Summarize:

Preterm labor is more common when you're delivering twins. If you notice any of the following symptoms, contact your doctor immediately. Bleeding or vaginal discharge can be a sign of preterm labor. You may also start having contractions early. Diarrhea can sometimes signal preterm labor. Preeclampsia is more common during a twin pregnancy. This is a spike in blood pressure that occurs during pregnancy. Make sure to have your blood pressure monitored throughout pregnancy to make sure it's at a healthy and safe level. Rapid weight gain or headaches should be evaluated by your doctor immediately. These can be a sign of potential complications, and indicate preeclampsia is developing. Your doctor may need to deliver the twins immediately to assure their safety.
Watch out for signs of preterm labor. Monitor your blood pressure closely. Have certain symptoms evaluated immediately.