Joanne, maybe it will be help ? I just found a bit information about it
"In healthy pregnant women, the blood glucose level (serum sugar) is lower at around 60 - 80 mg%, (3.3 - 4.3 mmol / l), after a meal the increase is greater in pregnant women. In pregnant women there is an increased spontaneous and post-insulin secretion, and the transfer of glucose to the fetus depends on the amount of glucose in the mother's blood and on the needs of the placenta itself).
Deficiency of insulin produced by the pancreas results in hyperglycemia, glycosuria, ketonemia, emaciation, and dehydration. In pregnancy, additional factors appear that have anti-insulin effects: placental lactogen, estrogen and progesterone, prolactin, placental insulin, and so the amount of insulin decreases, and thus increases the level of glucose in the serum.
The first trimester improves the tolerance of carbohydrates and reduces the need for insulin (the fetus gets glucose and amino acids). In the second and third trimester, the carbohydrate metabolism deteriorates and, therefore, the insulin requirement increases by 50-70%. Before the birth, the need for insulin may be reduced, because the fetus produces its own insulin. After delivery, the need for insulin drops by 30 - 50%.
Glucose transport through the placenta is based on simplified diffusion, the higher the concentration of glucose in the mother's serum, the more it passes through the placenta to the fetus."