In normal pregnancies, blood histamine concentration remains within normal values; however, the serum histaminolytic activity is increased. Histamine is mainly produced by mast cells, platelets, basophils, neurons and enterochromatin cells, where it is stored and released when required. Reduced DAO activities have been found in high-risk pregnancies. Lower DAO activity has been associated to miscarriage, fetal demise, preeclampsia, low birthweight and preterm birth. The placenta is very rich in DAO activity and is the principal source of increased histaminolytic activity in normal pregnancies. First-trimester screening for preeclampsia (PE) is a routine screening which is performed in the first trimester. Women with a positive result are at a greater risk of PE but also other pregnancy complications such as stillbirth, preterm birth and low birthweight. These cases are prescribed aspirin until term. This intervention has demonstrated to significantly reduce the risk of PE and other complications. Unfortunately, aspirin does not avoid all cases with adverse outcomes, indicating that additional mechanisms may be involved in the development of such pregnancy complications, such as DAO decreased activity.