Researchers found that 93 percent of the women in the study breast-fed their baby in the first week after birth. However, women who had an epidural were significantly more likely to have difficulty breast-feeding during the first few days after delivery and to breast-feed less often than other women.
At 24 weeks, 72 percent of women who did not have an epidural were breast-feeding, compared with 53 percent who received pethidine or epidurals containing bupivacaine and fentanyl (an opioid).
Pat O'Brien, a spokesman for the Royal College of Obstetricians and Gynaecologists, said it was possible that fentanyl had an effect on the baby.
But he added: "There are other factors which may explain this link, including that if a woman chooses not to have an epidural, she may also be more motivated to persevere with breastfeeding.
"Also, a lot of those women who had epidurals also went on to have Caesarean sections which - unless you have a lot of support - make it difficult to breastfeed because it's harder for women to pick their babies up."