“…The minimum number of metabolites for inclusion in the review was five (Sohlberg, Wikström, Olovsson, Lindgren, Axelsson, Mulic-Lutvica, Weis et al), while as many as 8000 features, as defined by their mass (mz) and retention time (rt) were included in the untargeted studies (Kelly, Croteau-Chonka, Dahlin, Mirzakhani, Wu, Wan, McGeachie et al 2016). Of the prospective studies and nested case-control studies, seven analyzed first trimester metabolites (Austdal, Tangerås, Skråstad, Salvesen, Austgulen, Iversen, Bathen 2015; Bahado-Singh, Akolekar, Mandal, Dong, Xia, Kruger, Wishart et al 2012; Bahado-Singh, Akolekar, Mandal, Dong, Xia, Kruger, Wishart et al 2013; Bahado-Singh, Syngelaki, Akolekar, Mandal, Bjondahl, Han, Dong et al 2015; