Since a lot of women develop heavy front thighs due to sport activities like swimming, running etc. which cause the front pants legs to be too snug at the upper thighs.
Measure your thighs at 2 inches below the crotch, next measure the pants pattern front and back at the same height 2 inches below the crotch the total width of your pattern must be your thighs width + 2-3 inches ( 5-7,5 cm)
For example, if your patternwidth is 1 inch short in width you can add that amount at the front pattern.
If your pants pattern has a crease line you can start from there , if your pattern doesn’t have a crease line, draw one see step 1 at the diagram.
Draw a horizontal line at the front pattern, 1 inch below the crotch line from side seam to inner leg seam.
Measure the space between this new line till knee height and divide this in 2 and draw a horizontal line halfway.
Cut the front crease line from the waistline towards the knee and cut open the 3 new horizontal lines. See step 2
Add a piece of paper under the slashed pattern and spread the pattern parts like the example diagram see Step 3
Draw a new crease line from the knee up to the waist, add at both sides of the new crease line ½ inch at upper thigh .The side seams inner and outer leg are now spread for about 1/8 -1/4 inch. You can ease in those inches (1/8 till ¼ inch) so the front side seam fits the backside seam again.
If your front pattern needs more than 1 inch then I would suggest to use a larger size pattern because otherwise the space at inseam and side seam lines are increasing too much and easing in will not be possible anymore.