The study will extend recent discoveries that have been made in basic human physiology related to responses melatonin and uterine contractions in late- or full-term pregnant women. The basic physiology work has been conducted in in vitro models of the human myometrium characterizing its responses to melatonin, and in pilot in vivo studies correlating the number of uterine contractions with melatonin concentrations that were manipulated by different types of light exposure. The planned experiments will test a causal link between circulating melatonin levels and uterine contractions in full-term pregnant women by manipulating melatonin levels using exogenous melatonin (i) during the day when endogenous levels of melatonin are very low (Experiment 1), and (ii) during the evening under conditions with lighting that would be expected to suppress the higher evening and nighttime levels of endogenous melatonin (Experiment 2).

Inclusion Criteria:

• nulliparity, age between 18 and 35,
• BMI<36 pre-pregnancy,
• ≥38 weeks of pregnancy with a single fetus at time of study.

Exclusion Criteria:

• color blind;
• prescription drugs affecting sleep, melatonin, and/or circadian rhythms (e.g., beta blockers, non-steroidal anti-inflammatory drugs);
• a health or pregnancy related condition that might affect melatonin or uterine contractions;
• medical conditions or medications for which melatonin might be contraindicated or there may be a drug interactions (e.g., Central Nervous System depressants/sedatives, Fluvoxamin (Luvox), medications for diabetes, immunosuppressants, anti-coagulants, Nifedipine, Verapamil).

Note: We cannot list all possible exclusionary criteria. Dr. Carolina Bibbo (co-I), our Obstetrics Investigator at Brigham and Women's Hospital (BWH), will make final determination of suitability including any safety concerns for each potential participant.

Per the NIH Policy on Data Sharing, we will make the datasets available to other investigators following publication of the final study results. We will make data available on a public database, such as the NIH-supported National Sleep Research Resource (NSRR; sleepdata.org). Outside investigators should submit their request in writing to the PI. Additional details below in Access Criteria

Upon request and following publication of the final study results

Outside investigators should submit their request in writing to the PI. A data-sharing agreement will be required. The request must be in accordance with MGB Policies and Harvard Medical School (HMS) guidelines. Such datasets will not contain identifying information per the regulations outlined in HIPAA, and permission will be obtained from study participants to share their data with researchers outside MGB. Per standard MGB policies, we will require a data-sharing agreement from any investigator or entity requesting the data; this agreement will include: (i) a commitment to using the data only for research purposes and not to identify any individual participant; (ii) a commitment to securing the data using appropriate computer technology; and (iii) a commitment to destroying or returning the data after analyses are completed.