It is well established that preeclampsia with severe features warrants delivery at or beyond 34 weeks, but the various triggers for delivery before 34 weeks can be a source of confusion. Here is a quick reference summarizing the recommendations in figure 5-2 of the ACOG 2013 Hypertension in Pregnancy document.
Every patient with a viable pregnancy and preeclampsia with severe features should be admitted or transported to an adequately equipped hospital and observed in labor and delivery for 24 to 48 hours. Magnesium sulfate should be administered along with antenatal corticosteroids if appropriate. Antihypertensive medications should be used to treat severe hypertension. Ultrasound for fetal weight, fluid, and position should be performed. Fetal and maternal status should be reevaluated on at least a daily basis with NSTs, vital signs, and symptom review along with periodic laboratory evaluation. Each result should prompt evaluation of whether continued expectant management is justified. If the patient is stable she should remain inpatient until delivery, and magnesium sulfate should be stopped after 24 hours. Oral antihypertensives should be initiated if BP is consistently greater than 150/100. Every pregnancy between the age of viability and 33 weeks 6 days should be managed expectantly unless one of the conditions below is met.