Preterm Labor

Definition/Etiology:

False labor is contractions that do not result in cervical change.

True labor:

• Contractions >8/hour PLUS
• Cervical dilation >3 cm OR
• Cervical length <2 cm on transvaginal ultrasound OR
• Cervical length 2-3 cm and positive fetal fibronectin (swab collection from cervix)

Gestational age >34 weeks: just let them deliver

Gestational age 20-34 weeks:

• Steroids IV given to mom to protect neonate against mortality
• Tocolytics for up to 48 hours to delay birth (Indomethacin, Nifedipine)
• Antibiotics for prophylaxis against early-onset neonatal group B streptococcal (GBS) infection
• Magnesium sulfate IV for fetal neuroprotection if <32 wks

Gestational age 20-22 weeks is considered the earliest possible time for tocolysis, and is generally only attempted if there is an acute issue like appendicitis or pyelonephritis causing preterm labor which is curable and unlikely to cause recurrent preterm labor.

Pathophysiology:

Preterm labor is usually precipitated by:

• Pathological uterine distention
• Placental abruption
• Exaggerated inflammatory response to altered genital tract microbiome / infection
• Stress-induced premature activation of the maternal or fetal hypothalamic-pituitary-adrenal axis, leading to hormonal changes

Can also be precipitated by:

• Acute abdomen (appendicitis, bowel obstruction, cholecystitis)
• Pyelonephritis
• Placental abruption
• Pneumonia
• Thyroid storm
• Premature rupture of membranes

Clinical Presentation:

• Menstrual-like cramping
• Mild, irregular contractions
• Low back ache
• Pressure in vagina and pelvis
• Vaginal discharge of mucus, clear, or slightly bloody
• Spotting, light bleeding

True labor is accompanied by cervical changes over hours:

• Dilation (>3cm supports actual preterm labor)
• Effacement (thinning and shortening)
• Softening
• Anterior position

Collaborative Management:

Transvaginal ultrasound:

• Can determine if cervix is insufficient and membranes are prolapsing
• Cervix length <3cm increases suspicion of preterm labor

Obstetric ultrasound:

• Cervical length
• Fetal position
• Placental abnormalities
• Fetal abnormalities
• Fetal weight

Labs:

• Urine culture
• Rectovaginal group B streptococcal (GBS) culture
• Gonorrhea, chlamydia, syphilis testing PRN

Evaluation | Patient Monitoring | Education:

• Fetal heart rate monitoring
• Frequent maternal vitals
• May need to transfer to a facility with a NICU
• Monitor timing of contractions

Linchpins: (Key Points)

• Gestational age 22-34 weeks is considered the timeline in which interventions can promote maternal/fetal safety and provide benefit.
• Coordinate transfer to a facility with a NICU if indicated.
• Collaborate with labor & delivery colleagues.
• Monitor vitals for bleeding and placental abruption.