Introduction: Breastfeeding is the basis for an emotional connection between the mother and the child; moreover, it offers the crucial nutrients for growth and development and is a source of comfort to the child. Some mothers decide to breastfeed during the pregnancy; and some even decide for tandem breastfeeding. Purpose: The purpose of the diploma thesis is to present breastfeeding during pregnancy and tandem breastfeeding to determine the effect of it on the fetus, newborn and mother. Methods: We used a descriptive research method. We searched for the literature in the international web database CINAHL with Full TEXT, Cohrane Library, MedLine (PubMed), Science Direct, COBISS and some literature was found through a web browser Google Scholar. The publication date of the literature was not limited, due to the lack of newer research and the importance of older research. Literature searches were conducted between January and May 2018. Results: Breastfeeding during the pregnancy does not cause infant growth retardation and nor does it represent an increased risk of abortion and premature birth. The authors also state that the newborn breastfed in the tandem breastfeeding, gains weight sufficiently. They concluded that a mother who is tandem breastfeeding is not undernourished; however, she might lack some nutrients. Discussion and conclusion: Breastfeeding does not represent a greater risk to the fetus and mother, if the pregnancy is normal. However, research limitations (such as a small sample) as well as other factors affecting the course of the pregnancy must also be taken into consideration. Health workers should get guidelines for giving advice to mothers breastfeeding during pregnancy and in tandem. It is advisable to provide adequate nutrition as the pregnancy and breastfeeding require a lot of effort and energy.