An illustration of the methodology. HRV during periods in the incubator were modeled using the first 30 minutes (indicated with an asterisk) of data from the period in the incubator during which, by design, the infant was not being handled, thus yielding normative values of HRV. The first and last 15 minutes of data during KC were excluded; the rest of the period was also used for statistical modeling (indicated with an asterisk). The duration of KC could vary from one session to the other. Tx and Ty represent the periods of transfer from the incubator to the parental chest and vice versa. ‘A’ refers to the first minute on the parent’s chest; ‘B’, to the first minute back in the incubator.