Background: Lactational amenorrhoea, an established natural method of contraception, requires proper knowledge and implementations for getting desired effect. Aim: to find out the magnitude of unintended pregnancy during lactational amenorrhoea. Material and methods: A cross–sectional descriptive study was conducted in department of Obstetrics & Gynaecology and Radiodiagnosis, Bankura Sammilani Medical College & Hospital from March to May’2018 involving a pseudocohort of 2160 lactating women with complaints of lower abdominal discomfort, prolong ammenorhoea. Data were collected via interview using predesigned questionnaire. Result: Overall, 1.39% of the attendees were diagnosed to sustain unintended preganancy during lactational ammenorhoea with 1.24%, 1.29% and 30.77% among the women exclusively breastfed their babies up to six months, 7 months and 8 months respectively. More than half (56.67%) of the pregnancy was found to occur beyond one year post–partum. Conclusion: LAM requires an effective counseling to be used as a cost–effective transitional contraceptive.