Introduction

Nipple discharge during pregnancy is a common and normal event that can have a physiological or pathological cause. It is important to be aware of the different types and the appearances of normal and abnormal nipple discharge, because increased awareness can enable early detection and timely treatment of breast cancer and other breast conditions.¹⁵

This article will focus on nipple discharge during pregnancy, so it won’t cover galactorrhea or duct ectasia. While both of these conditions cause nipple discharge, they are not strongly associated with pregnancy. 

Breast anatomy

For those assigned female at birth, the breasts, located on top of the pectoralis major muscle, are made up of milk-producing glandular tissue, fatty tissue, and connective tissue, as well as blood vessels, nerves, and lymph nodes.¹

Each breast is composed of 15 to 20 lobes, and each lobe has smaller structures called lobules, which have glands that produce milk. The lobes and lobules are connected by ducts, which enlarge to form the lactiferous sinus, where milk collects before being released through the nipple. The nipple is a raised conical region at the centre of each breast and is surrounded by a darker area of skin called the areola.² 

What is nipple discharge?

Nipple discharge refers to the release of fluid from one or both of the nipples that occurs spontaneously or following the handling of breast tissue. 

Nipple discharge is not uncommon, with over 80% of females experiencing an episode of nipple discharge during their lives. Nipple discharge is also the third most common breast symptom (following breast pain and palpable breast lump), which prompts people to seek medical treatment.⁴

Types of nipple discharge

There are different types of nipple discharge, including:⁴

• Lactational nipple discharge is the normal production of milk (i.e., lactation) that occurs during pregnancy, which may continue for up to one year post-partum
• Physiological nipple discharge is benign (not harmful or cancerous), usually bilateral (affecting/occurring in both nipples), and the discharge is a white, green, or yellow colour. Physiological nipple discharge is linked to nipple squeezing and can be caused by hypothyroidism or medication
• Pathological nipple discharge is spontaneous, unilateral (affecting/occurring in one nipple), and a clear, serous, or bloody discharge. Pathological nipple discharge is often caused by a benign lesion (such as duct ectasia or intraductal papilloma) or due to the presence of cancer

Normal nipple discharge during pregnancy

During the course of pregnancy, the breasts’ anatomy and functionality change in response to hormones to prepare for lactation. For instance, during the 1st trimester, an increase in oestrogen causes the ductal system to expand, while prolactin stimulates the mammary glands to produce components of milk by the 20th week of gestation.⁶

Leaking from the nipples during pregnancy is normal. The discharge may be colostrum or may occur as a result of rusty pipe syndrome.

Colostrom 

Colostrum refers to the initial breastmilk typically produced between the 12th and 16th week of pregnancy. Colostrum is a thick, white-yellow-coloured liquid which contains antioxidants, enzymes, antibodies, leukocytes, hormones, and proteins to provide nutrition, help establish a normal gut microbiome, and provide immunity to the baby.⁷ Colostrum may leak from the nipples during early pregnancy and can be expressed (manually extracted using hands or a pump) during the 3rd trimester.

Rusty pipe syndrome 

Rusty pipe syndrome is a benign physiological condition which causes painless bloody nipple discharge in pregnant and postpartum primiparous (pregnant or giving birth for the first time) women. The nipple discharge, which is often bilateral, can be orange, brown, pink or rust-coloured, resembling water from a rusty pipe (hence the name rusty pipe syndrome). This discolouration occurs as a result of colostrum mixing with blood leaking from damaged capillaries within the breast.^9,10

While rare, rusty pipe syndrome typically occurs during the early postpartum period, with discoloured milk appearing during the first few days of breastfeeding. This condition is self-limiting, often resolving spontaneously within 3 to 7 days after lactation starts, although it can also continue during the first weeks of lactation.^9,10

Abnormal nipple discharge during pregnancy

Abnormal nipple discharge can have different appearances, including: ⁵

• Milky/white
• Multicoloured and sticky
• Purulent (containing pus with white blood cells seen with microscopy)
• Watery (colourless)
• Serous (containing/resembling serum, light yellow colour)
• Serosanguinous (containing/resembling serum and blood, pink colour and red blood cells seen with microscopy)
• Bloody  

Potential causes of abnormal discharge during pregnancy

Infection

Mastitis is the inflammation of the breast and causes the breast to appear red and swollen and feel tender, hot, and painful. You may feel a wedge-shaped lump in your breast and feel a burning sensation, which may be constant, or when breastfeeding. You may also experience flu-like symptoms, including a high temperature, aches, tiredness and chills. Nipple discharge as a result of mastitis may appear white with streaks of blood. 

