Usually worsen. The hormonal changes combined with pressures internally from the baby cause more venous hypertension in your legs. Using medical support stockings, properly fitted as well as elevating your legs when possible through the pregnancy. Some start with knee high support if there are no previous bulging veins around the knees and progress to thigh high 20 mm hg support. Please see a phlebologist.
They get worse. Varicose veins are dilated veins in the legs. With pregnancy, all veins get dilated so varicose veins will get worse. They are not dangerous but there can cause aching in your legs or itching and burning. Using support hose can decrease the aching. Elevating your legs, icing them or soaking in a cool bath or pool can provide temporary relief of symptoms.
Not always. Varicose veins can get worse with pregnancy but not always. Studies give us different answers about that. Some say they do, some say they don't. Unfortunately, compression stockings probably won't keep you from getting varicose veins during pregnancy but they will help with swelling and generally make your legs feel better if you have varicose veins and are pregnant. A v2 supporter might help too.
Worsen. Pregnancy caused several changes in the body including hormonal, increased blood volume and weight gain. These factors together with the enlarging uterus result in increased venous backpressure which leads to venous hypertension and worsening varicose veins. You should see a vein specialist during your pregnancy who will also follow you post delivery.