The time around childbirth is an important period in life for the expecting couple. The transition to parenthood has critical psychosocial consequences for both parents, and requires personal adjustments that are not only physical but also mental and social (Feldman, 2015; Sundstrom Poromaa, Comasco, Georgakis, & Skalkidou, 2017). On top of that, the preceding pregnancy is a considerable biological stressor for the mother, triggering and testing her underlying somatic and mental sensitivities (Skalkidou, Hellgren, Comasco, Sylven, & Sundstrom, 2012). One of the most prevalent mental health problems during this critical time period is peripartum depression (PPD), which affects more than 10% of women during pregnancy and/or after childbirth (Biaggi, Conroy, Pawlby, & Pariante, 2016). PPD is defined as a depressive episode starting in pregnancy or in the postpartum period. The disorder is recognized worldwide, with higher prevalence in low‐income and middle‐income countries compared to high‐income countries (Biaggi et al., 2016).

The aim of this In Focus issue is to critically review the clinical literature on PPD, highlight important biological mechanisms that may contribute to onset of PPD, point to important future research areas, and move the scientific field forward by providing recommendations for consensus on PPD research guidelines.

While numerous studies on peripartum depression have been published, Kimmel and colleagues point out that most of the research has dealt with incidence estimates and risk factors, studies are mostly cross‐sectional rather than longitudinal and often underpowered for the investigation of multiple risk factors (Kimmel, Bauer, & Meltzer‐Brody, 2019). Based on the current literature, risk factors can be grouped into two main categories: biological and psychosocial. The biological research mostly focuses on the endocrine system, the immune system, and genetic factors, whereas the psychosocial literature addresses stressors and interpersonal relationships or support. The downside of this bifurcated literature on PPD is that bio‐psychosocial processes and interactions are neglected, and integrative models remain underdeveloped and untested. An important message of this In Focus issue is, thus, to move the field toward wide‐scale collaborations, as it has, already, been done in other fields in medicine (Kimmel et al., 2019).

An important area for future studies is the heterogeneity of PPD and the need for refinement of phenotypes and symptomology. The study by Wikman and co‐workers is a valuable attempt to define the characteristics of different PPD trajectories, comparing women who developed their depressive episodes during pregnancy with those who had an early or late postpartum onset and those who were chronically depressed (Wikman et al., 2019). Their findings suggest that different PPD trajectories have different biological and socioeconomic correlates, most strikingly for the early postpartum onset, which should guide the development of personalized treatments (Wikman et al., 2019).

Frokjaer addresses the endocrine environment of the postpartum period, especially estradiol, as a potential contributor to the onset of depressive symptoms (Frokjaer, 2021). Using a randomized controlled trial on gonadotropin releasing hormone agonist treatment as a model of estrogen change and deficiency, together with multimodal neuroimaging and epigenetic markers, she sets the stage for a cascade of effects that put susceptible women at increased risk of depression. These estrogen deficiency‐induced perturbations include changes in synaptic serotonin, disengagement of the hippocampus and brain regions of the reward circuit, and overuse of emotion processing networks (Frokjaer, 2021).

Presumably induced by hormonal changes, Medina and Workman discuss neurogenesis in the hippocampus and olfactory bulb across pregnancy and postpartum (Medina & Workman, 2018). Their review synthesizes the extensive cross‐species literature, pointing to increased cell proliferation in certain parts of the hippocampus and the olfactory bulb, and decreased neuron survival in other areas of the hippocampus in the postpartum period. In addition, the authors also discuss how the pregnancy‐induced changes tie to maternal behavior and mental health (Medina & Workman, 2018). These findings are incredibly important as we are just starting to unravel structural brain changes also in newly delivered women.

A problematic area in PPD research is the identification of biomarkers, including genetic biomarkers, which has been limited by difficulties in obtaining large enough sample sizes, critical for adequate statistical power. Brann and colleagues have investigated the usefulness of inflammatory markers for prediction of postpartum depression, and identified a set of five markers that individually showed promise for the prediction of PPD with early postpartum onset (Bränn et al., 2018). At the same time, this study is a good example of the problems in this field; since the immune system changes throughout pregnancy and even more after delivery, biomarker development needs to take the timing of assessment and PPD trajectory phenotype into account.

In conclusion, this In Focus issue gives a broad understanding of where we are today in terms of peripartum depression research, and what we need to do in the future (Kimmel et al., 2019). Future research on PPD should focus on expanding large‐scale collaborations, allow for standardization of research approaches, and integrate biological and psychological variables. We need new research definitions of PPD that consider timing of onset and duration. We should focus on individual symptoms like anxiety and anhedonia rather than on diagnostic entities. Finally, future research guidelines must encourage mixed qualitative and quantitative methods and make use of stakeholder advisory councils and women with lived experience of PPD.

