By which week of fetal development does the baby begin to develop a regular schedule of sleeping, sucking, and kicking?

By the 20th week of fetal development, the baby begins to establish a more regular pattern of activity, which includes sleeping, sucking, and kicking. At this stage, the central nervous system is sufficiently developed to allow for these rhythmic behaviors. Fetuses typically start to exhibit increased motor activity around this time, which can be observed as kicks or movements felt by the mother.

Before this age, while some movement occurs, it tends to be more sporadic and reflexive rather than intentional. By week 20, the patterns become more discernible and can resemble a sleep-wake cycle, indicating further development of the nervous system and the fetus's ability to engage in these activities in a more organized manner. This timing is consistent with what is known about fetal development milestones, making the identification of 20 weeks as a significant point for the establishment of these regular patterns accurate.