How should the hypertensive pregnant patient be evaluated and treated?

First ask, what is the gestational age?

• if less than 20 weeks and blood pressure greater than 150/100, start antihypertensive medication in consultation with obstetrics.   Mild hypertension should not be treated as it does not decrease adverse events. 
• if greater than or equal to 20 weeks and blood pressure greater than 140/90, test urinalysis.  If greater than 1+ protein in UA, patient has preeclampsia or associated complication (ecalmpsia, HELLP syndrome); check CBC, basic chemistries, LFTs, uric acid, d-dimer, fibrinogen, coags and consult OB.  

Source 

Deak, T. and Moskovitz, J.  "Hypertension and Pregnancy"  Emerg Med Clin N Am.  Nov 2012.