The goal of this study is to learn how a pregnant person's body processes caffeine and how much caffeine crosses the placenta to the baby. A small dose of caffeine will be given to each pregnant participant before delivery. Blood will be drawn to measure caffeine levels in the pregnant mother. Blood will also be taken from the placenta and from the newborn to measure caffeine levels. This data will be used to form a computer model of the metabolism of caffeine during pregnancy.

Inclusion Criteria:

1. Pregnant women with risk of preterm delivery at 23 - 31+6 weeks with singleton gestation who are inpatient without a plan for discharge before delivery.
2. Informed consent provided for participation.
3. Cesarean delivery.

Exclusion Criteria:

1. Known major fetal congenital anomalies or genetic disorders.
2. Plan in place for limited neonatal resuscitation or comfort care only.
3. Preterm, premature rupture of membranes prior to 22 weeks gestation with concern for pulmonary hypoplasia.
4. Pre-eclampsia, gestational hypertension, or other gestational hypertensive disorder.
5. Fetal arrhythmia.
6. Seizure disorder.
7. Oligohydramnios due to renal anomalies or renal impairment.
8. Current or anticipated use of products that include sodium benzoate.
9. Maternal age <18 years.
10. Maternal medical conditions in which caffeine or other stimulants would be contraindicated.
11. High likelihood of receiving terbutaline.
12. Use of the following medications, which may affect caffeine metabolism: fluvoxamine, ciprofloxacin, methoxsalen, mexiletine, vemurafenib, phenytoin, rifampin, and teriflunomide.
13. Significant acute or chronic medical, neurologic, or illness in the patient that, in the judgment of the Principal Investigator, could compromise subject safety, limit the ability to complete the study, and/or compromise the objectives of the study.