Previously, we reported recessive gene(s) that terminate fetal development on swine chromosome (SSC) 6 between SW855 and SW122. The affected alleles originated from a Göttingen miniature pig used for construction of a Göttingen miniature pig x Meishan resource population. However, it is not known when the gene(s) are activated during fetal development, which is one of the important factors in selecting candidate genes responsible for fetal death. In the present study, a second swine population consisting of 159 progeny was produced by mating pigs carrying the deleterious allele(s). This population allowed us to narrow the genetic region harbouring the affected gene(s) and to demonstrate that the region was confined between RYR1 and SW782 (5.7 cM on the National Institute of Animal Industry (NIAI) map and 100 cR on the INRA/University of Minnesota porcine radiation hybrid panel map). In order to determine when the affected gene(s) are activated and in turn terminate fetal development, embryos produced in the second population were collected at several development stages and genotyped for markers in the region. Genes in the homozygous state affected embryo development between 9 and 11 days post-coitus.