Preterm Labor
Rationale
The reduction of preterm births remains an important goal in obstetric care.
Understanding the causes and recognizing the symptoms of preterm labor provides the basis for management decisions.
Preterm Labor
Definition
Labor prior to 37 weeks gestation (259 days)
Labor: presence of uterine contractions between 20-37 weeks gestation leading to cervical change
Dilation
Effacement
Station
Complicates 8-10% pregnancies
Preterm Birth
Any delivery occurring prior to 37 weeks
Incidence – 11% of live-births
1/3 of PTB due to spontaneous rupture of membranes
1/3 of PTB due to obstetrical causes
1/3 of PTB due to idiopathic preterm labor
Preterm Labor
Consequences
Severity and frequency increase as gestational age decreases
75% of perinatal deaths are associated with sequellae of preterm birth, including:
RDS
IVH
NEC
Sepsis
Neurologic deficits / seizures
Preterm Labor
Leads to preterm birth 40-50%
Most common cause of perinatal morbidity and mortality
In U.S., 8-10% of babies born prematurely account for 60-75% of all perinatal morbidity and mortality
Preterm birth accounts for 35% of all U.S. health care
spending for infants
Preterm Labor Potential causes
Idiopathic – most common
Dehydration
PROM – can be secondary to subclinical infection of fetal membranes
Infection
Cervical
Intraamniotic
Urinary
Preterm Labor
Potential causes
Excessive uterine enlargement
Polyhydramnios
Multiple gestation (1% pregnancies)
Uterine distortion
Leiomyomas
Müllerian anomalies
Placental anomalies
Previa
Abruption
Preterm Labor
Potential causes
Incompetent cervix
Substance abuse
Fetal anomalies
Iatrogenic
Induction of labor because of maternal or fetal health complication (such as severe preeclampsia)
Risk Factors
History of preterm labor and delivery If one early delivery, risk with next pregnancy: 2x
If two early deliveries, risk with next pregnancy: 3x
Smoking
Non-white
Low socioeconomic status
Uterine malformation
Vaginal infections
Pre-pregnancy weight <50 kg
Preterm Labor
Symptoms Menstrual-like cramps
Low, dull backache
Pelvic pressure
Abdominal cramping
Uterine contractions
Cervical dilation without feeling contractions
Vaginal bleeding
Preterm Labor
Evaluation EFM to monitor FHTs and frequency/duration
of contractions Strength of contraction cannot be assessed with
external monitors
Abdominal palpation by an experienced nurse can assess mild, moderate or severe contractions
Obtain cervical cultures Gonorrhea
Chlamydia
Group B Strep
Preterm Labor Evaluation
Assess cervical status
Dilation, effacement, station
Urine culture
Abdominal / Fundal exam to assess evidence of tenderness (infection)
Obtain fFN (if cervix hasn’t been digitally checked in 24 hrs and visually less than 3 cm dilated)
Sonogram if evidence of labor or other abnormality
Fetal Fibronectin
Fetal fibronectins are large molecular weight glycoproteins found in the plasma and extracellular matrix.
Identified in amniotic fluid, extracts of placental tissue, and malignant cell lines, and is recognized by the monoclonal antibody FDC-6.
Indicated for 22-34 weeks gestation.
Fetal Fibronectin
FFN is thought to be a "trophoblast glue" that promotes cellular adhesion at uterine-placental and decidual-fetal membrane interfaces. It is released into cervicovaginal secretions when the extracellular matrix of the chorionic/decidual interface is disrupted; this is the rationale for measurement of fFN as a predictor of PTD.
Preterm Contractions
Evidence of contractions, but not labor
IV/PO hydration
Benadryl 50mg IV/PO Q 6hr or
Terbutaline 0.25mg SQ Q 30 min
Prolonged observation
Reassurance
Preterm Labor
Evidence of Labor At what gestational age can the pediatrician
comfortably accept the neonate If < acceptable gestational age and pt remote from
delivery, tocolyze and arrange immediate transport
Start GBS prophylaxis
steroids Betamethasone or Dexamethasone if < 34 wks
If < acceptable gestational age and pt very near delivery, try to have NICU team receive the neonate and then transport to NICU
Preterm Labor Evidence of Labor
Tocolytics have not been shown to prolong pregnancy beyond a few days
MgSO4
Competes with Ca++ for entry into smooth muscle
β-adrenergic agents
Activation of adenyl cyclase, increased cAMP, decreased myosin light chain kinase activity
Ritodrine
Terbutaline
Prostaglandin synthetase inhibitors
Indomethacin
Ca++ channel blockers
Nifedipine
Preterm Labor
Evidence of Labor
Contraindications to tocolysis
Gestational age > 35-36 wks
Severely anomalous fetus
Intrauterine infection
Significant vaginal bleeding
Other obstetric conditions such as non-reassuring fetal status
Preterm Labor
Evidence of Labor
When in doubt, stabilize patient and transfer to center with a NICU.
Patient may arrest with advanced cervical dilation and it may be advisable that the patient not be further than 15-20 minutes away from a NICU.