Definition
A.Preterm labor (PTL) is defined as regular uterine contractions that produce documented cervical changes after 20 weeks and prior to 37 completed weeks of gestation. Cervical changes may include dilation, effacement, softening, or movement of the cervix to a more anterior position.
Incidence
A.PTL occurs in approximately 10% of the live births in the United States and precedes 50% of the preterm births (PTBs). It also accounts for more than 70% of neonatal mortality.
Pathogenesis
A.Infection, inflammation, decidual hemorrhage, and ischemia are common causes of PTL. Infection may originate from several sites, including the bladder, kidney(s), cervix, uterus, gastrointestinal tract, and upper respiratory tract. Ischemia may be caused by decreased oxygen delivery to the uterus because of maternal hypoxia, hypovolemia, or vena caval compression. Pathologic overdistension of the uterus in the presence of polyhydramnios or multiple gestation may cause PTL symptoms. Vaginal bleeding from a decidual hemorrhage (placental abruption) is associated with a high risk of PTL. The bleeding originates in damaged decidual blood vessels and presents clinically as vaginal bleeding or a retroplacental hematoma formation. However, in most cases, the cause is unknown.
B.Paternal risk factors: No paternal risk factors for the development of PTB in their partners have been identified. PTB risk is not increased by the father’s history of preterm children with other women or PTBs to members of the father’s family.
Prevention
A.Progesterone supplementation decreases the risk of PTB by approximately 30% in women with a singleton pregnancy and a history of a spontaneous single preterm delivery.
B.Women with a singleton pregnancy and a previous history of spontaneous PTB should be offered hydroxyprogesterone caproate 250 mg given via intramuscular (IM) route once weekly, starting at 16 to 24 weeks’ gestation, and continuing through 36 6/7 weeks’ gestation to reduce the risk of recurrent spontaneous PTB.
C.In asymptomatic women with a singleton gestation without a prior PTB with an incidentally identified very short cervix (<20 mm) before or at 24 weeks’ gestation, vaginal progesterone is recommended as a management option to reduce the risk of PTB. Vaginal micronized progesterone, 200 mg daily, is associated with a 44% decrease in spontaneous PTB at less than 34 weeks’ gestation and vaginal progesterone gel, 90 mg daily, has shown a 45% decrease in spontaneous PTB at less than 33 weeks’ gestation in asymptomatic women with a very short cervix.
Predisposing Factors
A.Previous PTL or preterm delivery is the major risk factor for recurrence.
B.Preterm premature rupture of membranes (PPROM).
C.Uterine anomalies, surgery, and fibroids.
D.Multiple gestations.
E.History of second-trimester abortion(s).
F.Incompetent cervix.
G.History of cervical surgery (cone biopsy or loop electrosurgical excision procedure [LEEP] for the treatment of cervical dysplasia).
H.Recurrent urinary tract and kidney infections, asymptomatic bacteriuria.
I.Polyhydramnios.
J.Fetal macrosomia.
K.Maternal age extremes (<18 or >40 years old).
L.Placenta previa.
M.Abruptio placentae.
N.Poor nutritional status and low prepregnancy weight.
O.Maternal dehydration.
P.Maternal race (occurs more frequently in African American population).
Q.Low socioeconomic status.
R.Inadequate prenatal care.
S.Anemia (Hgb <10 g/dL).
T.Substance use/abuse (smoking, drug, alcohol).
U.Vaginal infection.
V.Presence of fetal fibronectin, a protein produced by the trophoblast and other fetal tissues, has been noted in cervicalvaginal secretions between 24 and 34 weeks’ gestation in a subgroup of women who are at increased risk for PTB.
W.Short cervical length.
X.Short interpregnancy interval.
Y.Abdominal surgery during pregnancy.
Z.Episodes of vaginal bleeding in more than one trimester.
AA.Maternal first-degree family history of PTB, especially if the woman herself was born preterm.
