Structures that are 3D printed by an extrusion process have periodic geometrical heterogeneity whose influence on the final stiffness properties is not extensively discussed in the existing literature. The objective of this article is to quantify the effect of local lace geometry on the anisotropy of extrusion-based 3d printed structures. A numerical homogenisation scheme is implemented to compute an equivalent homogeneous Kirchhoff-Love plate stiffness. The methodology is applied to the parametric study of an oblong lace resulting from oriented-lace pressing. The study reveals that the bending stiffness in the two principal directions may vary by an order of magnitude for common lace geometries, even in the assumption of a perfect bound between layers. Numerical benchmarks against 3D Finite Element Analysis show that the proposed approach is accurate while significantly decreasing the number of degrees of freedom of the numerical model. Beyond understanding of geometrical defects on the overall stiffness of 3D printed structures, this approach can thus be applied for efficient structural analysis of 3D printed pieces with thousands of layers.