分娩前后对准夫妇来说是人生中的一个重要时期。为人父母的转变对父母双方都具有重要的社会心理影响，需要进行个人调整，不仅是身体上的，还包括心理和社会方面的（Feldman，  2015 年；Sundstrom Poromaa、Comasco、Georgakis 和 Skalkidou，  2017 年）。最重要的是，前一次怀孕对母亲来说是一个相当大的生物压力源，触发和测试她潜在的身体和心理敏感性（Skalkidou、Hellgren、Comasco、Sylven 和 Sundstrom，  2012）。在这个关键时期，最普遍的心理健康问题之一是围产期抑郁症 (PPD)，它影响了超过 10% 的怀孕期间和/或分娩后的女性（Biaggi、Conroy、Pawlby 和 Pariante，  2016 年）。PPD 被定义为从怀孕或产后期开始的抑郁发作。这种疾病在世界范围内得到认可，与高收入国家相比，低收入和中等收入国家的患病率更高（Biaggi 等，  2016）。

本期 In Focus 的目的是批判性地审查关于 PPD 的临床文献，突出可能导致 PPD 发病的重要生物学机制，指出重要的未来研究领域，并通过为 PPD 研究达成共识提供建议来推动科学领域向前发展准则。

虽然已经发表了大量关于围产期抑郁症的研究，但 Kimmel 及其同事指出，大多数研究都涉及发病率估计和风险因素，但研究大多是横断面而非纵向研究，而且往往不足以调查多种风险因素（Kimmel , Bauer, & Meltzer-Brody,  2019）。根据目前的文献，风险因素可以分为两大类：生物学和社会心理。生物学研究主要集中在内分泌系统、免疫系统和遗传因素上，而社会心理文献则涉及压力源和人际关系或支持。这种关于 PPD 的分叉文献的缺点是生物心理社会过程和相互作用被忽视，综合模型仍然不发达和未经测试。因此，这个 In Focus 问题的一个重要信息是将该领域推向广泛的合作，因为它已经在医学的其他领域完成了（Kimmel 等人，  2019 年）。

未来研究的一个重要领域是 PPD 的异质性以及对表型和症状的改进的需要。Wikman 及其同事的研究是定义不同 PPD 轨迹特征的宝贵尝试，将妊娠期间出现抑郁发作的女性与产后早期或晚期发作的女性以及长期抑郁的女性进行了比较（Wikman 等.,  2019 年）。他们的研究结果表明，不同的 PPD 轨迹具有不同的生物学和社会经济相关性，最显着的是产后早期发病，这应该指导个性化治疗的发展（Wikman 等人，  2019 年）。

Frokjaer 解决了产后的内分泌环境，尤其是雌二醇，这是导致抑郁症状发作的潜在因素（Frokjaer，2021 年）。她使用一项关于促性腺激素释放激素激动剂治疗的随机对照试验作为雌激素变化和缺乏的模型，结合多模式神经影像学和表观遗传标记，为一连串效应奠定了基础，这些效应使易感女性患抑郁症的风险增加。这些雌激素缺乏引起的扰动包括突触血清素的变化、海马体和大脑奖励回路区域的脱离以及情绪处理网络的过度使用 (Frokjaer, 2021 )。

大概是由荷尔蒙变化引起的，Medina 和 Workman 讨论了怀孕和产后海马体和嗅球的神经发生（Medina 和 Workman，  2018 年）。他们的综述综合了大量的跨物种文献，指出海马和嗅球某些部位的细胞增殖增加，而海马其他部位的神经元存活率在产后降低。此外，作者还讨论了妊娠引起的变化如何与母亲的行为和心理健康相关联（Medina & Workman，  2018 年）。这些发现非常重要，因为我们刚刚开始揭示新分娩女性的大脑结构变化。

PPD 研究中的一个问题领域是生物标志物的识别，包括遗传生物标志物，由于难以获得足够大的样本量而受到限制，这对于足够的统计能力至关重要。Brann 及其同事研究了炎症标志物对预测产后抑郁症的有用性，并确定了一组五个标志物，它们分别显示出预测产后早期发病的 PPD 的前景（Bränn 等人，  2018 年）。同时，这项研究是该领域存在问题的一个很好的例子；由于免疫系统在整个怀孕期间甚至分娩后都会发生变化，因此生物标志物的开发需要考虑评估时间和 PPD 轨迹表型。

总之，这个焦点问题让我们对我们今天在围产期抑郁症研究方面的进展以及我们未来需要做的事情有了广泛的了解（Kimmel 等人，  2019 年）。未来对 PPD 的研究应侧重于扩大大规模合作，实现研究方法的标准化，并整合生物和心理变量。我们需要考虑发病时间和持续时间的 PPD 新研究定义。我们应该关注焦虑和快感缺乏等个体症状，而不是诊断实体。最后，未来的研究指南必须鼓励混合定性和定量方法，并利用利益相关者咨询委员会和具有 PPD 生活经验的女性。