AB.Fetal anomaly or fetal growth restriction.
AC.Intrauterine fetal demise.
Common Complaints
A.Abdominal pain or menstrual-like cramping.
B.Low backache.
C.Increase or change in vaginal discharge, gush
of fluid, loss of mucus plug, and bloody show or vaginal spotting.
D.Diarrhea.
E.Something’s not right.
Other Signs and Symptoms
A.Pelvic pressure (vaginal and/or rectal).
B.Contractions or period-like cramps.
Subjective Data
A.Review the patient’s past medical history and obstetric history, including risk factors for PTL.
B.Elicit information about the onset, frequency, duration, and course of abdominal pain or cramping; presence or absence of backache; the duration and frequency of these symptoms; and whether symptoms began subsequent to a certain event or activity. What, if anything, makes these symptoms better or worse?
C.Question the patient about color, odor, consistency, and amount of vaginal discharge or bleeding. Is the discharge clear, pink, blood-tinged, or bright red vaginal bleeding? Was there a spot the size of a quarter or a half-dollar? Has she been wearing a perineal pad? How often does she have to change the pad? Is the pad soaked with blood when she changes it?
D.For fetuses older than 18 weeks’ gestation, question the patient about frequency of fetal movements.
E.Question the patient about urinary frequency, presence of urgency, or dysuria. Is the urine discolored, blood-tinged, or malodorous?
F.Question the patient about recent sexual activity (i.e., has there been recent intercourse?).
G.If the patient complains of diarrhea, ask her if she has a fever and if anyone else in the family is ill.
Physical Examination
A.Check temperature, blood pressure (BP), pulse, respiratory rate, and fetal heart tones.
B.Inspect: Note general appearance of discomfort.
C.Palpate:
1.Abdomen: Note presence, frequency, and intensity of uterine contractions; resting tone; and the presence of uterine tenderness or suprapubic pain.
2.Measure fundal height and gently assess fetal lie, position, and estimated fetal weight via Leopold’s maneuvers (typically reliable after 24 weeks’ gestation). It may be difficult to palpate fetal parts in the presence of maternal obesity or polyhydramnios.
3.Back: Check for costovertebral angle (CVA) tenderness.
D.Auscultate: Auscultate the heart and lungs (especially if the patient is on tocolytics).
E.Pelvic exam:
1.Sterile speculum exam: Visualize the cervix for an estimate of dilation. Evaluate rupture of membranes and vaginal discharge or bleeding. If meconium-stained amniotic fluid is noted, immediately consult a physician and transfer the patient to a hospital. Note if meconium is thin or thick (thick meconium may be associated with breech presentation).
2.Bimanual exam: After rupture of membranes and placenta previa have been excluded by the patient history, sterile speculum exam, physical exam, laboratory testing, and ultrasound (US) evaluation, as appropriate, perform a gentle bimanual examination. Note cervical dilation, effacement, station, cervical position, and softness of cervix.
3.Cervical exam during pregnancy: See Section II: Procedure Bimanual Examination: Cervical Evaluation During Pregnancy.
Do not perform a digital examination of the cervix if premature rupture of membranes (PROM) is present without active labor or before a US has been performed to confirm placental location.
Diagnostic Tests
A.White blood cell (WBC), if indicated.
B.Urine dipstick for ketones, leukocyte, esterase, protein, and nitrite.
C.Evaluate vaginal discharge for pH with phenaphthazine (nitrazine) tape.
Note: False-positive and false-negative nitrazine test results occur in approximately 5% of cases.
False-negative test results can occur when leaking of amniotic fluid is intermittent or is diluted by other vaginal fluids. False-positive results can be caused by alkaline fluids in the vagina such as blood, seminal fluid, or soap.
D.Check ferning, if discharge is nitrazine positive or PPROM is suspected. When viewed under a microscope, amniotic fluid produces a delicate ferning pattern in contrast to the thick, wide branching pattern seen with cervical mucus.
