Hair Cortisol as Marker of Chronic Stress in Preterm and Term Fathers - Fathair-study

The goal of this observational study is to compare the paternal hair cortisol as a marker for chronic stress in prematurely born children to maturely born children. The main questions it aims to answer are: * How differ the cortisol level between groups? * How change the cortisol level over time? * Are there secondary outcomes associated to the cortisol level of fathers? Participants will give a hair sample to analyse the cortisol level and fill out questionnaires at three time points. At six months of the infant's age, the investigators will also measure the paternal sensitivity.

For expectant parents, the birth of a child is often a stressful situation. In the case of a premature birth, the psychological stress is usually increased because the parents frequently could not prepare for the birth. Therefore, the researcher would like to investigate this stress of fathers of newborn children. For this purpose, the stress hormone cortisol in the fathers' hair will be analysed and questionnaires on the fathers' mental health will be collected. Subsequently, the differences between fathers of prematurely born and of maturely born children will be compared. The investigators will do the analyses at three time points: the first time point will be at the first week after birth, the second three months and the third six months after birth. At six months of the infant's age, additionally the paternal sensitivity will be measured. The compared groups will differ with respect to gestational age: Group 1 includes preterm infants with a gestational age below 32 weeks and a birth weight \<1500 grams (very low birthweight infants), group 2 preterm infants with a gestational age between 32 0/7 to 36 6/7 (moderate and late preterm infants) and group 3 consists of mature infants (over 37 weeks gestational age).