Pregnancy and the Invisible Transformation

What comes to your mind when you think about pregnancy?

Growing belly, Morning sickness. Cravings. Swollen ankles. Pin ultrasound pictures to the refrigerator. Outwardly, these are the signs that a person is transforming. Under the surface of maternity jeans and mirrors, the most profound changes are occurring invisibly and quietly.

The pregnancy doesn’t only grow a child. It reprograms the body of a woman in many ways. What are two of the most fascinating and overlooked areas of change? Her metabolic and immune system.

Take a look at how a woman’s uterus adapts to carry a new baby. Understanding these changes could one day be used to treat diseases such as diabetes, autoimmune disorders, and cancer.

What is metabolism, and why does it matter during pregnancy?: Pregnancy and the Invisible Transformation

Let’s first define metabolism. The process by which your body transforms the food that you eat into energy is called metabolism. Your body uses carbohydrates, fats and proteins as fuel to do everything from think and breathe to grow new life.

The energy requirements of your body increase dramatically when you are pregnant. You’re not only keeping your cells alive, but you’re also building a new human. Your metabolic system will have to work overtime.

It doesn’t just do it randomly. Your body has a highly coordinated plan to adjust your metabolic rate across the various stages of pregnancy.

Early Pregnancy: Store Now, Spend Later

During your first and second trimesters of pregnancy, your body adopts a “save-and-store” approach. Estrogen (one of the key hormones during pregnancy) and progesterone increase appetite and promote fat storage. This could explain why so many women are ravenous in the early stages of pregnancy. Your body is preparing a reserve of energy for later.

This is like building up a biological bank account. By storing fat early, you can have a reserve of energy when you reach the third trimester.

Late Pregnancy: Baby Burn

Your metabolism will shift again by the third trimester. It’s now time to use those resources. Your body becomes better at converting fat into fuel. It also develops Insulin Resistance, which on the surface sounds bad, but is a clever adaptation.

Insulin is a hormone that helps to move glucose (sugar) from your bloodstream into your cells. When your body becomes less sensitive, glucose levels in the blood increase. This glucose is then sent to your baby and placenta for growth.

Gestational diabetes is caused by this natural insulin resistance that occurs during pregnancy. They can’t keep up with metabolic demands, and their blood sugar levels rise. This is why screening for gestational diabetes during the second pregnancy is standard.

Even without a diagnosis of diabetes, the change in metabolism is dramatic during pregnancy. Many women burn fat in a way they have never done before by the third trimester. They are essentially in a temporary and safe version of ketosis.

Immunity and Pregnancy – A Balanced Act

While your body is busy adjusting to the new baby, your immune system has been working just as hard: it is finding a way for your body to tolerate this child without compromising its defences.

Consider this: Your baby is half of you and half of your partner. In terms of immunity, this means that the fetus has “foreign DNA”. Your immune system would recognise foreign cells in any other situation and attack them. This would be the same as a virus or an organ transplant.

Not during pregnancy. The immune system performs an amazing feat, protecting both mother and child while preventing an attack by the immune system on the fetus. It does not do this by turning off, but by recalibrating.

What exactly changes in the Immune System occur?

Here is a closer look at some of the major immune system changes that occur during pregnancy.

• The monocytes (a white blood cell type) are more active and take on a greater role in defence.
• Neutrophils are another type of white cell that increases in number. They are the first cells to respond when there is an infection or injury.
• T-cells change their behaviour. They are responsible for the long-term memory of immune responses. They begin releasing proteins and mediators, which are chemical signals that guide immune responses.

Some of these changes prevent your immune system from rejecting the child. Other methods are used within the uterus where immune cells such as natural killer cells (NK), and specialised T-cells accumulate. These cells play a part in helping to develop the placenta.

These immune cells produce signalling molecules, including proteins, cytokines and hormones, that regulate the nutrient exchange between mother and baby to ensure proper growth and development.

While we normally think of immune cells in pregnancy as fighters, they also become builders and communicators.

But there’s a trade-off…

All of these changes in immunity come with a price.

Pregnant women are more susceptible to infections due to the recalibration of their immune system. This is especially true for viruses such as influenza. Although we don’t know why or which immune pathways have been altered, the result is that pregnancy can increase the likelihood of a more serious illness caused by flu or other infections.

It’s for this reason that flu vaccinations are recommended in pregnancy. Not only to protect the mother but also to protect the baby.

Pregnancy, Autoimmune Diseases

The immune changes during pregnancy can also have an impact on women who suffer from autoimmune disease, where the immune system attacks the body’s cells.

As an example:

• Women who have MS or Rheumatoid Arthritis (RA) may feel better during pregnancy. They can temporarily or permanently reduce their symptoms.
• Women with Systemic Lupus Erythematosus may experience worsening of symptoms while pregnant.

As soon as pregnancy hormones are no longer present, the autoimmune symptoms can return to their pre-pregnancy state, sometimes in just a few days.

Scientists believe the changes in behaviour of T cells and immune mediators that occur during pregnancy are key factors. We might be able to develop a new treatment for autoimmune disease if we better understand these mechanisms.

Why does this matter beyond pregnancy?

You might think: This is interesting, but how practical is it?

Scientists are learning how to use these systems in other conditions, such as cancer, diabetes and obesity.

Researchers are interested in the way immune cells fuel their activity using energy sources, such as sugars, proteins, and fats. The intersection between metabolism and immunity is often called immunometabolism. It’s a hot research topic.

One research group, which contributed to the article on which this blog was based, is currently studying how immunity cells of pregnant women differ from those of non-pregnant women in their energy use. These changes are being tracked across all three trimesters to determine whether the body’s nutritional intake can affect immune responses.

Last Thoughts: The hidden intelligence of the body

The term “pregnancy” is often used to describe a physical condition. It’s something that just “happens”. The more we know, the clearer it is that pregnancy can be viewed as a masterclass of biological intelligence.

Your body doesn’t only support a baby. It’s remodelling – rewiring the immune system and tweaking energy processing.

While the attention is often focused on the baby, the changes in the mother’s life are equally important and deserve equal attention.

If you are pregnant, plan to be or just curious, stop and marvel at the amazing things your body can do. Not only is it growing life, but also innovating, adjusting, and revealing secrets that could one day help heal diseases beyond the nursery.