Pregnancy and Breast Cancer Risk 

Introduction

Every woman’s hormone levels change throughout her life for a variety of reasons, and hormone 

changes can lead to changes in the breasts. Hormone changes that occur during pregnancy may 

influence a woman’s chances of developing breast cancer later in life. Research continues to 

help us understand reproductive events and breast cancer risk. The National Cancer Institute 

(NCI) is currently funding research that may lead to discoveries that identify ways to mimic 

pregnancy’s protective effects and translate them into effective prevention strategies. 

Pregnancy-Related Factors that Protect Against Breast Cancer 

Some factors associated with pregnancy are known to reduce a woman’s chance of developing 

breast cancer later in life: 

• The younger a woman has her first child, the lower her risk of developing breast cancer 

 during her lifetime. 

• A woman who has her first child after the age of 35 has approximately twice the risk of 

 developing breast cancer as a woman who has a child before age 20. 

• A woman who has her first child around age 30 has approximately the same lifetime risk of 

 developing breast cancer as a woman who has never given birth. 

• Having more than one child decreases a woman’s chances of developing breast cancer. In 

particular, having more than one child at a younger age decreases a woman’s chances of 

developing breast cancer during her lifetime. 

• Although not fully understood, research suggests that pre-eclampsia, a pathologic condition 

that sometimes develops during pregnancy, is associated with a decrease in breast cancer risk 

in the offspring, and there is some evidence of a protective effect for the mother. 

• After pregnancy, breastfeeding for a long period of time (for example, a year or longer) 

 further reduces breast cancer risk by a small amount. 

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Pregnancy-Related Factors that Increase Breast Cancer Risk 

Some factors associated with pregnancy are known to increase a woman’s chances of developing 

breast cancer: 

• After a woman gives birth, her risk of breast cancer is temporarily increased. This temporary 

 increase lasts only for a few years. 

• A woman who during pregnancy took DES (diethylstilbesterol), a synthetic form of estrogen 

that was used between the early 1940s and 1971, has a slightly higher risk of developing 

breast cancer. (So far, research does not show an increased breast cancer risk for their female 

offspring who were exposed to DES before birth. Those women are sometimes referred to as 

“DES daughters.”) 

Other Breast Cancer Risk Factors Not Related to Pregnancy 

At present, other factors known to increase a woman’s chance of developing breast cancer 

include age (a woman’s chances of getting breast cancer increase as she gets older), a family 

history of breast cancer in a first degree relative (mother, sister, or daughter), an early age at first 

menstrual period (before age 12), a late age at menopause (after age 55), use of menopausal 

hormone replacement drugs, and certain breast conditions. 

Obesity is also a risk factor for breast cancer in postmenopausal women. More information 

about these and other breast cancer risk factors is found in NCI’s publication What You Need To 

Know AboutTM Breast Cancer.

Misunderstandings About Breast Cancer Risk Factors 

There are a number of misconceptions about what can cause breast cancer. These include, but 

are not limited to, using deodorants or antiperspirants, wearing an underwire bra, having a 

miscarriage or induced abortion, or bumping or bruising breast tissue. However, none of these 

factors has been shown to increase a woman’s risk of breast cancer. In addition, cancer is not 

contagious; no one can “catch” cancer from another person. 

Preventing Breast Cancer 

There are some things women can do to reduce their breast cancer risk. 

Because some studies suggest that the more alcoholic beverages a woman drinks the greater her 

risk of breast cancer, it is important to limit alcohol intake. Maintaining a healthy body weight is 

important because being overweight increases risk of postmenopausal breast cancer. New 

evidence suggests that being physically active may also reduce risk. Physical activity that is 

sustained throughout lifetime or, at a minimum, performed after menopause, may be particularly 

beneficial in reducing breast cancer risk. Eating a diet high in fruits and vegetables, and energy 

and fat intake balanced to energy expended in exercise are useful approaches to avoiding weight 

gain in adult life. 
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Detecting Breast Cancer 

A woman can be an active participant in improving her chances for early detection of breast 

cancer. NCI recommends that, beginning in their 40s, women have a mammogram every year or 

two. Women who have a higher than average risk of breast cancer (for example, women with a 

family history of breast cancer) should seek expert medical advice about whether they should be 

screened before age 40, and how frequently they should be screened. 

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Related National Cancer Institute (NCI) Materials

• National Cancer Institute Fact Sheet 3.75, Abortion, Miscarriage, and Breast Cancer Risk 

http://www.cancer.gov/cancertopics/factsheet/Risk/abortion-miscarriage 

• What You Need To Know AboutTM Breast Cancer

http://www.cancer.gov/cancerinfo/wyntk/breast 

• General Information About Breast Cancer 

http://www.cancer.gov/cancer_information/cancer_type/breast/ 

• Summary Report: Early Reproductive Events and Breast Cancer Workshop 

http://www.cancer.gov/cancerinfo/ere-workshop-report 

NCI Resources

Cancer Information Service (toll-free)

 Telephone: 1–800–4–CANCER (1–800–422–6237) 

 TTY: 1–800–332–8615 

Online 

NCI’s Web site: http://www.cancer.gov 

LiveHelp, NCI’s live online assistance: 

https://cissecure.nci.nih.gov/livehelp/welcome.asp 

 

This fact sheet was reviewed on 4/30/08