Inclusion Criteria:
* Pregnant women
* Gestational age: 23 weeks, 0 days to 35 weeks, 6 days
* Hypertensive disorder of pregnancy including gestational hypertension or preeclampsia, the non-severe form at enrollment, which is called without severe features by the American College of Obstetricians and Gynecologists.
* No evidence of the severe form of preeclampsia, termed severe features, as outlined in maternal exclusions
* No indication for delivery at the time of enrollment.
* Planned expectant management at time of enrollment
* Singleton or dichorionic twin gestation, defined at and beyond 14 weeks gestation. (A pregnancy complicated by a vanishing twin in the first trimester defined as less than 14 weeks gestation will be eligible.)
* Intact membranes
Exclusion Criteria:
* Preeclampsia with severe features, defined per ACOG as:
* Systolic blood pressure of 160 mm Hg or more, or diastolic blood pressure of 110 mm Hg or more on two occasions at least 4 hours apart (unless antihypertensive therapy is initiated before this time)
* Thrombocytopenia defined as: lower than 100 x 10e9 platelets/L
* Impaired liver function that is not accounted for by alternative diagnoses and as indicated by abnormally elevated blood concentrations of liver enzymes (to more than twice the upper limit normal concentrations), or by severe persistent right upper quadrant or epigastric pain unresponsive to medications
* Renal insufficiency (serum creatinine concentration more than 1.1 mg/dL or a doubling of the serum creatinine concentration in the absence of other renal disease)
* Pulmonary edema
* New-onset headache unresponsive to medication and not accounted for by alternative diagnoses
* Visual disturbances
* Underlying renal dysfunction defined as, presenting the following parameters prior to 20 weeks gestation: baseline creatinine, equal to or higher than, 1.2 mg/dL Or proteinuria: defined as presenting protein in urine, equal to or higher than, 300 mg/24 hours or protein/creatinine ratio, equal to or higher than, 0.3 or Urine dipstick reading of greater than or equal to 2 at baseline and in the absence of a urinary tract infection
* Stage 2 chronic hypertension
* Contraindications to labetalol and nifedipine XL according to the FDA package insert
* Patient unable to or unwilling to adhere to management recommendations
* Fetal Reasons for Study Ineligibility:
* Fetal growth restriction (lower than 10th percentile) at enrollment, based on an ultrasound within 3 weeks prior to enrollment
* Oligohydramnios defined by amniotic fluid deepest vertical pocket \<2 cm based on an ultrasound within the 48 hours prior to enrollment
* Known major structural or chromosomal abnormality
