Randomization and Blinding
Couples are randomly assigned to the three treatment conditions (low dose, high dose, waiting list control) after completing measures at T1 by the study coordinator using block randomization of 10 couples per group. In case of logistical and administrative problems (trainings are only deliverable at two sites) couples are randomly assigned to the low-dose or control condition. Participants are informed about group membership via e-mail after randomization. Except from study coordinators, all involved researchers, data collectors and behavioural coders are blinded about group membership. They are not unblinded under any circumstances.
High dose intervention (skills training)
The high dose intervention group participates in the Couple Care and Coping for Parents programme (CCC-P), which is a blend of two evidence-based relationship education programmes: the Couples Coping Enhancement Training (CCET)  and Couple CARE for Parents . CCC-P is a one-day workshop, delivered by a licensed psychologist at the 30th week of pregnancy. The workshop consists of psycho-educational and self-reflection elements and a strong focus on the behavioural training of relational skills (communication, dyadic coping, problem-solving, self-regulation in relationships). With respect to specific needs during TTP, additional topics are addressed (i.e., role changes, task distribution, sleep and sexuality after birth). The core components of the workshop are dyadic exercises, where couples are prompted by trained psychologists (ratio: two couples per one trainer) in improving their communication, dyadic coping and problem solving . Three types of conversations are trained (couple conflict (internal stress), positive experience with the partner (wishes) and an external stress experience, meaning an individual stressor of each partner). To promote constructive communication, both partners are alternately in the role of speaker and listener and are encouraged to apply speaker and listener rules. For strengthening stress-related self-disclosure, listening and appropriate dyadic coping, couples are trained in the three-phase-method . Within problem solving, couples learn the six-step-problem solving technique . To ensure full privacy, each couple performs the training exercises in separate rooms. Couples are coached in every second conversation. During the five home visits, a midwife continues the skills training at couples’ homes (2 hours). Additionally, partners receive self-reflection and self-regulation tasks about a certain topic (e.g., infant care, parental self-efficacy, affection and sexuality, division of labour, expectations regarding the future).
Low dose intervention (psycho-education)
Participants in the low dose group are asked to watch an interactive movie, including psycho-education on changes related to TTP. Short theoretical inputs are rounded off by narrated experiences of six couples that recently became parents and talk about changes related to the birth of their child with regards to sleep and energy, household division, mutual support, and sexuality. The movie aims at increasing couples’ awareness of challenges emerging during TTP and contains tips on relational skills, but no coaching exercises. At the end of the movie, ideas about how to implement gained knowledge into daily life are provided. Each couple receives an individual access code via e-mail to stream the movie or a hard copy if preferred. To check if couples watch the movie, the online access to the movie is tracked and couples are asked questions about it.
Waiting list control
The waiting list control condition consists of the treatment as usually offered by hospitals after the birth of the child (TAU) and contains no comparable intervention elements of the couple-focused intervention as offered to the low and high dose group. After completion of the first nine time points, couples in this group can either watch the movie or participate in the workshop.
We investigate treatment as usual as a control group to establish the natural development of relationships to which we can compare the development with the intervention.
Adherence to CCC-P (high dose intervention)
All workshop providers receive an intensive training and need to be licensed to deliver CCC-P. Psychologists are recruited from trained and licenced CCET providers. Midwives receive a specific CCC-P training and need to successfully pass a final exam. CCC-P-sessions are delivered upon a standardized manual and checklists. Protocol adherence is evaluated by audiotapes of home visits and specific checklists regarding the content that has to be delivered. Further, midwives receive supervision and individual feedback based on the audiotapes.
Primary study outcomes are directly targeted by the intervention, such as relational skills, individual and relational well-being and coparenting. We hypothesize that secondary outcomes, which are child-related outcomes, will be indirectly affected by the intervention through various skills (see Figure 1). This is a multimodal study using self- and partner-report as well as behavioural observation for primary and secondary outcomes. All variables are assessed with standardized scales, observational situations, and coding systems with approved psychometrics. Instruments developed by the authors will be evaluated for reliability and validity. In case of a lacking German translation, the standard procedure is applied (translation—back-translation—evaluation and adaptation). Figure 3 presents the outcome measures and the time of application.
