Preterm Labor Diagnosis

Preterm labor happens when a woman’s body prepares for birth before the baby is considered full term, which is 37 weeks into the pregnancy. Doctors monitor for signs that labor may be taking place before the baby’s due date. These physical changes can include “dropping,” or “lightening,” when the unborn baby begins to move toward the birth canal, and contractions, when the uterus contracts and relaxes in preparation for birth. 

If you are entering labor, you may notice symptoms such as a heavy feeling in the pelvis, cramping, spotting or bleeding, backache, and intermittent pelvic pain that lasts 30 to 90 seconds. You may also experience painful uterine contractions, which feel like a tightening and relaxing of the abdomen, that occur every 10 minutes or more often during an hour. You may “break your water,” which means the fluid-filled amniotic sac surrounding the baby ruptures and liquid trickles or gushes from your vagina. Some women have no obvious symptoms before labor begins.

Contact your doctor if you have symptoms of labor while pregnant; you may be advised to go to the doctor’s office or to the hospital. From there, your doctor can determine whether you are in labor. Depending on your overall health and the week of the pregnancy, your doctor may recommend going ahead with the birth or taking steps to delay it.

The symptoms of preterm labor don’t always mean a baby is delivered prematurely. Though one in eight babies is born prematurely in the United States each year, according to the U.S. Centers for Disease Control and Prevention, up to half of women diagnosed with preterm labor deliver full-term babies. More than 70 percent of premature babies are “late preterm” babies, born between weeks 34 and 37 of pregnancy. Frequently, they fare nearly as well outside the womb as full-term babies.

If you are showing signs of labor, your doctor may decide to watch and wait or allow labor to progress naturally if you are 34 to 37 weeks pregnant, your water hasn’t broken, and the baby isn’t showing signs of distress, such as a rapid heartbeat.

Confirming the Onset of Preterm Labor

To confirm that preterm labor is taking place, your doctor conducts a pelvic exam to determine whether your cervix has begun to dilate, or open, to prepare for birth. Your doctor may also use transvaginal ultrasound to determine if the cervix has effaced, or thinned, to prepare for dilation.

NYU Langone specialists use several other techniques and tests to confirm preterm labor, including the following.

Monitor Contractions

If you are having contractions, your doctor uses a tocodynamometer, which is attached to a band and held in place against your belly, to monitor and measure uterine contractions. This helps your doctor to determine the regularity and frequency of the contractions, which may indicate labor.

Fetal Fibronectin Screening

If you are experiencing regular contractions before 34 of pregnancy, your doctor may swab the cervix and test the secretions for fetal fibronectin. This is a protein that helps the amniotic sac, the membrane that cushions the baby during pregnancy, stay attached to the lining of the uterus. Because the protein begins to break down as the body prepares for birth, detecting the presence of fetal fibronectin in vaginal discharge in the second and third trimesters of pregnancy can signal a high risk of labor.

Usually, a lack of fetal fibronectin in the vagina means that labor is not likely to begin for the following two weeks. To avoid a false-positive result, it’s important that nothing has been placed in your vagina for 24 hours prior to the test.

Urine Test

If you’re experiencing the symptoms of labor before week 37 of pregnancy, your doctor may ask for a urine sample in order to check for a bladder or urinary tract infection, which can lead to preterm contractions. When these infections are successfully treated, preterm contractions often stop. Typically, it takes two to three days for the antibiotics to begin managing the infection.