The genetic improvement of reproductive traits is challenging in swine. The use of vulva score (VSC) assessed at 15 weeks of age on gilts has been previously proposed as an indicator trait of reproductive performance in sows. However, the genetic basis of vulva size (VS) traits and its genetic relationship with reproductive performance is unknown. Therefore, in this thesis, we estimated genetic parameters and performed genome-wide association study for VS traits and VSC, performed genomic prediction for VS traits, and associated VSC with first-parity performance, in different populations of purebred gilts. We observed moderate to high heritability for VS traits, ranging from 0.08±0.06 (vulva width, VW) to 0.55±0.10 (vulva height, VH), with traits having very high genetic correlations with each other. QTL were identified in both breeds, on chromosomes 2, 7, 8, and 10 for Landrace, and 1 and 5 for Yorkshire. Genomic prediction accuracies were moderate in Landrace, with 0.61, 0.30, and 0.52, and low in Yorkshire, with 0.07, 0.11, and 0.07 for VA, VH, and VW, respectively. In a different study, we evaluated the effect of VSC, using a three-point scale: small (VSC-S), medium (VSC-M), and large (VSC-L), on reproductive performance from three farms. For farm 1, VSC were not associated with reproductive traits, though general means were favorable. For farm 2, VSC-L and VSC-M were associated with lower (P=0.05) total number born (TNB; 11.37±0.20) than VSC-S (12.94±0.82). For farm 3, VSC-L and VSC-M were associated with greater (P=0.06) TNB (12.03±0.15) than VSC-S (11.70±0.16), greater (P=0.02) number of piglets born alive (NBA; 11.34±0.13) than VSC-S (10.92±0.14), and lower (P=0.03) number of mummies (MUM; 0.09±0.01) than VSC-S and VSC-M (0.15±0.01). Heritability estimates of VSC as a quantitative trait (VSCq) were 0.20±0.10, 0.09±0.09, and 0.34±0.05, and of VSC as a categorical trait (VSCc) were 0.13±0.07, 0.07±0.07, and 0.20±0.03 for farms 1, 2, and 3, respectively. Moderate genetic correlations between VSC with reproductive traits were found for TNB (0.61±0.47) and MUM (0.69±0.47) for farm 1, for number of services until first farrow (NS; 0.69±0.38) and unique service with successful first farrow (SFS; -0.71±0.38) for farm 3. Multiple genomic regions associated with VSCc were identified. Of these, a QTL located on chromosome 3 at 33-34 Mb accounted for about 7.1% of the genetic variance for VSCc and VSCq. This region harbors the gene PRM1 that has been associated with early embryonic development in pigs. These results indicate that genetic selection and genomic prediction for changes in VS or VSC is possible, and that genetic selection for increased of VSC should resulted in increased NBA and TNB, and lower MUM. Results, in general, differed depending on the breed used and on the farm. Therefore, in this thesis we suggest that VSC may be predictive of first-parity reproductive performance in sows.