Figure 3. Schedule of enrolment, interventions, and assessments.
Primary outcomes (variables targeted by the intervention)
Relational skillsare assessed by self- and partner report of communication withthe Marital Communication Questionnaire (MCQ)  measuring positive and negative marital communication behaviours in romantic relationships according to the SPAFF coding system  and of dyadic coping with the Dyadic Coping Inventory (DCI)  measuring communication of stress, supportive dyadic coping, common dyadic coping and negative dyadic coping. Self-regulation in relationships is assessed with the Self-regulation for Effective Relationships Scale (SRER)  measuring the degree to which partners are working toward a successful relationship. Observations of relational skillsare conducted by trained examiners who visit couples at home and ask them to have three eight-minute conversations. To assess couples’ stress and coping behaviour they are asked to talk about each partners’ recent most stressful external stress experience. Therefore, each partner evaluates the burden of different areas of external stress. The sequence of whose topic will be discussed first is randomized across couples. Conversations are held in private. To assess couples’ conflict communication for the third conversation both partners rate the impact of different areas of internal stress and choose one for the conflict discussion. Couples are invited to behave as they usually do. As known from international research, these conversations show high ecological validity.
Individual skills are assessedwith the German translation  of the BriefCOPE questionnaire  measuring effective and ineffective individual coping strategies and the Negative Emotion Regulation Inventory (NERI)  measuring individual parental emotion regulation and the intensity of emotional experiences in situations commonly inducing fear, anger, and sadness .
Individual well-being is measured with psychopathological symptomatology assessed with the Depression, Anxiety and Stress Scale (DASS-G) , parental Stress is assessed with theParental Stress Scale (PSS)  measuring positive and negative aspects of parenting and emotional vulnerability withthe short version of the Emotional Vulnerability Questionnaire (EVQ)  measuring the intensity and frequency of feeling hurt.
Relational well-beingis assessed withthe Couples Satisfaction Index (CSI)  and the German version  of the Relationship Assessment Scale (RAS) , measuring relationship satisfaction and with the German version  of the Marital Satisfaction Inventory (MSI)  and the Sexual Activity Scale , measuring sexual satisfaction.
Coparenting skills are assessed with the Coparenting Scale for Parents with Preschool Children (CSPPC) , measuring parental cooperation, differences and conflict, triangulation and undermining.
Secondary outcomes (indirect or long-term outcomes).
Child outcomes are measured with both parent-report of sleep problems with the Brief Screening Questionnaire for Infant Sleep Problems (BISC) , parent report of eating and screaming behaviours of the child with a scale developed by the authors measuring breastfeeding or bottle-feeding behaviour, eating and screaming behaviour of the child and subjective disturbance. Emotional and behavioural problems in early childhood are assessed with the German version  of the Early Childhood Screening Assessment (ECSA) , measuring child internalizing and externalizing symptoms. Behavioural problems with peers are measured with a subscale of the German version of the Strengths and Difficulties Questionnaire (SDQ) . Emotional competency of the child is assessed with a subscale of the KOMPIK . Parent-child interactions are assessed by two examiners who videotape the family at home during seven experimental situations. Parent-child emotion regulation is assessed with situationeliciting fear (stranger approach, remote control spider) and anger (toy removal, losing game) in the child [61–63]. Child autonomy and parental autonomy support are assessed with one triadic (clean-up task) and two dyadic interactions tasks (semi-structured play task) with each parent separately [46, 64]. Child Attachment Security to each parent is assessed using the Attachment-Q-Sort (AQS)  based on videotapes of the complete home visit, including separations, reunions and additional information from the parents. Children’s emotional reactions during the tasks, will be coded based on a standardized coding system, which was reliably used in previous studies [46, 64].
