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How Hormones Influence Fetal Development

Once a woman becomes pregnant her body goes through many changes: her hormone levels increase, her feet swell, and her belly grows to name a few. Over the course of her pregnancy she will have an increased amount of estrogen, progesterone, insulin, insulin-like growth factors, glucocorticoids, and thyroid hormones. 

While hormones often get a reputation for being the main cause of a woman’s moodiness during pregnancy, they each have an important role to play to help the fetus develop and to help the mother’s body change and adjust to the changes. 

Some of the ways that hormones help the mother, and by extension the child, is they ensure that her body doesn’t attack the fetus when it’s just forming, enable her uterus and other body parts to grow and stretch to accommodate the growing child, help her cope with labour, and help her body produce milk for the child.

These six hormone families are equally important for the fetus’s development. They work together, and sometimes in opposition, with the other hormones to provide your unborn child with the right amount and right kind of nutrients. Some, like insulin and cortisol, play an important part in the baby’s size. Others, like the thyroid hormones, help the fetus’s brain develop and begin to function. Still others help the fetus’s bones grow along with everything else your unborn child is doing.

How exactly do hormones help the fetus develop? Well here is how these six different kinds of hormone families work together to help the fetus grow into a healthy child. We’re going to start with the two most common hormones in relation to women and pregnancy: estrogen and progesterone.

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7  Estrogen and the Fetal Journey

Estrogen is one of the most common hormones people mention when they’re discussing women and pregnancy. Considering how much this hormone does, that isn’t very surprising. This hormone is quite busy throughout the entire pregnancy making sure everything is running smoothly.

A mother’s estrogen levels start to increase at the beginning of her pregnancy, and they continue to increase throughout the entire pregnancy. According to an article on Healthline, one of the functions of this hormone is to help the uterus and placenta transfer nutrients from the mother to the baby. Estrogen also helps increase the mother’s blood flow so she can support her growing child.

An article on What to Expect explains that estrogen also helps the mother carry the fetus by helping her uterus grow in order to hold the increasingly larger size of the child. Estrogen also helps maintain the uterine lining, and it helps manage the other hormones required during the pregnancy. Finally, estrogen controls the fetus’s bone density and it is one of the hormones that triggers the development of the fetus’s organs.

6 The Importance of Progesterone

The other frequently mentioned hormone is progesterone. Without this hormone, the mother’s body wouldn’t be able to carry the fetus at all. This is because, as Healthline’s article points out, progesterone causes the mother’s ligaments and joints to loosen. Which means that a mother’s body can expand to help accommodate the growing fetus. In addition to helping the mother’s body stretch to hold the child, progesterone also helps the mother’s uterus grow and stretch around the fetus.

In addition to helping the placenta grow, What to Expect’s article, explains that progesterone helps keep the placenta functioning properly. Progesterone works with estrogen to make sure that the uterine lining is thick and healthy. This ensures that the lining is able to support the fetus’s changing needs.

5 Insulin and Your Fetus’ Development

A third hormone that plays an important part in the development of the fetus is insulin. Unlike estrogen and progestogen which work more with the mother’s body to deal with the growing fetus, insulin aids the fetus itself. Insulin helps the fetus’s body consume the glucose the fetus needs for all of its energy. As you can probably imagine, dividing cells and growing from the size of a seed to a watermelon takes a lot of energy.

According to the European Society for Endocrinology’s website You and Your Hormones, when a woman becomes pregnant, her body stops being as responsive to insulin. This means that her body isn’t consuming as much glucose as normal; although, she will still be consuming as much glucose as she needs. 

This extra glucose then travels across the placenta, where the fetus’s insulin works to help the child’s body use the glucose as an energy source so it can grow, or if the fetus doesn’t currently need energy, the insulin will help the glucose be saved as fat.

However, sometimes pregnant women experience gestational diabetes because their bodies are absorbing even less glucose than they should be. When this happens the fetus’s insulin still helps the child absorb all of the extra glucose. This can cause the fetus can grow too much, which means that the mother and child are more likely to need medical intervention during labour.

4 Insulin-Like Growth Factors

A fourth kind of hormone that plays an important role in the fetus’ development are the insulin-like growth factors. Insulin-like growth factors aren’t actually a single type of hormone, rather they are a family or collection of hormones that, you might be surprised you to hear, act similarly to insulin and help the fetus grow. 

