\<Ethical considerations\> This research protocol was approved by the Ethics Committee of Nagano Children's Hospital before this research is being conducted. Recruitment is undertaken by the neonatologists in the unit. They provide written and oral information about the study when they explain infants' condition to their parents at admission. The parents are given sufficient time to consider their participation. The informed consent will be asked within 7 days from the birth, otherwise the infant will be excluded from this study. At least one of the parents should sign the informed consent before enrolment. At the time of agreement, investigators give the infant an anonymous number to protect personal information.
\< Power calculation \> The sample size should be decided by the number of parents as the primary outcomes are for parents. Investigators plan to include 110 couples or families; the power calculation showed that investigators could detect a 2.5 difference in the mean Edinburgh Postnatal Depression Scale (EPDS) score of longer and shorter presence groups (with power 0.8 and alfa 0.05) with this number of parents.
\<Measures and data collection\> Diary record Parents make a record on daily diary from the next day of agreement to one day before discharge. Parents make a record about duration of these four topics; presence, skin-to-skin contact (SCC), participation in infant care, and any other interaction with their infants.
* "Care taking" includes the followings; breast feeding, bottle feeding, milking, tube feeding, changing diaper, wiping body, bathing, and any other essential care for baby. However, any care taking during "SCC" mustn't included in this section.
* "Other interaction with baby" includes the followings; hugging, holding, touching, watching, talking, reading books, playing, making something or writing diary for baby, and any other approaches for baby. However, any interaction given during "SCC" or "care taking" mustn't included in this section.
Investigators use the modified Parent-Infant Closeness Diary. The original diary includes three items for each mother and father; presence, holding and SCC. Investigators have changed these items into our own settings as above and changed the used language into Japanese. Investigators already have got the permission from the developers of this diary. This diary has one day per page including all the four topics for both parents. Mother and father respectively draw a line on the blank of specific items they do. They should fill all the corresponding blanks when they do things for multiple babies. The start and the end times should be put in 5-minute increments. The validity of Parent-Infant Closeness Diary has already been proven.
Perinatal Data Collection Perinatal information of the infant includes sex, gestational age, birth weight, height, head circumference, mode of delivery, parity and plurality of mother, and Apgar score at 1, 5, and 10 minutes. Investigators will also find out if the infant meets the criteria for small for gestational age (SGA), which is defined as both birth weight and height are \<10th percentile.
Perinatal information of the family members includes the first meeting days with the infant and the first SCC days, for mother and father respectively.
Background information of the family includes family composition, presence of mother's supporter, the number of siblings living with parents, and required time from home to the hospital.
Background information of the parents includes the age, the educational background, the smoking history at pregnant, occupation and parental leave, history of depression or any other mental health problem before and during pregnancy and the history of medication for that disease, and the degree of social support, which is measured by the Multidimensional Scale of Perceived Social Support (MSPSS) as mentioned below. These are risk factors of postpartum depression.
Short version of Multidimensional Scale of Perceived Social Support in Japanese (MSPSS-Js) The Multidimensional Scale of Perceived Social Support (MSPSS) is widely used self-report measure of subjectively assessed social support. There have been several modifications for MSPSS and now it consists of 12 questions with 7-point rating scale ranging from very strongly disagree (1) to very strongly agree (7) for each question. There is Japanese version of MSPSS (MSPSS-J), whose reliability and validity have proven. Investigators use short version of MSPSS-J (MSPSS-Js), which consists of only 7 questions with 7-point rating scale ranging from 1 to 7 and has high correlation with full version. The total score varies from minimum 7 to maximum 49, and higher scores indicates to have better social support.
Data Collection of the clinical course The information of the clinical course includes days of invasive ventilation, days of non-invasive ventilation, days of any respiratory support including oxygen, the history of patent ductus arteriosus (PDA) operation, the history of surgical treatment of abdomen, age of full feeding (the amount of enteral nutrition \>=100ml/kg/day), the history and the degree of intraventricular hemorrhage (IVH), and the history of retinopathy of prematurity (ROP) treatment.
Evaluation at 36 weeks postmenstrual age (PMA) and discharge Investigators measure the weight (g), height (cm), head circumference(cm), the frequency of breast feeding (per day), and the type of nutrition (exclusive, partial, or no breast milk) at 36 weeks PMA and when the infant discharges home or leaves our NICU to another hospital or ward to prepare for discharge. Investigators also calculate the length of hospital stay (days) and the growth rate of physical measurements between the time of admission and discharge. If the infant leaves our NICU before 36 weeks PMA, investigators use the data at that point as an evaluation at 36 weeks PMA.
