The average age of new mothers is now 30.2, around four years higher than in the 1970s.
Experts say that the number of women delaying motherhood means the number diagnosed while pregnant or breastfeeding is set to rise.
‘The number of under-45s diagnosed with breast cancer is on the rise, with 5,600 cases a year as delayed pregnancies are also increasing.’
Recent research from Breast Cancer Care among 496 women aged 45 and under who developed breast cancer has found one in 10 spotted signs while pregnant or breastfeeding.
More than a third of women went through treatment when their youngest child was aged five or under. Half of those who had young children when they were diagnosed felt the biggest impact of treatment was being too ill to care for them.
Samia al Qadhi, chief executive of Breast Cancer Care, said: "Being told you have breast cancer when you have a young family is devastating.
A breast cancer diagnosis during pregnancy or soon after giving birth can mean some women find it difficult to bond with their baby."
He also explained that the feelings of guilt can be huge and they may feel they have nowhere to turn. So access to support is vital. It is vital that breast cancer units should adopt recommendations for supporting younger women with breast cancer, which include a referral to a specialist if diagnosed during pregnancy.