The investigators propose a randomized controlled unblinded trial to evaluate rates of optimal blood pressure control between Nifedipine 60mg XL once daily vs. Nifedipine 30mg XL twice daily in patients admitted for expectant management with pre-eclampsia with severe features. Patients will be approached for consent when they are placed on 30mg of Nifedipine daily by their primary provider and will be enrolled in the study when the primary provider has made the decision to increase the patient's daily dose of Nifedipine XL from 30mg to 60mg.

This is a randomized controlled unblinded trial at The Ohio State University comparing Nifedipine XL 60mg daily to 30mg twice daily in patients admitted for expectant management for pre-eclampsia with severe features.

Potential study participants will be identified at the time of admission to the antepartum unit. Inclusion criteria must be met, namely patient's age, gestational age, diagnosis of preeclampsia with severe features.

Patients will be approached for consent when they are placed on 30mg of Nifedipine daily by their primary provider and will be enrolled in the study when the primary provider has made the decision to increase the patient's daily dose of Nifedipine XL from 30mg to 60mg. Participants will be randomized in to one of two groups:

• Once daily Nifedipine XL 60mg Vs.
• Twice daily Nifedipine XL 30mg

Once enrolled and randomized, blood pressures will be monitored every 4 hours as is standard on the antepartum unit. Blood pressures for the primary outcome will be collected 24 hours after the patient is randomized and initiated on their above regimen. This is to allow the medication to reach steady state prior to collected information on optimal blood pressures. The primary outcome will consist of blood pressure values collected q4 hours beginning 24h-48h after receiving their first dose of the randomized dose regimen.

Algorithms for the administration of intravenous labetalol, Nifedipine or hydralazine will be utilized by the primary provider at his or her discretion.

Women may take the medication concurrently with intravenous labetalol, hydralazine, or immediate release Nifedipine for the treatment of severe blood pressures as determined by their primary provider.

All other obstetric care will be at the discretion of the primary provider, including but not limited to addition of second long-acting hypertensive agents, decision to proceed with delivery, IV magnesium for seizure prophylaxis and recommendations regarding mode of delivery. Data will be collected on these components of routine obstetric care. Analysis will be by intent to treat.

A subset of patients will be enrolled for a pharmacokinetic study and blood will be collected at prespecified times following administration of the randomized Nifedipine XL regimen.

Inclusion Criteria:

• Women age 18-45 with a viable single or twin intrauterine pregnancy between 22 0/7 and 33 6/7 weeks gestation based on the best obstetric estimate by ACOG criteria.
• Undergoing expectant management for a diagnosis of preeclampsia with severe features and already initiated on 30mg Nifedipine XL. The patient may or may not have already received acute treatment for severe blood pressures.

Exclusion Criteria:

• Known allergy or adverse reaction to Nifedipine or any medical condition where Nifedipine is contraindicated, such as galactose intolerance, severe GI stricture, and GI hypomotility disorder.
• Participation in another trial without prior approval
• Currently receiving a daily dose of Nifedipine XL of 60mg or greater
• Continuation of alternate long-acting anti-hypertensive medication on admission
• Physician/provider or patient refusal
• Triplet or higher order pregnancy

Pregnant women undergoing expectant management for a diagnosis of preeclampsia with severe features already initiated on 30mg Nifedipine XL and the primary provider has made the decision to increase the patient's daily dose of Procardia XL from 30mg to 60mg. .