The Edinburgh Postnatal Depression Scale (EPDS) and Japanese version of Mother-to-Infant Bonding Scale (MIBS-J) for mother and father All mothers and fathers of the infants enrolled in this research undergo the Edinburgh Postnatal Depression Scale (EPDS) and Japanese version of Mother-to-Infant Bonding Scale (MIBS-J) at least twice. Almost all mothers who deliver in Nagano Children's Hospital usually undergo the EPDS and MIBS-J at 2 and 4 weeks postpartum at the maternity outpatient clinic. Investigators additionally carry out the EPDS and MIBS-J for fathers in NICU once within a month postpartum, and for both fathers and mothers at discharge of their infant for the purpose of this research.
The EPDS is a screening method for mothers to detect postpartum depressive symptoms. It comprises 10 self-report items, each of which is scored on a four-point scale (0-3). The total score varies from minimum 0 to maximum 30, and higher scores indicates to have more depressive symptoms. Investigators use Japanese version of the EPDS, whose reliability and validity have already proven. The cutoff score for Japanese people to indicate probable major postpartum depression should be eight and nine, which is lower than that usually used in western countries.
Mother-to-Infant Bonding Scale (MIBS) is an assessment method for the feelings of a mother towards her new infant, but investigators use Japanese version of MIBS (MIBS-J), whose reliability and validity have already proven. MIBS comprises eight self-report items, but MIBS-J have ten self-report items, each of which is scored on a four-point scale (0-3). The total score varies from minimum 0 to maximum 30, and higher scores indicate a problematic bonding between a mother and her infant.
The main risk factors of mothers' postpartum depression are prenatal depression and anxiety, previous depression or other mental problems, lower income and occupational status, multiparity, presence of other children, poor marital relationship or without partner, lack of social support, stressful life events, negative image toward pregnancy, and experiences of early mother-infant separation. In addition, the risk factors vary depending on when to evaluate postpartum depression. The depression scores in mothers and fathers of preterm infants is at its highest just after delivery and will reduce over time, which shows different change compared with term birth. This is why investigators have to adjust these confounding factors when investigators evaluate the EPDS and MIBS-J of the parents.
Long-term developmental assessment after discharge (birth weight \<1500g) The development of the infants whose birth weight \<1500g are assessed by Kyoto Scale of Psychological Development (KSPD) at 6 and 18 months of corrected age, and 3 years old at the outpatient clinic of Nagano Children's Hospital. KSPD is one of the assessment methods to evaluate developmental quotient and it is known to be well correlated with Bayley III. KSPD consists of three subscales: Cognitive-Adaptive, Language-Social, and Postural-Motor.
\<Outcomes\> The primary outcomes are the EPDS and Japanese version of Mother-to-Infant Bonding Scale (MIBS-J) of the parents. Investigators hypothesize that longer parents' presence decreases the EPDS score and MIBS-J score. Investigators will divide mothers and fathers into two groups respectively (longer and shorter presence groups) based on the distribution of the time of parents' presence, and compare the difference of the mean EPDS score and MIBS-J score between these two groups at each point in time measured.
The secondary outcomes are the followings; (1) length of stay (days), (2) physical measurements at 36 weeks (g or cm) and growth rate from birth to discharge home (g or cm /d), (3) breastmilk-feeding (exclusive, partial, or no breast milk) and the frequency of breastfeeding directly from breast at 36 weeks PMA and at discharge (average frequency per day), and for the infants whose birth weight \<1500g only, (4) developmental quotient (DQ) at 6 and 18 months of corrected age, and 3 years old assessed by KSPD. Investigators hypothesize that longer parents' presence, SCC, participation in infant care, or any interaction with infant improve these outcomes. Investigators will divide mothers and fathers into two groups respectively (longer and shorter presence groups, SCC, participation in infant care, or any interaction with infant) as mentioned above and compare the difference of these outcomes between these two groups. In addition, investigators also correct the data from the diary as the followings; presence of at least one of their parents, SCC with at least one of their parents, participation of at least one of their parents in infant care, and any interaction with at least one of their parents, and consider the outcomes in the same manner. Investigators will also consider (5) the difference of the mean EPDS score and MIBS-J score between longer and shorter SCC, participation in infant care, or any interaction with infant groups.
\<Statistical analysis\> As a statistical analysis, investigators will use a mixed effect model for the EPDS score and MIBS-J score, a linear regression model for other continuous variables (length of stay, physical measurements, growth rate, the frequency of breastfeeding and DQ), and a logistic regression model for binary variable (type of nutrition). Potential confounders will be adjusted.