Background information is collected with a broad variety of control variables that might influence outcome measures. Couples will provide information about their age, gender, nationality, marital status, relationship duration, type of residence, current pregnancy, education, profession, and employment status (including hours per week spent at work) as well as their attitude towards pregnancy, parental support, time for leisure, family, child and work, household task division, attachment, positive parenting, stress, and mood state.
Several trained coders independently code maternal, paternal, and child’s behaviours videotaped with the parent-child and couple interaction tasks. Couple interactions and parent-child interactions are coded by different teams. Training continues until inter-rater reliability (ICC>.80, Kappa >.60) is reached.
In the dyadic interactions, dyadic coping is coded with the System for Analysing Dyadic Coping (SDAD) , which allows micro-analytic coding of stress communication and dyadic copingand conflict communication behaviour (positive and negative behaviours and affects) is coded with the SPAFF . Each category is coded independently for women and men by one coder per subject.
In the parent-child interactions, emotional reactions of the child at facial, vocal, and behavioural level are rated based on a coding system developed and tested in a previous study . Latency, intensity, duration, and quality of emotion are observed in the course of all triadic situations. Child Autonomy is coded based on standardized coding systems developed and tested in a previous study . Parental Autonomy Support and sensitivity in a play context are coded by use of the Sensitive and Challenging Interacting Play scale (SCIP) . Maternal and paternal responsiveness, scaffolding, cooperation, as well as overall sensitive challenging interactive play are coded during the course of the ten-minute play interaction. Attachment Security is coded for each parent separately by use of the Q-Sort procedure resulting in continuous scores for security and dependency. Meta-analytical evidence shows the validity of the resulting security score .
Participants’ names are linked to research identifiers in one file, which is only available to the main researchers and password protected. All data is safely stored at the universities using research identifiers only, stored in locked cabinets and password locked hard disks in rooms only accessible to the research team. Each team member signs the Confidentiality Declaration of the University of Zurich (see Appendix). Data collectors will not have access to data and data coders to names or addresses of participants.
Based on previous experiences, the missing rate and dropout can be minimized by systematically engaging with the sample (e.g., Christmas cards, birth day cards, newsletters about study progress). Depending on the missingness mechanism  for drop-outs and/or missing measurement occasions, we will adopt different missing data management strategies.
Besides standard statistics, approaches that account for nested data structure are required, including Multilevel Modelling, Structural Equation Modelling, and the combination of both. These analytic strategies allow for simultaneous estimation of longitudinal models with nested data structures, which occurs when couples are examined over several time points. Analysis and presentation of data will be in accordance with the CONSORT guidelines.
A Data Monitoring Safety Board does not seem warranted, as we do not conduct a pharmacological study. Completeness of data will be checked after participation. Comments of the participants are used to improve data collection constantly. Data collectors meet regularly to exchange experiences and problems and to ensure adherence to protocol.
First interim results will be possible after T9, when the interventions are terminated.
As the current intervention is a psychological not a pharmacological intervention, no adverse effects are expected. However, participants are told verbally and in writing to contact study coordinators at any time if there are questions or any inconvenience. Throughout the study, a psychotherapist is on constant call for participants. Data collectors have contact details with them if requested by participants and are told to report unusual experiences to study coordinators immediately.
The investigators organize workshops. Evaluations by participants and feedbacks from data collectors will be reported after each workshop. Investigators will collect and control audio recordings of home visits.
If substantial amendments will be needed, they will be notified to the internal Ethic Committees of the Philosophical Faculty of the University of Zurich. Non-substantial amendments will be recorded.
Ancillary and post-trial care
Participants can contact study coordinators if interested in further care. In this case an initial interview with a couple, child or individual psychotherapist will be sponsored by the study.
Data processing will be divided between investigators in accordance with their research focus and the authorship regulations. Results will be published in peer-reviewed scientific journals in accordance to international standards. Participants will be informed about results and conclusions.