Skin changes during pregnancy - melanocytic naevi

What are melanocytic naevi?

Melanocytic naevi (also known as moles) are normal overgrowths on your skin of melanocytes. Melanocytes are cells on your skin that produce pigment. Most people have moles. Usually, you are not born with moles, but they develop on your skin during childhood and adolescence. By the age of 15 years, Australian children have an average of 50 or more moles.

Most moles are brown but can vary in colour from pink to black. Moles are usually flat, relatively even in colour and regular in shape. Some moles are raised, and these moles are usually light in colour and soft to touch.

In some women, moles may change during pregnancy. More than 1 in 10 women have moles that get darker or larger, particularly in the first trimester. It is also common for naevi on the breasts and abdomen (tummy) to get bigger due to skin stretching.

What causes melanocytic naevi?

The number of moles you develop is usually set by your genes. You inherit genes from your parents that make you more or less likely to develop naevi. Sunlight is another important cause of moles. Exposure to sunlight during your childhood and teenage years makes you more likely to develop naevi.

During pregnancy, skin stretching and hormonal changes can make your naevi appear darker or larger.

Can melanocytic naevi be prevented?

Moles can’t be entirely prevented as your tendency to develop moles is largely genetic. However, sunlight exposure, especially during childhood and adolescence, contributes to the development of moles. Protecting your skin from the sun starting from a young age can reduce the number of moles you develop.

Will melanocytic naevi affect my pregnancy?

Most people have melanocytic naevi. While your naevi may change in appearance or size during pregnancy, this is usually not worrying and should not affect your pregnancy. However, if you have moles and are pregnant, it is important to monitor your moles and make sure that they are not developing any features that may be worrying. Melanocytic naevi have the potential to develop into melanoma, a type of skin cancer. If you notice that any of your moles have changed during pregnancy, show them to your doctor who will assess and monitor them, using the ABCDE diagnostic criteria for melanoma.

Your doctor will check your naevi, looking for:

• Asymmetry
• Border irregularity
• Colour variation
• Diameter of more than 6 millimetres (mm)
• Elevation or Evolution (change in size, shape or colour)

If your doctor is concerned about any of your naevi, they will take a biopsy (a sample of the mole) and send it to the lab to determine whether the mole is cancerous or not. If the lesion is cancerous, your doctor will refer you to specialist doctors to ensure the best possible outcome for you and your baby.

How are melanocytic naevi treated?

Usually, melanocytic naevi do not need treatment. A benign (non-cancerous) naevus can be removed for cosmetic reasons or if it is irritating. If there is concern that a mole may be cancerous, if should be removed in its entirety with a 2mm border and sent to a pathology laboratory to check if it is cancerous.

Will melanocytic naevi affect my baby?

Melanocytic naevi will not affect your baby. In the unlikely event that one of your naevi become cancerous during your pregnancy, and you develop melanoma, it is exceedingly rare for the melanoma cells to cross the placenta and effect your baby.

When should I see my doctor about melanocytic naevi?

You should see your doctor about your naevi if you see that a mole is asymmetric, the border is irregular, there is a colour difference within the mole or the diameter (size) of the mole is more than 6mm. You should also see a doctor if one of your moles is elevated or you notice a change in the size, shape or colour of the mole.

Will I still have melanocytic naevi after I’ve had my baby?

Melanocytic naevi do not disappear after giving birth. Just like you most likely had moles before to becoming pregnant, you will continue to have moles after your baby is born.

Will I have melanocytic naevi in future pregnancies?

Melanocytic naevi are extremely common in the general population. Most people have moles, even if they have never been pregnant. It is likely that you will have moles in future pregnancies, just like you most likely had them before becoming pregnant. In your next pregnancy, it is possible that some of your moles will become darker or larger due to hormonal changes.