A Quick Review of AFP's "Preterm Labor"

Preterm Labor
WILLIAM G. SAYRES,JR., MD,Group Health Cooperative, Spokane, Washington
http://www.aafp.org/afp/2010/0215/p477.pdf
Am Fam Physician. 2010 Feb 15;81(4):477-484

     The common causes of preterm labor are spontaneous labor with intact membranes, preterm premature rupture of membranes, and iatrogenic (such as preterm induction). Infant mortality rates increase for those born before 32 weeks gestation.  Some of the risk factors for preterm delivery include a previous preterm birth, infection, tobacco, alcohol, cocaine or heroin use, a history of LEEP, multiple gestations, or periodontal disease. A shortened cervix (less than 3 cm) is a risk factor. Cervical effacement normally starts at 32 weeks gestation.
     Bacterial vaginosis is a risk factor for preterm labor.  Screening and treating with clindamycin will lower the rate of PPROM and low birth weight babies. Diagnosis can be done with a gram stain or by using the Amsel criteria (having at least three of the following;
amine color with KOH,
presence of clue cell,
ph above 4.5, and
a thin vaginal discharge.)
The USPSTF recommends against BV screening due to insufficient evidence. The CDC suggests treatment, with reevaluation one month later.
     Antenatal progesterone has shown benefit in maintaining uterine dormancy. It is recommended for mothers with a previous spontaneous birth before 37 weeks. The three antenatal interventions shown to be effective for women presenting with preterm contractions are;
corticosteroids,
antibiotic prophylaxis against GBS, and
transferring the patient to a NICU.
     The initial assessment of these patients includes gestational age, determining if the membranes are ruptured, determining if the patient is in labor, if there is an infection, and determining the likelihood of a preterm delivery. Assessing the membranes can be done with a fetal fibronectin test (looking for ferning) and a nitrazine test (looking for alkalinity).  The test can be confirmed with a transabdominal amnioinfusion of indigo carmine, or by seeing oligohydramnios on ultrasound.
     All pregnant patients are screened for bacteriuria and pyelonephritis with a urine culture. A rectovaginal culture can be used if the patient was not previously screened. Antibiotic prophylaxis (penicillin, ampicillin, cefazolin, clindamycin, or erythromycin) should be give to those who tested positive. Patients should also be screened for  gonorrhea, chlamydia, BV and trichomoniasis.
     It is important to determine if the patient is actually in labor. Contractions should occur every 6 minutes, the cervix should be dilated to 3 cm or more, and it should be at least 80% effaced. The membranes may have ruptured and there may be bleeding. If labor has begun between 24-34 weeks, corticosteroids (betamethasone or dexamethasone) should be given to help fetal lung maturity. Tocolysis is needed so that the steroids have time to work (48 hours). Examples of tocolytics include indomethacin, Magnesium sulfate, nifedipine, terbutaline, and calcium channel blockers.