Lactational or puerperal mastitis refers to mastitis that occurs during pregnancy, lactation and weaning and can be caused by milk stasis (build-up and stagnation of milk within the breast) or a Staphylococcus aureus infection.¹¹

A breast abscess is a collection of pus within the breast that can form as a complication of mastitis and may cause purulent nipple discharge.¹¹

Breast cancer

Pregnancy-associated breast cancer is breast cancer that is diagnosed during pregnancy or within the first postpartum year and is the 2nd most common malignancy associated with pregnancy, affecting approximately 1 in 3000 pregnant women.¹² Cancer can cause watery, serous, serosanguinous, or bloody nipple discharge.⁵

Paget’s disease of the nipple is a rare condition associated with breast cancer, which can cause bloody nipple discharge. While Paget’s disease of the nipple is commonly reported in postmenopausal or older women, it can occur in lactating women. Nipple eczema, which also causes nipple discharge, frequently develops during breastfeeding and looks very similar to Paget’s disease of the nipple.¹⁵

Carcinoma causes approximately 10% to 15% of pathological nipple discharge cases, with unilateral persistent blood-stained (often bright red) nipple discharge being a symptom of ductal carcinoma in situ.^13,14

Intraductal papilloma 

An intraductal papilloma is a benign polypoid lesion (a wart-like growth) comprising 35% to 56% of lesions that cause pathological nipple discharge.^4,14 Intraductal papilloma can cause unilateral serous, serosanguinous, and bloody nipple discharge.^4,5

Medication

Certain medications that you may take during the course of your pregnancy or, in general, can cause physiological nipple discharge. Examples of such medications include:¹⁶

• Methyldopa, an antihypertensive medication, is used to treat gestational hypertension and chronic hypertension in pregnancy 
• Metoclopramide, a gastrointestinal agent, is used to treat nausea and vomiting in pregnancy
• Psychotropic medications, including selective serotonin reuptake inhibitors and antipsychotics

Galactocele

Galactoceles are benign milk-containing cysts that form following persistent lactiferous duct obstruction and cause milky nipple discharge.¹⁷

When to seek medical attention

You should see your doctor if you experience nipple discharge from one or both of your nipples. It may be that the cause of nipple discharge is benign, but it is always important to get it seen by a doctor to determine the underlying cause and rule out breast cancer. 

Diagnostic procedures and tests

In order to determine if the cause of nipple discharge is physiological or pathological, your doctor will need to consider your past medical history and findings from a physical examination. 

Your doctor will ask you lots of questions about your health to establish a thorough medical history. They will also conduct a physical examination, during which they will feel for the presence of a palpable mass, inspect the nipples using a magnifying lamp, observe whether the nipple discharge is unilateral or bilateral, and note the colour of the discharge.⁴

Physiological nipple discharge typically does not require imaging; however, pathological nipple discharge does require imaging to determine the presence of malignancy.¹⁸ There are a variety of imaging techniques used to examine the breasts and nipples. These imaging techniques include: ^4,18

• Mammography
• Digital breast tomosynthesis
• Ultrasound
• Galactography (use of X-ray to view ducts)
• Ductoscopy (a minimally invasive procedure to view ducts)
• Nipple discharge cytology
• Magnetic Resonance Imaging (MRI)
• Contrast-enhanced mammography
• Surgery such as microdochectomy 

Treatment options for abnormal discharge

The treatment you receive depends on the underlying cause of nipple discharge. Table 1 lists different causes of nipple discharge during pregnancy and the recommended treatment(s). 

While radiotherapy can be used to treat cancers such as breast cancer, it is not used during pregnancy as it involves an increased risk of harm to the fetus.¹²

Table 1: The different causes of nipple discharge during pregnancy and the recommended treatment. 

Preventive measures and self-care tips

• There are helpful guides on breastfeeding and expressing breast milk, which can help you take care of your breasts and nipples during pregnancy and lactation  
• Avoid wearing tight-fitting bras and consider wearing a maternity/nursing bra to support growing breasts during pregnancy
• Use maternity breast pads or nursing pads to absorb milk leaking from your nipples

Summary

• For people assigned female at birth, the breasts consist of milk-producing glandular, fatty, and connective tissues and the structure and function of the breasts change with pregnancy to enable lactation
• Nipple discharge refers to the release of fluid from the nipple(s), which can be categorised as lactational, physiological and pathological and has different colours/appearances
• Normal nipple discharge may be colostrum or due to rusty pipe syndrome
• Abnormal nipple discharge can be caused by infection, cancer, non-cancerous lesions, and certain medications
• Diagnosis of the underlying cause of nipple discharge involves your medical history, physical examination and imaging techniques
• Treatment of nipple discharge depends on the underlying cause and can include surgery and medication