A 25-year-old woman, gravida 2 para 1, at 33 weeks gestation comes to the emergency department due to intermittent contractions that began after intercourse. The contractions initially occurred every 10-15 minutes and lasted 1 or 2 minutes. The patient drank some water and tried to rest, but the contractions continued. She has no vaginal bleeding or leakage of fluid. Fetal movement is normal. At 12 weeks gestation, the patient had a urinary tract infection caused by group B Streptococcus that was treated with antibiotics. Prenatal care has otherwise been uncomplicated. The patient's prior pregnancy ended with a term vaginal delivery. Temperature is 36.7 C (98.1 F) and blood pressure is 100/70 mm Hg. Fetal heart rate tracing has a baseline of 150/min, moderate variability, and multiple accelerations. Tocodynamometry shows contractions every 5-8 minutes. On speculum examination, the cervix is visibly 3 cm dilated and there is no evidence of rupture of membranes. Which of the following is the best next step in management of this patient?
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This patient at 33 weeks gestation has regular, painful contractions resulting in cervical dilation, findings consistent with preterm labor (ie, labor at <37 weeks gestation). Risk factors include prior spontaneous preterm delivery, short interpregnancy interval (eg, <6-18 months), and genitourinary tract infection (eg, group B Streptococcus [GBS], Chlamydia trachomatis).
Preterm labor management depends on gestational age. In patients at <34 weeks gestation, management includes attempts to delay delivery and minimize neonatal morbidity and mortality associated with preterm delivery. These interventions include:
Antenatal corticosteroids (eg, intramuscular betamethasone) to decrease the risk of neonatal respiratory distress syndrome. Corticosteroids promote fetal pneumocyte development and induce fetal surfactant production (ie, fetal lung maturity). In addition, they decrease the risk of intraventricular hemorrhage, necrotizing enterocolitis, and overall neonatal morbidity and mortality.
Penicillin to prevent vertical transmission of GBS, which occurs more frequently at preterm gestations.
Nifedipine tocolysis (administered between 32 and 34 weeks gestation) to temporarily halt preterm contractions and delay delivery.
In contrast, patients in preterm labor at 34-37 weeks gestation typically receive penicillin and expectant management only because the maternal risks (ie, adverse effects of tocolytic medications) outweigh the neonatal benefits. In addition, antenatal corticosteroids may be given, but its use at these gestational ages is not universal.
(Choice A) Bed rest and pelvic rest do not decrease rates of preterm delivery. Instead, bed rest increases maternal risk for deep venous thrombosis and bone density loss and is not recommended.
(Choice B) A cerclage placed in the second trimester can prevent preterm delivery in patients with cervical insufficiency (ie, prior painless, second-trimester losses). However, uterine contractions and gestational age >24 weeks are absolute contraindications for this procedure due to the increased risk of cervical injury.
(Choice D) Antenatal magnesium sulfate infusion decreases the risk of cerebral palsy in very preterm neonates. However, because of unclear neonatal benefits at ≥32 weeks gestation and potential maternal risks (eg, respiratory depression, cardiac arrest) associated with magnesium toxicity, it is not typically administered for fetal neuroprotection after 32 weeks gestation.
(Choice E) Patients with group B Streptococcus bacteriuria diagnosed during pregnancy, such as this patient, are considered persistently colonized and do not need rectovaginal culture. These patients require penicillin prophylaxis during labor.
Educational objective:
Intramuscular betamethasone, a corticosteroid, is indicated for patients at risk for preterm delivery at <34 weeks gestation. Betamethasone stimulates fetal lung maturity and decreases the risk of neonatal respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, and overall morbidity and mortality associated with prematurity.