The first part of the thesis comprises a literature review on placental development with focus on trophoblast function and homeobox genes. Homeobox genes belong to a large family of transcription factors that control proliferation, invasion, migration and differentiation. Trophoblast dysfunction is thought to be a major factor in defect placentation and thus important in a number of clinically complicated pregnancies. The second part of the thesis relates to a morphological and immunohistochemical pilot study on remodelled spiral arteries in the placental bed from first trimester pregnancies. Remodelled spiral arteries were identified morphologically in archive curettage tissue material from Ullevål University Hospital in normal and pathological first trimester pregnancies (therapeutic abortions and spontaneous or missed abortions). The remodelled spiral arteries were identified morphologically in routine stained sections and immunohistochemically by means of protein markers to trophoblasts (CK7) and smooth muscle cells (actin). In an immunohistochemical pilot study at Pregnancy Research Centre at the University of Melbourne we tested the quality of two laboratory made antibodies against the proteins coded for by homeobox genes HLX1 and DLX4 on formalin fixed, paraffin embedded archive tissue. The aim was to explore the protein expression of these two important homeobox genes on the archive material from the normal and pathological first trimester pregnancies. Unfortunately, the antibodies were not found suitable for this use. The problems and pitfalls in protein expression studies on tissue material (immunohistochemistry) are discussed.