Why is it that obstetricians now cut in this seemingly more damaging direction?

The rectus abdominus muscle is the main muscle of the abdominal region. Until the early 1980's, women who gave birth via Caesarian section were opened up with a longitudinal cut down the midline of their abdomen. Since then there has been a shift for C-section incisions to cut across the bottom of the belly (i.e. right to left). Cutting a muscle perpendicular to the “grain” is much more damaging to it than a cut along the length of the muscle (“with the grain”).