Note: A false-positive fern test can be caused by well-estrogenized cervical mucus or a fingerprint on the microscope slide. A false-negative result can be caused by inadequate amniotic fluid collection on the vaginal swab or if the sample collected is heavily contaminated by other vaginal fluids or blood.
E.Wet prep, if indicated.
F.Cervical cultures for sexually transmitted infections (STIs; gonorrhea and chlamydia).
G.Cervical and rectal culture for group B strep (GBS; if not performed in the previous 5 weeks).
H.Fetal fibronectin, where available. Candidates for fetal fibronectin testing must meet the following criteria:
1.Intact fetal membranes.
2.Cervical dilatation less than 3 cm.
3.Gestational age 24 0/7 weeks to 34 6/7 weeks.
4.No sexual intercourse in preceding 24 hours.
5.No gross vaginal bleeding.
A positive fetal fibronectin result correlates with an increased risk of preterm delivery with in 7 days.
Note: False-positive results can occur because of ejaculate from coitus within the previous 24 hours, a grossly bloody specimen, or a digital cervical exam. A digital cervical exam can also produce a false-negative result. Administration of intravaginal substances, such as lubricants, medications, or douching, may also interfere with the assay.
Urine culture: Asymptomatic bacteriuria is associated with an increased risk of PTL.
I.Urine drug screen: In patients with risk factors for substance abuse, because of the link between cocaine use and placental abruption.
J.Ultrasonography: Fetal biometry and dating, cervical length, amniotic fluid volume, biophysical profile (BPP), placental location, fetal presentation, ruling out fetal, placental, and maternal anatomic anomalies.
K.Electronic fetal monitoring (EFM) for contractions and fetal heart rate (FHR).
Differential Diagnoses
A.PTL.
B.Preterm (or Braxton Hicks) contractions, with no cervical change.
C.Incompetent cervix.
D.PPROM.
E.Low back muscle strain.
F.Pyelonephritis or urinary tract infection (UTI).
G.Placenta previa.
H.Abruptio placentae.
I.Gastroenteritis.
J.Vaginal infection.
K.Maternal dehydration.
L.Ketoacidosis.
M.Round ligament pain.
Plan
A.General interventions:
1.Regular uterine contractions with cervical dilation or effacement, with pressure on the lower uterine segment, strongly indicates PTL.
2.If the cervix is dilated more than 3 cm with contractions upon presentation, the patient is probably having PTL. Consult with a physician for hospital admission and tocolytic candidacy.
3.If the patient is symptomatic with a positive fetal fibronectin test, consult with a physician for maternal transfer to a hospital equipped to care for preterm infants.
4.Second trimester: If the patient shows signs and symptoms of PTL, consider diagnosis of incompetent cervix. Refer the patient to a physician for ultrasonography for cervical length and possible cerclage placement.
B.Outpatient management:
1. 
See Section III: Patient Teaching Guide Preeclampsia (PIH).
2.Outpatient bedrest is not beneficial. While bedrest improves uteroplacental blood flow and can lead to a slight increase in fetal birthweight, there is no evidence that it decreases the incidence of PTB. Additionally, prolonged immobility increases the risk of thrombolytic events, has clear negative psychosocial effects on patients and families, and leads to musculoskeletal deconditioning.
3.Limit physical activity: Women at high risk for PTL should reduce their level of physical activity/exercise, particularly strength training, and occupational activities that require heavy lifting.
4.Prophylactic treatment against infection is not recommended. There is no clear evidence of benefit from prophylactic antibiotic therapy in women with PTL with intact membranes and no evidence of infection.
5.Sexual activity: Patients should consider avoiding sexual activity if they experience an increased frequency or intensity of contractions after sexual intercourse.
6.Administer corticosteroids to enhance fetal lung maturity if less than 34 weeks’ gestation. Observe the patient for contractions in the office.