/day) is generally better tolerated than juice.

Related Conditions & Medications

Related medications: Insulin, Metformin. Related conditions: Type 2 Diabetes.