This suggests current recommendations for premenopausal women to wait two years after their diagnosis may be unnecessary for women younger than 45 who have localised disease.
The two-year guide is based on anecdotal evidence that considers the risk of early occurrence and the need to allow adjuvant therapy to be completed. It is likely to still stand for women with systemic disease at diagnosis or who are still receiving treatment.
The latest study involved 2,539 women aged 15-44 who were diagnosed with breast cancer between 1982 and 2000. Five per cent had at least one subsequent pregnancy by the end of 2003.
Of the 123 women who became pregnant, 16 per cent conceived within six months of diagnosis and 54 per cent within two years. Forty-four per cent went on to have a live birth.
Providing chemotherapy was not given at the time of conception or in the first trimester of pregnancy, no short- or long-term health effects were noted among children of women who conceived after diagnosis, said researchers.
Among women who conceived after their diagnosis, five-year survival was 92 per cent and 10-year survival was 86 per cent.
Analysis suggested that subsequent pregnancy improved survival, with a hazard ratio of 0.6.
While the effect was strongest for women who waited at least two years after diagnosis to conceive, a protective but non-significant effect was still noted for women who waited six months .
Lead researcher Dr Angela Ives, from the University of Western Australia in Crawley, said: ‘After the completion of their breast cancer treatment, early conception for women with localised disease and good prognosis is unlikely to adversely affect survival.
This may help women in their late 30s and early 40s who want to consider having children after their diagnosis or who find themselves pregnant, but who may not have a chance to conceive if they wait two years because of reduced ovarian function.'
‘Nevertheless, GPs should make sure to discuss the issue of conception before treatment begins.'
Women who want to start a family six months after a breast cancer diagnosis should still be referred to an oncologist and a fertility expert.