Semi-directive interviews lasting 60 to 90 minutes were conducted by a social psychologist trained inresearch and not involved in a NICU. Audio recordings of the interviews were made, with the parents' oral consent. Fathers and mothers were interviewed separately. The interview guide was developed from a review of the literature and from 10 preliminary interviews discussed within focus groups of caregivers, conducted by the researchers. During the interview, parents were encouraged to describe freely how they had experienced the news that the birth would be preterm, the actual birth, and the child's admission to and stay in the NICU. They were encouraged todevelop in detail everything that had helped or hindered them in developing a bond with their baby, as well as the activities set up by the caregivers (see the more detailed description of the interview outline in Additional file 1).

Discourse analysis was used to study the interviews 27 . The analysis was performed separately by a research psychologist and a research assistant. They conducted a horizontal analysis, with immersion and manual coding of the themes in each interview, and a vertical analysis that compared the themes throughout the corpus, identified the convergences and divergences of the same theme across different interviews and developed interpretative hypotheses. Particular attention was paid to the emergence of new themes and contradictory results as the interviews and analysis progressed and data saturation occurred.

The child's medical data and the parents' medical and sociodemographic data were collected from the medical files before and at the time of the interview.

Most parents described themselves as dependent on the staff to care for their baby and therefore necessarily subject to its authority: "As we are in a place where everything is managed by others and we don't know, we have the impression that we have to ask for permission to touch him" (m17). Nearly all the parents reported that the caring and considerate conduct of the staff was primordial for the interactions they developed with their child. Both mothers and fathers reported that a gentle attitude towards their child attenuated the strangeness of the intensive care unit: "There are extraordinary nurses, they talk all the time to the baby, 'my sweetheart, I'm going to do this for you.' I love it that she is in such good hands" (m13). Parents described their ability to have contact with the baby linked to the nurses' conduct, because it made the contact possible (or not) and pleasant (or not). Most parents reported a good relationship with the nurses, who anticipated their expectations and had a gentle attitude toward both parents and baby: "There are disparities between the nurses in terms of their characters and their ways of seeing things. Some are very affectionate with the babies, they give parents lots of information. It's great because it creates a human bond" (m5). A gentle attitude towards the child when providing care encouraged the parents to stay close. "The nurse who talks to my daughter and doesn't make brusque gestures … that makes us want to stay" (m5). A minority stressed more distant and colder nurses: "There are others, there's not much of a relationship. They wait for us to ask questions, and their answers are very terse" (m5). Some added that it felt appropriate to take moments of closeness to their child only when the nurse was kind enough to offer them. Some mothers reported feeling judged by the nurses: "I have the impression of being judged if I call too often … and if we don't come, I'm also afraid of being judged" (m8). They therefore behave differently than they would spontaneously. Globally, mothers described themselves as simultaneously dependent on and close to the nurses, while fathers commented more on the nurses’ behavior towards their children and wives than towards themselves.

Communication with the caregivers appeared decisive for fathers and mothers in feeling a bond with their child. Communication included the content of information exchanged, but also the relationship that existed in those moments. Globally, the consistency of communication was always reported as essential. Throughout the stages from the prenatal period to the first weeks in the NICU, mothers and fathers described expectations that were often similar, and sometimes different. Some fathers reported that the staff spoke to them less than to the mother, which seemed normal or more rarely, frustrating in their role of father.

- In the prenatal period, an exchange with a neonatologist, mentioning the baby's approximate weight and height and a possible relationship with him, triggered the first perception of themselves as parents — father or mother: "The pediatrician told me that he knew how to take care of this baby and that opened a door to the future because two weeks before, the ultrasonographer had told me to separate myself from him" (m3). On the other hand, the existence of discordant information about the thresholds for resuscitating preterm babies was described as very upsetting: not knowing if the child would live or not prevented parents from perceiving themselves as such.

- In the delivery room, mothers reported that they had needed explicit communication — words — about the baby's health, to be reassured that he was really alive: "As soon as I woke up, I asked: He's not dead? He's not dead?’ They told me right away that my son was alive" (m19). Seeing the child, even briefly, was also described as an occasion of feeling like a mother. The fathers talked about the delivery as a moment of intense stress with simultaneous worry for their child and their wife: "Paradoxically, I was more worried for my wife than for my daughter" (f14). Several reported not having been able to feel close to their baby until they had been reassured about their wife's health: "Just after the birth, I went to see my baby with the pediatrician (.) My wife, I was thinking of my wife. It was hard for the baby but I saw him without really appreciating it" (f18).

