Preterm labor is when you go into labor before you are 37 weeks pregnant.1 in 10 women will experience preterm labor. Early signs of preterm labor are: frequent uterine contractions (more than 4 per hour), pressure in your pelvis, increased vaginal discharge, vaginal spotting and constant back pain. Common causes of preterm labor are stress, genital infections, bladder and kidney infections, uterine abnormalities, placental abruption and having a twin pregnancy.If you have a history of having preterm labor in a prior pregnancy or if your mother experienced it, you will have a higher chance of having it as well. If you are at a high risk of having preterm labor, your health care provider will often see you more frequently. You might be offered a test called fetal fibronectin if you are between 24 and 34 weeks gestation. It involves obtaining a sample of vaginal secretions from the upper vaginal region using a small cotton swab. If the test shows the presence of a specific protein, you may have a higher chance of having preterm labor over the next 2 weeks. On the other hand, if the protein is not detected, your chances of going into preterm labor over the next 2 weeks is very small. Less than 5 women out of a 100 with a negative test will go into labor over the next 2 weeks. Cervical length measurements using a vaginal probe ultrasound is often used to look at early signs of preterm labor. Cervical length of greater than 2.5 cm (1 in) is reassuring and preterm delivery is less likely to occur then. If you develop preterm labor you will often be treated with bedrest and medications to relax the uterus. These medications are called tocolytics. Magnesium sulfate is the most common intravenous tocolytic used for this purpose. It is only given in the hospital. It will relax all of your muscles in your body in addition to your uterus so you will feel rather weak. It will often also relax the eye muscles so you will often notice a blurred vision when on it. It is a very strong medicine, so you are watched very carefully in the hospital when you are receiving it. The most common oral tocolytic used in the United States is Nifedipine (Procardia©). Its side effects include heart burn, headaches and constipation. Oral Indomethacin (Indocin©) is also often used. Its side effects include heartburn, reversible decreased amniotic fluid and reversible changes in the baby_s heart. For these reasons, it is used very carefully and for very short times only. It is often not used after the beginning of the third trimester. Another common medication is Terbutaline (Brethine©), it can be given as an isolated intramuscular shot or as a pill. Side effects include feeling a little jittery and an accelerated pulse.