What is the diagnosis for a 30-year-old woman, gravida (number of times pregnant) 3, para (number of viable births) 2, at 37 weeks gestation, presenting with regular, painful contractions, a cervix 4 cm dilated and 90% effaced, and a taut, bulging bag with no presenting fetal part, but normal fetal movement and a normal fetal heart rate tracing with moderate variability and multiple accelerations?

Differential Diagnosis

• Single most likely diagnosis
  • Obstructed Labor due to Occiput Posterior Position or other Malposition: The presence of a taut, bulging bag with no presenting fetal part and the patient being 4 cm dilated and 90% effaced at 37 weeks gestation suggests that the labor might be obstructed due to a malposition of the fetus, such as occiput posterior position. This is a common cause of labor obstruction and the symptoms presented are consistent with this diagnosis.
• Other Likely diagnoses
  • Prolonged Latent Phase of Labor: The patient has been in labor for only an hour, and it's possible that she is still in the latent phase, which can be prolonged. However, the presence of a bulging bag suggests that there might be an obstruction.
  • Cephalopelvic Disproportion (CPD): Although less likely given the patient's parity and previous vaginal deliveries, CPD could be a cause of obstructed labor. The fact that the patient has had previous successful vaginal deliveries makes this less likely.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Uterine Rupture: Although the patient's abdomen is nontender between contractions, uterine rupture is a life-threatening emergency that must be considered, especially in a patient with a history of previous uterine surgery or scars. The presence of a taut, bulging bag could also be indicative of uterine rupture.
  • Placental Abruption: The absence of vaginal bleeding does not rule out placental abruption, and this condition can cause obstructed labor. The patient's presentation and the fetal heart rate tracing do not strongly suggest abruption, but it must be considered.
• Rare diagnoses
  • Umbilical Cord Prolapse: The presence of a bulging bag could be indicative of umbilical cord prolapse, although this is less likely given the absence of a presenting fetal part and the fact that the patient has not reported any leakage of fluid.
  • Amniotic Fluid Embolism: Although extremely rare, amniotic fluid embolism is a life-threatening condition that can occur during labor. The patient's presentation does not strongly suggest this diagnosis, but it must be considered in the differential diagnosis.