The European Society for Endocrinology’s article “Hormones and Foetal Growth,” states that several different studies have found a connection between the two insulin-like growth factors IGF-I and IGF-II and the child’s weight at birth.

Hormones help your baby to grow

These two hormones work closely together to ensure that the placenta is giving the fetus the right nutrients and the right amount of those nutrients. IGF-I has several different functions. One function is to determine which nutrients are currently present in the mother’s body and another one is to figure out what nutrients the fetus currently needs. Then, once IGF-I has that information it allows the correct types of nutrients to pass through the placenta, so that the fetus can be nourished and grow.

IGF-II on the other hand, has a more peripheral effect on the fetus’s growth, since its function is to control the growth of the placenta. By stimulating the growth of the placenta, IGF-II helps the fetus grow, because it enables the placenta to transfer larger amounts of nutrients to the fetus as the demand for them grows. 

3 How Glucocorticoids Are Important to Your Fetus

Another important family of hormones to the fetus’s development are the glucocorticoids, like cortisol and corticosterone. This family of hormones is also known as the steroid hormones or the stress hormones. These hormones have a very important job in the development of the fetus right at conception, because they are what prevent the mother’s body from attacking the fetus.

According to an essay by Gwen Dewar, the levels of these hormones begin to increase drastically during the second trimester. However, because women’s bodies are unable to use them, since their bodies are also creating a protein that prevents their bodies from reading the glucocorticoids, these hormones are generally unused. The amount of glucocorticoids increases again in the third trimester. 

This time, the extra hormones are used. In the third trimester, glucocorticoids help the fetus’s lungs and other internal organs develop so that the child will be viable or able to live outside of the womb.

The glucocorticoids also work in opposition to insulin and the insulin-like growth factors, because at the same time that these stress hormones are helping the fetus’s organs develop, they are also preventing the fetus from growing larger. 

While this is normally a good thing, preventing the fetus’s growth and triggering the start of organ development can cause the fetus problems if this starts too early in the pregnancy, because the fetus will think that it’s time to focus more on developing their lungs and other organs instead of growing bigger in size. This can cause the child to be born underweight, which can cause the child to have health problems growing up and to have some learning disabilities.

2 How the Thyroid Hormones Impact Fetal Development

Another hormone family that influences fetal development is the thyroid hormones. The thyroid hormones have two main functions that seem to be quite different from each other. They help with the development of the fetus’s brain, and they help the fetus turn to face the right direction for labour and delivery.

Thyroid hormones work together to help the fetus’s brain develop. They aid in the creation of neurons and myelin, which is a substance that coats the neural pathways and helps a person’s brain to function faster. According to an article by Moog NK et al., if the fetus is deprived of thyroid hormones the child will have a myriad of problems with their cognitive and motor capabilities, as well as with their hearing and speech. 

The damage caused to the fetus by a lack of thyroid hormones is greatest in the first trimester.

In addition to helping the brain develop, thyroid hormones also play a part in the baby’s position during labour. A study by Hennie A. Wijnen et al., discovered that women who had normal levels of thyroid hormones were also more likely to have a fetus that have moved into the normal presentation (head first) for labour. 

In addition to brain development and birth presentation, having a normal amount of thyroid hormones helps decrease the likelihood of miscarriage and premature delivery.

1 Why Properly Functioning Hormones Means a Healthy Baby

Sometimes when you’re pregnant you’re going to feel exhausted, and with good reason. Your body is doing so much to try and make sure that it is the most hospitable location possible for your unborn child. The six hormones and hormone families mentioned above, all play vital roles as they work to knit your child together in your womb. 

While they seem like such a small thing, without the thyroid hormones, glucocorticoids, insulin-like growth factors, insulin itself, estrogen and progestogen, your body would attack your fetus before your child gets a chance to grow, think, or breathe.

You're growing a human and that's hard work!

So the next time you feel sick, or moody, or angry at everything that moves, remember that it truly is because all of your hormones are out of whack, and that they’re fluctuating for very specific reasons. Some of those fluctuations are caused by the fetus asking for specific nutrients. Others might be because the fetus is unable to use their own hormones to perform certain tasks, since they might not have those hormones yet, or at least not enough of them. 

And while the hormones might make you feel sick or tired, those fluctuations are helping to ensure that your child has fully developed lungs, is not too big or not too small, and is in the correct position when it’s time for him or her to be born. So go ahead and relax, you and your unborn child are both working very hard for a chance to meet one another.

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