Overall, females tend to get spider veins (pregnant or not), more often than their male counterparts. While men are still susceptible to the condition, as both genders produce the progesterone hormone, enhanced levels of this hormone can cause spider veins. Women tend to produce more progesterone than men, which is why they are likelier candidates for spider veins.
A natural hormone within the body that maintains multiple (vital) organs, progesterone also aids in the relaxation of blood vessel walls. When the walls relax, spider veins pop up, as this occurs when they weaken. When blood flows within a person’s body, it places pressure on the blood vessel walls, thus causing a spider vein to form.