Gestational diabetes
One of the prenatal risk factors for ASD is gestational diabetes. During late pregnancy mothers can develop insulin resistance [201]. Gestational diabetes occurs in 2 to 3% of all pregnant women [202], although more current estimations indicate up to 14% of all pregnancies are affected by gestational diabetes depending on the test criteria used [203]. Elevated cortisol levels have been measured in pregnant women with impaired glucose tolerance or gestational diabetes [204]. Gestational diabetes is a growing health concern for both the short- and long-term outcomes for both mothers and their offspring [205]. Glucose tolerance deteriorates in all women where a diminished peripheral sensitivity to insulin develops [206]. Normal pregnancy especially the third trimester is characterised by elevated metabolic stress on maternal lipids and glucose homeostasis, which includes insulin resistance and hyperinsulinemia [207,208]. Progesterone receptors expressed in pancreatic islet cells inhibit β-cell proliferation to reduce insulin secretion and glucose tolerance during pregnancy [209]. Known risk factors for gestational diabetes include excessive weight, advanced maternal age, family history of Type 2 diabetes and a previous history of gestational diabetes [210-213]. Women with gestational diabetes have a high risk of developing Type 2 diabetes later in life [214,215]. Fetal hyperglycaemia as an outcome of maternal hyperglycaemia can contribute to excessive fetal growth [202]. However, gestational diabetes has paradoxical effects of fetal growth with outcomes of increased or decreased birth weight [216]. About 85% of term newborn infants are born with birth weights in the normal range of 2500 to 4000 g. Among full-term infants, 7 to 8% of newborns have a birth weight of <2500 g (10 percentile) and a similar percentage are born overweight (>4000 g, 90 percentile) [216].