Maturity-onset diabetes of youth (MODY) are the most frequent monogenic diabetes with autosomic dominant inheritance (2% of diabetes). The MODY2 diabetes is related to a defect in the glucokinase (GCK) enzyme, the first limiting step of insulin secretion. An abnormal GCK leads to a delayed insulin secretion. Patients with GCK mutations have only mild raised fasting plasma glucose. Treatment is usually unnecessary since hyperglycemia is stable and MODY2 patients have no microvascular complications of diabetes. In contrast, pregnancy in MODY2 women is a challenging situation. A non-mutated fetus will produce excess insulin in response to raised maternal blood glucose leading to an accelerated growth and a higher risk of macrosomia. The mother of non-mutated fetus should therefore be treated to normalize her blood glucose levels. On contrary, a mutated fetus will produce a delayed insulin secretion (as his MODY2 mother) in response to maternal hyperglycemia. Consequently insulin therapy during pregnancy would reduce fetal insulin secretion and result in a low birth weight. Moreover, insulin therapy exposes pregnant women to more labor induction, prematurity and cesarean deliveries. In these MODY2 women whose glucose set point is physiologically higher, glycemic goals are difficult to achieve while often requiring extensive insulin therapy. An optimal situation would consist in initiating insulin therapy only for women with non-mutated offsprings. Unfortunately no antenatal diagnosis of the GCK mutation on fetal cells is available yet. In literature, birth weight differences between mutated and non-mutated neonates may reach up to 700g. In clinical practice, two strategies are used but without standardized protocol on glycemic targets, delay and doses of insulin : 1) insulin at diagnosis of pregnancy 2) treatment based on fetal abdominal circumference and fetal weight measurements by ultrasonography (US) and initiated if fetal biometry is greater than the 75th percentile. The purpose of the study is to evaluate for the first time these two management strategies through a prospective and standardized study. Hypothesis: US assessment would be sufficient to identify fetuses at risk of macrosomia and to initiate insulin treatment in mothers.
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Birth weight for gestational age
Timeframe: at birth