Women are more susceptible to varicose veins because the valve leaflets become softer and the vein walls more distensile due to the cyclical influence of the female sex hormones, oestrogen and progesterone periodically throughout the menstrual cycle. 
Pregnancy will commonly provoke the development of new varicose veins and also aggravate varicose veins that were present before pregnancy. As the pelvic pressure increases with the growth of the baby, the obstruction begins to cause back pressure on the veins in the lower limbs causing increasing congestion. The higher the number of pregnancies, the greater the risk is for the mother to develop varicose veins. Another factor leading to the increased risk of varicose veins is that the circulating blood volume in a woman as she approaches term increases by nearly 50%.
It is recommend that women consider treating there varicose veins prior to pregnancy as this will reduce the risk of their further development. 
However should you have varicose veins that develop during your pregnancy do not be too concerned as they may spontaneously regress within a few months following your delivery. Please do not hesitate to contact us a qualified sclerotherapist should you have any concerns during your pregnancy as an Ultrasound examination can provide an accurate baseline assessment if you do require treatment in the future.
1. McCausland, A.M., F. Holmes, and T. A.D., Venous distensibility during the Menstrual Cycle. Am J Obstet Gynecol, 1963(86): p. 640-645.
2. Barwin, B.N. and J.C. Roddie, Venous distensibility during pregancy determined during the menstrual cycle Am J Obstet Gynecol, 1976(125): p. 921-923.
3. van der Stricht, J. and C. van Oppens, Should Varices be Treated Before or After Pregancy Phebol, 1991(44): p. 321-326.