Understanding gestational diabetes: causes and care

Gestational diabetes is a form of diabetes mellitus that appears for the first time in the 2nd or 3rd trimester of pregnancy [1]. Your body produces insulin, but the hormones secreted by the placenta partially block its action. When your pancreas cannot produce enough insulin to compensate for this increased resistance, your blood glucose rises above normal values [2].

The process develops gradually, as the placenta grows and releases ever larger amounts of diabetogenic hormones [1]. Factors such as being overweight before pregnancy, being over 25 years of age, and a family history of type 2 diabetes increase the risk of developing this condition. However, gestational diabetes can also occur in women without obvious risk factors.

Gestational diabetes differs fundamentally from the other types through its temporary cause, which is specific to pregnancy [2]. In type 1 diabetes, the immune system destroys the insulin-producing cells, and this destruction is permanent. In type 2 diabetes, the body becomes resistant to insulin over several years because of lifestyle and genetic predisposition.

In gestational diabetes, insulin resistance is caused by placental hormones and usually disappears after birth [1]. It is not an autoimmune disease, nor does it involve the destruction of the pancreatic beta cells. Treatment is generally needed only during pregnancy, although the risk of later developing type 2 diabetes remains increased [3].

Before pregnancy, your pancreas produced enough insulin for your body's needs. There were no placental hormones interfering with the action of insulin. Your body maintained a balance between insulin production and the glucose requirements of your cells [4].

Pregnancy creates an additional metabolic demand on the body. Placental hormones progressively increase insulin resistance, and the pancreas must double or even triple its insulin production [1]. If this adaptive capacity is exceeded, hyperglycemia appears, that is, gestational diabetes.

Gestational diabetes is by definition a temporary condition, which resolves in most cases after birth [2]. When the placenta is delivered, the hormones responsible for insulin resistance disappear rapidly [1]. Blood glucose usually returns to normal values within the first days after birth.

However, temporary does not mean without long-term consequences. Between 30% and 50% of women with a history of gestational diabetes will develop type 2 diabetes within the next 15-20 years, and the lifetime risk can reach up to 60% [3]. That is why blood glucose monitoring after birth and adopting a healthy lifestyle are essential for preventing type 2 diabetes.

Gestational diabetes most often appears in the second trimester, usually between weeks 24 and 28 of pregnancy [2]. This is the period when the placenta reaches a size large enough to produce significant amounts of diabetogenic hormones. That is precisely why the glucose tolerance test (OGTT) is carried out in this interval [3].

In the third trimester, insulin resistance continues to rise, at a slower pace, and reaches its peak in weeks 32-36 [1]. Some cases of gestational diabetes are diagnosed later, if the standard screening was negative but the risk factors persist and express themselves later on. A diagnosis of diabetes in the first trimester is in fact pre-existing diabetes that was not diagnosed before pregnancy.

Gestational diabetes affects between 10% and 14% of pregnancies worldwide, with variations depending on the population studied and the diagnostic criteria used [5]. Prevalence varies significantly between regions, being higher in the Middle East, North Africa, and Southeast Asia [2].

Over recent decades, the incidence of gestational diabetes has risen steadily, in parallel with the global obesity epidemic [2]. Lifestyle changes, more advanced maternal age, and the rising prevalence of obesity all contribute to this trend. The standardization of the IADPSG diagnostic criteria has allowed a more accurate global estimate of this condition [5].

Several hormones secreted by the placenta interfere with the action of insulin [4]. Human placental lactogen (hPL) is the main culprit, increasing insulin resistance by stimulating lipolysis and the release of free fatty acids into the circulation [1]. Progesterone and estrogen also contribute to reducing the tissues' sensitivity to insulin.

Cortisol, produced especially by the adrenal glands, also rises in pregnancy and amplifies insulin resistance by activating glucocorticoid receptors [6]. The placenta produces an enzyme that raises the local level of cortisol. Placental growth hormone and leptin round out this complex hormonal picture, which puts pressure on the pancreas's capacity to secrete insulin [4].

Yes, gestational diabetes can theoretically occur in any pregnancy, including in women without apparent risk factors. However, the risk is significantly higher if you had gestational diabetes in a previous pregnancy [7]. Between 30% and 50% of affected women will develop this condition again in subsequent pregnancies, with higher rates in high-risk populations [8].

Other factors that increase the likelihood include being overweight, being over 35 years of age, a family history of type 2 diabetes, and polycystic ovary syndrome [3]. The fact that you had a pregnancy without gestational diabetes does not guarantee that the next pregnancies will be the same. Each pregnancy must be monitored individually, and blood glucose testing remains mandatory.

The placenta influences glucose metabolism in order to ensure a continuous supply of nutrients to the fetus [6]. The fetus depends exclusively on maternal glucose for its growth and development, as it cannot produce what it needs on its own. By increasing the mother's insulin resistance, the placenta directs more glucose toward the fetal circulation [4].

This mechanism is an evolutionary adaptation that works perfectly when the maternal pancreas is able to compensate [6]. The placenta acts as a complex endocrine organ, secreting hormones that reconfigure the mother's metabolism. When this reconfiguration exceeds the mother's adaptive capacity, the result is gestational diabetes [1].

After the placenta is delivered, the hormones responsible for insulin resistance disappear rapidly from the circulation [1]. In most cases blood glucose returns to normal within the first hours or days after birth. Treatment with insulin or oral antidiabetic medication is usually stopped immediately after birth, with monitoring of blood glucose [2].

However, it is essential to undergo a glucose tolerance test 6-12 weeks after birth, to confirm that the problem has resolved [3]. The risk of developing type 2 diabetes remains increased over the long term, which is why a long-term annual check-up is recommended. Breastfeeding, maintaining a normal weight, and regular physical activity can significantly reduce the risk of developing type 2 diabetes in a mother with a history of gestational diabetes [9].