Circadian rhythm is the body's internal clock that synchronizes the body's physiological functions according to the 24-hour sleep-wake cycle. An individual establishes a circadian rhythm 3 months after birth, which is a progressive phase that involves regulating hormones such as cortisol and melatonin. According to previous studies, the synchronization of circadian rhythm between mother-infant pairs have been found to be beneficial in the growth and development of the child by regulating a 24-hour sleep-wake cycle. However, circadian disruption may cause excessive maternal cortisol which can be transferred to the fetus through the placenta during pregnancy and cause growth retardation. Growth faltering during infancy is associated with increased risks of morbidity from infections and chronic diseases in later life. Therefore, it is important to study the relationship between maternal circadian rhythm with synchronization of infant circadian rhythm as it may be one of the potential factors which affects the growth and development of the child.

On the other hand, infant temperament is affected by the maternal and infant circadian rhythm and may also be a predictor to mood disorders such as depression and anxiety. A systematic review reported that high cortisol levels during third trimester of pregnancy is associated with higher emotional reactivity and more difficult temperament infants. Other than the biological factors determining infant temperament, maternal psychological wellbeing during and after pregnancy is also an important element. It has been found that elevated maternal stress was associated with negative infant temperament, resulting in decreased sleep quality of the infant. Negative infant temperament may be a predictor to disordered eating behaviors and growth development. As infant temperament is an important factor in determining growth and development, the risk factors to negative temperament should be studied.

This study aims to determine the role of prenatal and postnatal factors with the infant circadian rhythm and its relationship with infant growth and temperament at 6 months. This study also includes the validation of the Chrononutrition Profile Questionnaire (CPQ) among pregnant women. Through the validation of CPQ, future research about chrononutrition behaviors and eating misalignment can be conducted to replace food record. The design of this study is a prospective observational cohort study. Data will be collected during 3rd trimester of pregnancy, whereas follow-up data on birth outcomes will be collected at birth. At 3 months after birth, data on maternal and infant circadian rhythm will be assessed, then data on growth and development will be collected at 6 months after birth. Data collection is elicited through a properly designed and validated questionnaire namely Chrononutrition Profile Questionnaire (CPQ), Harvard Light Exposure Assessment (H-LEA), sun exposure habits, Morningness-Eveningness Questionnaire (MEQ), Positive and Negative Affect Schedule (PANAS), Pittsburgh Sleep Quality Index (PSQI), and Edinburgh Postnatal Depression Scale (EDPS). Meanwhile, anthropometric data such as gestational weight gain and birth outcomes are gathered from clinic record. In addition, data on infant sleep, feeding, behavior, and light exposure will be collected using Brief Infant Sleep Questionnaire (BISQ), infant feeding log, Baby Eating Behavior Questionnaire (BEBQ), Infant Behavior Questionnaire- Revised (IBQ-R), and infant light exposure log sheet. Cortisol levels will be determined using salivary cortisol method where maternal and infant saliva samples are collected at 3 time points: upon awakening, noon (10:00 to 12:00), and evening (19:30 to 21:00). Understanding the potential factors affecting infant circadian rhythm offers new insights in understanding modern lifestyle factors and its association with fetal programming, infant growth, and development.