A new study out of Denmark found that use of the metformin just before conception led to a 40 percent increase in genital birth defects.
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When we think about fertility issues, we tend to think about the body of the person carrying the baby. And because of that, there are oodles of articles and studies exploring how lifestyle choices from diet and health history, including menstrual cycles and sexually transmitted infections to stress and activity levels, can impact conception. Thankfully, science has been looking harder at other factors that can affect fertility, such as the health of sperm, particularly when medications are involved. Researchers can develop a fuller understanding of how fertility works and where it needs help by looking at both female and male labeled reproductive systems.

In a recent study in the Annals of Internal Medicine, researchers found that for parents who could produce sperm and had a type 2 diabetes diagnosis and used the drug metformin to control their blood sugar for three months before conception, there was a 40 percent increase in genital birth defects in babies assigned male at birth.

The researchers followed data from Denmark that looked at national registry information for 1,116,779 births between the years 1997 and 2016 from parents with female labeled reproductive systems under the age of 35 and parents with male labeled reproductive systems under the age of 40; however, this particular study only explored the outcomes of parents with male labeled reproductive systems.

Researchers noted that out of the 1.1 million babies born to parents with male reproductive systems and who had type 2 diabetes but did not take metformin, birth defects were 3.1 percent. However, for those who filled a prescription of metformin three months before conception, there was a linked increase of birth defects at a rate of 4.6 percent. Interestingly, siblings not exposed to metformin during pregnancy saw no effect whatsoever.

What Is Metformin and Why Is It Having a Negative Effect on Fertility?

First we need to understand diabetes.

If we zoom out and look at each of the pieces of this story, we can begin to make some sense of what these researchers are finding; that medication used to treat and control diabetes can negatively impact a healthy pregnancy.

Diabetes is a chronic condition that affects how efficiently your body can turn food into energy that you need to stay alive and thrive. When we eat food, our bodies break it down into sugar or glucose, which is sent to the bloodstream. When our bloodstream is flooded with glucose, it triggers the pancreas to release insulin.

Insulin is a naturally created hormone that acts as a liaison between glucose and cells, opening cells to allow glucose to be used as energy. But for a person with diabetes, the body either doesn't create enough insulin or can't efficiently use the insulin. Over time, too much insulin in the bloodstream can lead to severe health problems that include heart disease, vision impairment or loss, and kidney disease.

Metformin helps the body use insulin.

This is where insulin medication and metformin come into the picture. Diabetes patients can take insulin shots to help regulate their own supply of insulin, which in turn regulates blood sugar and keeps the body happy and balanced. For people with type 2 diabetes, insulin resistance is an issue. Not only does a patient need insulin shots, but they need metformin to make sure that the body can efficiently use the insulin dose.

Researchers have long known that diabetes can impair male fertility, as this study from the Asian Pacific Journal of reproduction noted in 2017, "About 90% of diabetics experience upheaval in sexual function, including a decrease in libido, impotence, and infertility."

Since studies have shown that diabetes can impair male fertility and negatively impact sperm quality, researchers looked closely at rates of birth defects in babies exposed not just to metformin but also insulin. As it turns out, only metformin was associated with a sharp increase in defects. Insulin did not show the same link to defects.

Talk to Your Doctor if You Are Trying To Conceive

So, what does this mean for diabetic parents who are trying to conceive? First of all, it is worth noting that this study out of Denmark doesn't show a complete picture, only a piece of it. There are still many questions that need to be answered in further studies, such as how glycemic regulation and medication compliance play a fertility role. The Denmark study only looked at data indicating that a prescription was filled but did not look at consistency in taking medication, dose levels, diabetes medication history, or other health-related factors.

Furthermore, there are lots of conditions ranging from socioeconomic conditions, geographical location, family genetic histories, and much more that surely play a role in fertility levels for both biological parents.

Metformin was approved for use by the U.S. Food and Drug Association in 1995, and it is widely considered a safe drug to use to control diabetes. That said, it is always wise to include a discussion with your doctors about all prescriptions you take before trying to conceive. There may be alternative medicines or practices or alterations to medication dose levels that can be safer for conception in some cases, but you must talk with your doctor first.