Are There Breast Cancer Risks Linked to Pregnancy or Abortion?

Doctor and pregnant woman looking at digital tablet. Credit: Hero Images / Getty Images

Pregnancy is a time when a woman’s breasts develop more fully and she is exposed to hormone changes. Studies demonstrate a woman’s risk for breast cancer is related to exposure to hormones, which are produced by her ovaries. Factors that increase the time and levels of exposure to her ovarian hormones, which are responsible for stimulating cell growth, are associated with an increase in her potential breast cancer risk. These factors include beginning menstruation at an early age and beginning menopause at a later age. Other risk factors include later age at first pregnancy and never having given birth.

Both the age when you give birth to your first child and the number of children you give birth to affect your risk. Numerous studies have determined that a woman who doesn’t become pregnant before age 30 and carry a child full-term has a higher risk of breast cancer than a woman who gives birth before she is 30 years old.

Breast cells developed in the teen years are immature and very active until a woman has her first pregnancy that results in a full-term birth. This first full-term pregnancy results in breast cells fully maturing and growing more regularly. This is considered to be the primary reason why pregnancy reduces the risk of breast cancer. The absence of menstruation while pregnant reduces the number of menstrual cycles in a woman’s lifetime, which may be another reason why having an early pregnancy seems to reduce the risk of breast cancer.

When a woman has her first child at a later age, she has an increased risk for breast cancer compared to a woman who has her first child at a younger age. Having a first pregnancy at 35+ years old, makes a woman 40 percent more likely to get breast cancer than a woman who had her first child before she was 20 years of age.  

Research also shows that the more full-term births a woman has, the lower her breast cancer risk. For a woman who has never given birth, her risk of breast cancer is only slightly higher when compared to women who have had more than one child. But, a woman who is over 35 and gives birth has a slightly higher risk compared to a woman who never had a child.

Additional Pregnancy Factors Associated with Increased Breast Cancer Risk

  • Recent childbirth: Women who've recently given birth are believed to have a short-term increase in their risk for breast cancer. The reason for the temporary increase is not really known. One theory is that it may be the effect of high levels of hormones on microscopic cancers, or even the fast growth of breast cells while pregnant.
  • Taking diethylstilbestrol (DES) while pregnant: It has been almost 50 years since DES has been prescribed for pregnant women in the U.S. Studies found that this synthetic estrogen caused women, who took it during their pregnancies, to be at a slightly higher risk for breast cancer than women who didn’t take DES during pregnancy. This elevated risk carried over to their daughters who now may also have a slightly higher risk of developing breast cancer, after age 40, than women who were not exposed to DES while in their mothers’ wombs.

Is Abortion a Breast Cancer Risk?

There were a few studies in the mid-1990s that suggested an induced abortion was associated with an increased risk for breast cancer. These studies had design flaws. The studies relied on the participants self-reporting their medical histories which can create inaccuracies.

However, prospective studies, which are much stricter in design, have shown no association between induced abortion and breast cancer risk. In 2009, the Committee on Gynecologic Practice of the American College of Obstetricians and Gynecologists reached a consensus that “More rigorous recent studies demonstrate no causal relationship between induced abortion and a subsequent increase in breast cancer risk.” Findings from these most recent studies state that:

  • Women who have had an induced abortion have the same risk of breast cancer as other women.
  • Women who have had a spontaneous abortion, otherwise known as a miscarriage, have the same risk of breast cancer as other women.
  • Cancers other than breast cancer also appear to be unrelated to a history of induced or spontaneous abortion.
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  • The National Cancer Institute