- After the delivery, many mothers reported having had to wait a day or two before being authorized to see their baby, for health reasons. The photograph of the baby and the NICU caregivers' visit to the mother's room were the two factors described as very useful for feeling closer to the child in these cases. Almost all the parents reported having received a photograph in the first hours after birth and they appreciated it: "It was good to have this picture. I had two feelings…I was glad and sad at the same time…sad because she was premature" (m9). The fathers saw it especially as helpful for their wife, and indirectly for themselves: "I would have liked my wife to have had a picture from the beginning because for the mothers who cannot see their babies, it's the best solution. She's the mother, she needs to see her baby. I reassured her as much as I could" (f11). They also mentioned the photograph as the evidence of a humane attitude by the caregivers: "I thought that was nice, it showed the mind-set of the nurses; I understood then that they didn't care only about the medical care but also about the attachment between parents and child" (f2). The quality of the photograph had to be good, otherwise it would reinforce the harshness of the preterm birth. Several parents described their poor experience with caregivers who promised a photograph that they finally never gave: this unkept pledge reinforced the absence for mothers and created a feeling of impotence in fathers: "I was a little disappointed because a midwife had told me a photo would be taken, and that never happened. I think that would have helped me, if it had been printed right away" (m4). Both parents also reported the supportive value of a visit by the pediatrician or the nurse to the mother's room, telling them about the baby's health. Some mothers saw it as the occasion of their first meeting with the NICU team: "For 3 days I wasn't able to see my daughter. The doctors came to see me and the nurse also. I found that encouraging: I was very glad to get news about her. The information was clear; they told me that she is small but doing well. She has a catheter, and a feeding tube for eating. Otherwise, we know she's alive, but we don't know how she's doing, it's just total darkness. Their coming cheers me up, and that night I slept well. Saying to myself that she's doing well" (m11). On the other hand, the absence of such visits was described by many mothers as a source of isolation and stress and an obstacle to their self-representation as mothers. Many mothers said that they were frustrated to have to rely on the child's father for new information: "It would have been good if someone from the team had come down to see me, because my husband is not a physician. If the NICU nurse had come and said to me, "I'm the one who saw her first, I did this to her. Had she come for two minutes, that would have reassured me still more because they are the ones caring for my baby" (m5).

- Most mothers and fathers needed a caregiver to receive them for the first visit to the NICU, perceived as very stressful: "You come into this grim place; you need someone to say to you, 'you'll see, it's a little strange, a little dark, but that's normal,' because at the beginning, what's dark, is death" (m28). The fathers accompanied their child from the delivery room but frequently described an anxious wait at the ward entrance: "I would have liked it, when I arrived in the unit, for someone to come out and say to me, 'Your daughter is in good hands, we are going to take care of her‘, just to reassure me that everything was all right. And then I would have had some news for my wife; I didn't have that" (f23). Many mothers mentioned their difficulties in reporting what had been said at their first visit, but the attention of the caregiver, perceived by her presence and words, had reassured them: "I don't remember very well what the nurse said to me, but I know she said, don't worry if that goes off. I admit, I've forgotten a lot, it was a very particular moment" (m22). They mentioned that it had been important to them that the nurse introduced herself by her first name — "I'm X, and I'm taking care of your baby" — with a pleasant attitude. Fathers, on the other hand, remembered the information quite clearly.

- In the first weeks in the NICU, access to regular explanations helped most of the parents to limit their feelings of helplessness and to be able to come see the baby day after day. To be at ease with their child, the parents reported that they needed to understand the environment: "The more I know, the more I am reassured. What I want to know are the upper and lower limits, because I watch the monitor and I have the impression I understand" (f23). The mothers saw a need to be reassured when they were holding their child: "At the beginning of skin-to-skin, I didn't really know what was going on: when it rings, for us, that's disastrous, so if you don't see someone come, you say to yourself, but what's going on? In fact, there are alarms that are not so serious, but they hadn't told me, so it would be good if they said at the beginning what it means" (m11).

The mothers said more frequently than the fathers that they needed explanations of the baby's relational capacities and on the meaning of their reactions, to help them: "It's important to understand her reactions, when she cries or seems nervous. If I don't manage to calm her, I feel like a bad mother who does not understand her child. It's important to understand and also to know what to do next" (m15). Fathers and mothers both insisted on the need to warn them of changes such as intubation, changing the room, or placing a catheter: "I arrive, there are 3 physicians in the room, a blue sheet over my baby. And there, I panic! The doctors say to me, "You can't come in." I say to myself, they've put this sheet so that I can't see… They're taking her to the morgue. Fortunately, there was someone who saw that I was stunned and explained to me: They're changing the catheter‘" (m30). Any situation that was unexpected or not understood created a feeling of panic and kept them from spending peaceful time with the baby. They also described their need to not be kept waiting about exam results, such as ultrasound: "If there is no problem with the examinations, the doctors don't come to tell you the results. (.) If they tell us the results right away, whether they are good or bad, we know them and we can start to enjoy the child" (m18).

Some mothers described a feeling of moving backwards in their bond with the baby when his condition grew worse: "What is a little frustrating in the relationship, it's that I had the impression that there was more interaction at the beginning than now, because she has an infection so she isn't very responsive, while before, she took my hand. I arrive, she is grumpy, she cries, so I don't know if it's something to do with me … so I say to myself, ″Oh! I'm not going to come anymore" (m13). The telephone was described as a way of staying linked to the baby from home. Most parents reported feeling reassured by ritualized calls morning and evening: "It's very good to have news by telephone… it takes 15 seconds but afterwards, you feel so much better… then pffff! I pump my milk and I fill the bottle" (m7). Some described calls more worrisome than reassuring, in cases where the phone rang repeatedly with no answer, and stressed the importance of always giving news, even succinctly. Most parents preferred to go home at night rather than stay in a room at the hospital, because it helped them to regain their bearings.

The caregivers’ actions reported by parents as useful for early bonding with their preterm newborn are listed in Table 2.