Gestational diabetes (GD) is a condition where high blood sugar levels develop during pregnancy in individuals who did not have diabetes beforehand. This metabolic change can emerge as pregnancy progresses, typically around the 24th to 28th week. While the precise reasons for GD are not fully understood, the placenta, an organ that supports the developing fetus, plays an important role in its onset and progression.
The Placenta’s Hormonal Influence
The placenta is an organ that forms in the uterus during pregnancy, serving as a temporary interface between the mother and the developing fetus. It produces various hormones essential for pregnancy and fetal growth, including human placental lactogen (HPL), progesterone, estrogen, cortisol, and placental growth hormone.
These placental hormones naturally increase a mother’s insulin resistance, a process often referred to as the “contra-insulin effect.” This physiological change ensures that more glucose remains in the mother’s bloodstream, readily available for transport across the placenta to meet the energy demands of the growing fetus. As the placenta grows larger, it produces more of these hormones, which can further intensify insulin resistance.
Often, the mother’s pancreas can compensate for this increased insulin resistance by producing additional insulin to maintain normal blood sugar levels. However, in some individuals, the pancreas cannot produce enough insulin to overcome this resistance. When this compensation fails, blood glucose levels become elevated, leading to the diagnosis of gestational diabetes.
Impact of Gestational Diabetes on Placental Function
While the placenta’s hormones contribute to the development of gestational diabetes, the presence of uncontrolled GD can, in turn, affect the placenta itself. The altered metabolic environment of gestational diabetes can lead to structural and functional changes within the placenta. These changes can include increased placental size and thickness, as well as alterations in its vascularization.
Changes are observed in the placenta’s villous structure, including villous immaturity and various vascular lesions, in pregnancies affected by GD. The increased glucose in the maternal blood can also cross into the placenta, influencing its health and efficiency. This can lead to impaired nutrient transport and reduced oxygen transfer to the fetus.
Gestational diabetes can contribute to low-grade inflammation and oxidative stress within the placenta. This inflammatory environment, along with hormonal imbalances, can further affect the placenta’s size and vascularity, potentially leading to dysregulation in both maternal and fetal blood circulations. These internal changes within the placenta can exacerbate existing issues and contribute to complications for both the mother and the baby.
Placenta-Related Complications for Mother and Baby
The placenta’s involvement in gestational diabetes can lead to various complications for both the mother and the developing baby. For the baby, one common outcome is macrosomia, defined as a birth weight of 4,000 grams (approximately 8 pounds, 13 ounces) or more. This occurs because excessive glucose from the mother’s blood crosses the placenta, causing the fetal pancreas to produce more insulin, which converts the extra glucose into fat, leading to excessive growth.
After birth, babies of mothers with gestational diabetes may experience neonatal hypoglycemia, or low blood sugar. This happens because the baby’s pancreas, accustomed to high glucose levels in the womb, continues to produce a high amount of insulin even after the maternal glucose supply is cut off, causing a rapid drop in their blood sugar. Other potential complications for the baby include jaundice, respiratory distress syndrome, and an increased long-term risk of developing obesity and type 2 diabetes.
For the mother, gestational diabetes increases the risk of preeclampsia, a condition characterized by high blood pressure and organ damage. The presence of macrosomia can also increase the likelihood of needing a Cesarean section due to the baby’s large size, which can make vaginal delivery challenging. Women who experience gestational diabetes have a higher future risk, approximately 50%, of developing type 2 diabetes.