Scientists agree that the later a woman delays a first full term pregnancy, the greater her breast cancer risk is.

The childless woman who carries her pregnancy to term instead of choosing to abort reaps two major benefits: lower breast cancer risk and better future reproductive health.  As shown in the graph, breast cancer risk increases markedly with each passing year before the birth of a first child.

In 1983 Harvard researchers Trichopolous, MacMahon and heir colleagues reported that each one year delay before a first full term pregnancy elevated relative breast cancer risk by 3.5% (compounded).

Consider how this would affect quintuplets ('Alice', 'Beth', 'Carol', 'Diane', 'Esther') born to the same mother.  All five are first time pregnant a few days after their 17th birthday.  'Alice' has a full-term delivery but the other four women all have induced abortions.  The following table shows that relative breast cancer risks of four of these quints relative to 'Alice':

Pregnant 17 year olds 'Alice' and 'Carol' will have markedly different breast cancer risks if 'Alice' delivers a full-term baby, but 'Carol' has an induced abortion and later has a first full-term delivery at age 27.  "Carol's" increased breast cancer risk is 41% higher because the birth of her first child was delayed 10 years longer than 'Alice's', and this 41% does not include the breast cancer risk resulting from a second (debated) risk of abortion - the *independent link.

The graph shows the total increased risk resulting from abortion. It includes the effect of delaying a first full term pregnancy plus the effect of the *independent link of abortion.  As noted earlier, only the second effect is debated among scientists.

The effect of the independent link is based on the Brind/Penn State scientific review and meta-analysis of the worldwide literature published in 1996.  Dr. Brind and his colleagues conservatively estimated that the increased risk associated with the independent link to abortion was 30%.

"Carol's" TOTAL breast cancer risk is 71% higher than 'Alice's'.   
"Esther's" total breast cancer risk is 128.8% higher than "Alice's"

*The independent link between abortion and breast cancer is the only debated risk.  It addresses this question: Does an abortion leave women with more cancer vulnerable breast tissue than they had before they became pregnant?