Infant mental health is a public health priority both internationally [
1] and in France [
2]. Mental health disorders in childhood have long term consequences throughout the lives of the individuals in question, their families and the social environment as a whole [
3]. The prevalence of psychiatric disorders in infants is related to a variety of psychosocial vulnerability factors. More emotional and behavioural disorders are seen in children of young, first-time mothers [
4,
5]; in infants with low quality of home environment [
6,
7]; in children of mothers with postnatal depression [
8,
9] or who have less knowledge of infant development [
10], less parenting skills [
11] or insightfulness [
12]; in children of mothers who smoke [
13] or who have other health problems [
14]; in situations of psychosocial parental stress [
15] or less perceived social support [
16]; in children of mothers showing attachment disorganization [
17]; in preschoolers whose parents do not live together [
18]; and in children of families of low socioeconomic status and educational level [
18]. Furthermore, individual vulnerability appears to be linked to the accumulation of vulnerability factors rather than being a direct result of one particular factor [
19].
Health promotion approaches have explored various strategies, including actions within educational settings as well as home-visiting programs, widely developed since the using a model developed by David Olds [
14,
20]. In the USA, services based on these latter programs are today supporting more than 500,000 families [
21]. In Europe, they are increasingly being integrated into existing social and health care systems [
22-
24]. One of the main purposes of home-visiting programs is to act upon the determinants of child mental health, particularly by reducing the impact of social stressors on families [
25-
28], developing parenting knowledge and skills regarding child development [
29] and promoting maternal health [
30], for example in areas such as diet, sleep and substance misuse [
29]. Typically, families receive home visits from qualified nurses or trained paraprofessionals, often from the communities being served, on a weekly or monthly basis, beginning during pregnancy and ending when the child is between two to five years old [
31]. A number of studies have shown home visiting to be an effective strategy for improving child development and parenting in vulnerable families [
25-
28,
32], and reducing the risk of child abuse [
28]. However, in recent reviews of these programs, only one in two demonstrate significant and positive impacts on children [
24,
33], a phenomenon often attributed to variation in implementation practices [
33,
34], to difficulties engaging families [
35] or to using home-visiting personnel who are insufficiently trained [
30].
The CAPEDP (Compétences parentales et Attachement dans la Petite Enfance: Diminution des risques lies aux troubles de santé mentale et Promotion de la résilience - Parental Skills and Attachment in Early Childhood: reduction of risks linked to mental health problems and promotion of resilience) study is the first randomized, controlled trial assessing an evidence-based, home-visiting program in France. Towards the end of the 1990s, despite the existence in every neighborhood of government-run mother-child services as well as community mental health services for both children and adults, mental health professionals had been becoming increasingly concerned by the number of children living in vulnerable social situations being referred for care, typically for behavioural problems. An international conference [
36] confronting evidence-based preventive programs from different national contexts provided the impetus for developing the first French home-visiting program specifically targeting infant mental health, in line with international best practice criteria [
24,
32,
37,
38], and adapted to the particularities of the French context. The resulting CAPEDP project involved designing, implementing and evaluating an early, long-term, supervised, home-based intervention targeting the determinants of infant mental health in families presenting multiple psychosocial vulnerability factors.
The CAPEDP program has two major specificities with regard to most other home-visiting programs. The first specificity was to address child mental health promotion in families that already have, at least theoretically, free access to one of the most extensive, comprehensive and longstanding social and health care systems in the Western World. Indeed, at the close of World War II, France developed nation-wide, community-based, mother-child support and prevention services with no out-of-pocket payment, known as the
Protection Maternelle et Infantile (Mother and Child Protection Services or PMI). Today, mothers have direct access to PMI centres free of charge from the beginning of pregnancy right through to their child’s third birthday. France was also the first Western country to develop, across the country, free community mental health services for both adults and children. With regard to child and adolescent care, each community mental health service provides care with no out-of-pocket payment for a population area of an average 250,000 inhabitants and, although with limited resources, being able provide home visits if deemed necessary for the child’s mental health or safety. Families also automatically access specific social benefits (
allocations familiales) provided by local government to help raise their children, if they accept to bring them in for a limited number of health check-ups and compulsory vaccinations. Furthermore, families identified by maternity ward staff as being particularly vulnerable will receive home visits by PMI nurses - although a 2002 study revealed that, in the majority of cases (60%), this happened only once and only 7% of these more vulnerable families received more than three home visits [
39]. Although PMI nurses receive no specific training on mental health promotion or prevention and little organised psychological supervision, they can and do refer families directly to their local community child and adolescent mental health service. As for the PMI, the functioning, outcomes and cost/efficiency of these mental health services have undergone little systematic evaluation.
The second major specificity of the CAPEDP intervention was that the entire home-visiting program was conducted by qualified psychologists. It was hypothesised that professionals who were more highly trained in psychology would be more competent in recognizing the elements in play with regard to the determinants of infant mental health and more skilled in acting upon these determinants.
Objectives
The aim of the CAPEDP trial was to evaluate, in young primiparous mothers presenting vulnerability factors associated with greater likelihood of child mental health disorders, the impact on infant mental health of a home-visiting program conducted by trained psychologists and targeting the major modifiable determinants of infant mental health.
The program evaluated three primary outcomes: child mental health at the age of two, as well as two potential mediating variables: maternal postnatal depression at three months postpartum and the quality of the home environment when the child was 12

months old.
Secondary objectives included evaluating the impact of the intervention on: maternal postnatal depression at 6

months postpartum, infant attachment quality at 18

months of age, the mother’s quality of attachment at her child’s second birthday, her knowledge and use of social, medical and educational support services, her perception of receiving support from her own personal network, her parenting perceptions and behaviour, the child’s psychomotor development, sustained withdrawal behaviour of the child at 18

months, the mother’s knowledge concerning child development, her parental stress concerning caring for her child, her access to training and employment, her own psychological health and, in the intervention group, the working alliance between the mother and the home-visiting team (Table ).
| Table 1Outcome criteria and assessment schedule |
An ancillary study: the CAPEDP-A Study
Assessment of attachment security and caregiver behaviour being particularly complex from a procedural point of view, an ancillary study involving a subsample of the CAPEDP population was designed to investigate this particular point: the CAPEDP Attachment (CAPEDP-A) Study. The objectives of this ancillary study were to assess the impact of the CAPEDP intervention in terms of increasing infant attachment security and maternal reflexive ability and reducing infant attachment disorganisation and maternal disorganizing behaviour when the child was from 12 to 15

months old.