Preterm Labor Williams CH.36

Preterm Birth Death, severe neonatal morbidities Common before 26 weeks Universal before 24 weeks

Worse Outcomes Chronic lung disease Grade 3 and 4 intraventricular hemorrhage Periventricular leukomalacia

Threshold for neonatal mortality: 1600g Threshold for neonatal morbidity: 1900g

Cause of Preterm Birth Medical and obstetrical complications Preeclampsia, fetal distress, IUGR, placenta abruption History of threatened abortion Lifestyle factors Smoking, inadequate weight gain, drug abuse, age, short stature, occupation, poverty Genetic factors Chorioamnionitis

Prior Preterm Birth

Incompetent Cervix Mean cervical length at 24 weeks: 35 mm Cervical Dilation 2~4 mm during 2nd trimester: predict birth prior to 35 weeks

Infections Bacterial vaginosis Tricomonas (low birth weight, preterm birth, perinatal death) Periodontal disease

Premature Membrane Rupture PPROM

Incidence during 24~34 weeks 1.7 % of pregnancy 20 % of all prenatal deaths 7 % delivery delayed > 48 hours Better outcome Volume of amniotic fluid after PPROM Prognositc importance before 26 weeks PPROM < 23 weeks: lung hypoplasia

Antimicrobial therapy Prolong latency period after PPROM If chorioamnionitis is diagnosed Fever Vaginal delivery

If PPROM beyond 34 weeks Oxytocin to induction of labor C/S if indicated

Preterm Labor

Signs and symptoms Painful or painless uterine contractions Pelvic pressure Menstrual-like cramps Watery vaginal discharge Low back pain

Diagnostic critiria Uterine contraction 4 in 20 mins 8 in 60 mins with cervical change Cervical dilatation > 1 cm Cervical effacement > 80%

Glucocorticoid Betamethasone 12mg IM stat and 24 hours later Effective: 24 hours after initial dose Effect up to 7 days Adverse effect: Pulmonary edema Infection Difficult glucose control in DM women

Bed rest (+) Hydration (-) Antimicrobials (-, if no PPROM) Emergency cerclage (+)

Drug to Inhibit Preterm Labor

Beta-Adrenergic Agonist Ritodrine Beta-adrenergic receptor desensitization Side effect: Pulmonary edema Hyperglycemia Arrhythmia

Magnesium Sulfate Calcium antagonist Cleared almost by renal excretion 4 g loading dose  2 g/hr continuous dose Therapeutic range: 4~7 mEq/L 1 mEq/L = 1.2 mg/dl = 0.5 mmol/L Deep tendon reflex disappear 10 mEq/L Respiratory arrest 12 mEq/L

Prostaglandin Inhibitors Indomethacin Total 24 hours dose < 200 mg Side effect: Oligohydramnios (reversible)

Calcium Channel Blockers Nifedipine (adalat) Side effect: Hypotension Decrease uteroplacental perfusion

Atosiban Nonapeptide oxytocin analogue Competitive antagonist of oxytocin- induced contractions Side effect: Nausea, vomiting, headache, dizziness, money loss NTD/day

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