Babies born to mothers with PCOS and obesity are smaller in size

Norwegian University of Science and TechnologyNov 5 2024

Women with polycystic ovary syndrome (PCOS) and obesity are at a higher risk of giving birth to smaller babies in terms of birth weight, length, and head circumference, according to a recent study conducted at the Norwegian University of Science and Technology (NTNU).

One in eight women is affected by the hormone disorder PCOS. Common characteristics are elevated levels of male sex hormones, infrequent or irregular menstrual periods, and the formation of small cysts on the ovaries.

In the study, 390 children born to women with PCOS were compared to around 70,000 children from the Norwegian Mother, Father and Child Cohort Study (MoBa) (See the fact box.)

The researchers found that on average, the babies born to mothers with PCOS weighed less, were shorter, and had a smaller head circumference at birth. This was particularly the case when the mothers were obese, meaning they had a BMI over 30.

Co-occurrence of PCOS and obesity has the worst impact.

In women of normal weight who have PCOS, we only find that their children have a lower birth weight compared to women who do not have PCOS. It is the group of children born to mothers with obesity that stands out the most. These babies have lower weight, shorter stature and a smaller head circumference. Obesity places an additional burden on mothers who have PCOS and their children."

Professor Eszter Vanky at NTNU's Department of Clinical and Molecular Medicine

PCOS is a disease that follows women throughout their lives and can trigger various metabolic diseases and challenges such as diabetes, high blood pressure, and obesity. Women with PCOS are generally more likely to develop overweight and obesity.

"What is unusual is that women who are generally overweight and gain a lot of weight during pregnancy usually have an increased risk of giving birth to large babies. This also applies to women who develop gestational diabetes. On average, women with PCOS have higher BMIs, gain more weight during pregnancy, and 25 per cent of them develop gestational diabetes. However, the outcome is the opposite: these women give birth to babies who are smaller than average. We still don't know why, but we see that the placenta is affected in these women," said Vanky.

Placenta in overdrive

The newly qualified doctors Maren Talmo and Ingvild Fløysand have carried out the study as their master's thesis, with Eszter Vanky and Melanie Rae Simpson as their supervisors. Talmo explains that even though the placenta in these women is smaller in size, it seems to deliver more nutrients relative to the baby's body weight compared to a normal placenta. Vanky describes it as a placenta in overdrive.

"The placenta delivers nutrients to the baby through the umbilical cord. In women with PCOS, we see that the placenta is generally smaller in size. At the same time, it must provide everything the baby needs, so it has to work very hard to meet these demands. Sometimes, however, the placenta can't keep up, which can lead to placental insufficiency and, in rare cases, foetal death."

The researchers do not know why this is the case.

"There are many hypotheses, but I don't think anyone has a definitive answer yet. Previously, we thought the cause was linked to the high levels of male sex hormones, but we have not been able to fully connect the two. We also know that women with PCOS have a slightly different immune profile during pregnancy."

Follow-up during pregnancy

The researchers believe this is important knowledge both for the women affected and for healthcare professionals.

"A newborn baby is not a blank slate. Much of our long-term health is established in the womb. Genes play a role, but also what we are exposed to during the foetal stage and early in life," said Vanky.

The NTNU researchers now want to learn more about what happens to the children's health.

"What are the consequences of the mother's PCOS diagnosis for the child? Is there anything that can be done before or during pregnancy so that expectant mothers with PCOS do not gain too much weight? Can follow up and good glucose regulation be provided so that the child gets the best outcome possible? All this depends on knowing more about the mother's situation," said Vanky.

Affected throughout life

The NTNU researchers have also followed up on some of the children when they reached the age of 7 years.

"We saw that the children born to mothers with PCOS generally had more central obesity, meaning they were larger around the waist," said Vanky.

Other studies have shown that children born to mothers with PCOS are at higher risk of developing overweight and obesity at a young age. Research has also shown that low birth weight is linked to the development of type 2 diabetes and cardiovascular disease later in life.

"We see differences in children as early as 7 or 8 years old, where children born to mothers with PCOS have a larger waist circumference and higher BMI. They bear small signs that their mother has PCOS. It may therefore be an advantage to know about this so we can provide guidance on lifestyle and diet," said Vanky