Causes Of Gestational Diabetes

Introduction

Gestational diabetes is a highly common occurrence during pregnancy which originates due to hormonal imbalances affecting the blood sugar regulatory system. Whilst the condition itself poses some risks and dangers to both the mother and baby, careful management and early detection provide the pair with optimal changes for typical healthy progression post pregnancy.

What is gestational diabetes?

Gestational diabetes refers to elevated blood glucose (sugar) levels that develop during pregnancy and typically self-correct post-pregnancy. The condition occurs when the body cannot produce enough insulin - the hormone that controls blood glucose - to meet the individual’s additional needs during pregnancy. Consequently, pregnant individuals often experience hyperglycaemia, meaning their blood sugar levels are elevated since excessive amounts of glucose remain within their bloodstream.

Typically, in non-diabetic individuals, after eating or drinking, the body alerts the pancreas to release insulin, which breaks down the glucose in our bloodstream so that it can be absorbed by the body’s cells or alternatively stored by the liver for later use. However, in individuals with gestational diabetes, this self-regulating cycle is disrupted since pregnancy hormones released by the pancreas contribute to insulin resistance. As a result, there is, firstly, not enough insulin to break down all the glucose in the blood, and secondly, the available insulin does not work as efficiently as it should since the body’s cells do not properly respond to it. In turn, blood sugar levels remain high and bring with it adverse repercussions affecting both the individual and the baby both during and post-pregnancy.

More broadly, gestational diabetes affects at least 4 to 5 in every 100 women during pregnancy. It can develop at any stage of the pregnancy but is most common during the second or third trimester, with diagnoses usually occurring at the 24^th to 28th-week mark. It also affects women who have not previously been affected by diabetes. Nevertheless, whilst any woman can develop the condition, there are a number of risk factors.

Gestational diabetes is a serious condition that should not be overlooked given the various implications and complications it carries for both the individual and their baby. On the one hand, the baby could be born too early, weigh too much, suffer from low blood glucose (hypoglycaemia), have breathing problems, and be more likely to become overweight and develop type 2 diabetes with age. On the other hand, the mother faces an increased chance of miscarriage or stillbirth,¹ they are more likely to have a caesarean section because of the baby’s larger size, and they are more prone to develop type 2 diabetes later in life. Finally, the mother may also develop preeclampsia, which refers to high blood pressure (hypertension) and excessive protein in the urine during the second half of pregnancy. Such a condition can cause serious and potentially life-threatening issues.² Overall, given such drastic complications, it is pivotal that individuals with gestational diabetes detect their condition early on and manage it as best they can to prevent any longer-lasting consequences.

Symptoms

Gestational diabetes does not usually have any direct, noticeable manifestations given that most symptoms commonly occur during pregnancy. Nevertheless, some associated signs and symptoms of gestational diabetes include:

• Excessive urination, especially at night
• Increased thirst
• Dry mouth and blurred eyesight
• Feeling unusually fatigued and lethargic
• Genital itching or thrush
• Losing weight without trying to

Because we cannot rely solely on the condition’s symptoms, pregnant individuals are typically screened using the Oral Glucose Tolerance Test (OGTT) during the 24^th to 28^th week of pregnancy. Following this screening, if an individual is diagnosed with gestational diabetes, then their healthcare team will assist them in understanding and managing the condition.

The placenta and gestational diabetes

Gestational diabetes occurs when hormones released by the placenta inhibit insulin.

The placenta is a structure within the uterus that provides a foetus (via. maternal blood) with the nutrients and oxygen it needs to survive and continue developing. Here, hormones which are chemical messengers play a pivotal role. More specifically, alongside the general hormones released by the pituitary gland in the brain, hormones produced by the placenta contribute towards the changes pregnant individuals experiences during and throughout gestation.³

There are numerous hormones produced by the placenta that help maintain the pregnancy. However, those specifically related to gestational diabetes include:

Human placental lactogen (hPL: otherwise known as the human chorionic somatomammotropin, HCS) which helps the baby grow and modifies the mother’s metabolism (i.e., how they change food and drink into energy for their body).⁴

Human placental growth hormone (hPGH) which helps regulate the mother’s blood glucose level to ensure the baby gets its necessary nutrients.⁴

These hormones are hyperactive during pregnancy and lead to increased insulin resistance alongside other physiological consequences.

Homeostasis and hormones

The introduction of extra hormones throws the usual homeostasis off balance. Homeostasis refers to any self-regulation process that helps maintain internal stability while adjusting to changing external conditions. This process is crucial for many of our behaviors and ultimately our survival, therefore anything that disrupts it results in grave repercussions.

Some of the placental hormones inhibit insulin

In terms of gestational diabetes, hormonal regulation is dysfunctional given that increased hormones released by the placenta circulate the bloodstream and disturb typical processes. Here, blood sugar regulation is directly affected.

More specifically, during pregnancy hPL is increased up to 30 times whilst hPGH increases up to 8 times, with both hormones causing maternal blood glucose levels to rise.⁵ Furthermore, the human placental lactogen is capable of altering insulin receptors, thereby diminishing glucose uptake and increasing insulin resistance.⁶ Meanwhile, the human placental growth hormone’s fat-mobilising properties (i.e., the release of fatty acids for use by the body when it needs energy) inhibit glucose disposal, thereby keeping glucose levels high and contributing to insulin resistance. Overall, it is evident that these extra pregnancy hormones throw the usual homeostasis off balance and often leave the mother suffering hyperglycaemia and pregnancy-induced insulin resistance.

Summary

Gestational diabetes refers to high blood sugar levels (hyperglycaemia) during pregnancy since the body cannot produce enough insulin to meet the individual’s additional needs during pregnancy. Whilst there are not many overt symptoms directly related to the condition, the oral glucose tolerance test administered later on in the pregnancy helps to catch the condition early on so it can be optimally managed.

The condition is primarily caused by the hormonal imbalance affecting the blood sugar regulatory system thanks to the increased hormones produced by the placenta during pregnancy, such as the human placental lactogen (hPL) and human placental growth hormone (hPGH). These hormones play a fundamental role in the regulation of foetal development;⁷ however, in doing so they contribute towards hyperglycaemia and insulin resistance.

Nevertheless, with attentive care and good management, this condition can be easily navigated and leave both the individual and their baby with minimal longer-lasting problems post-pregnancy.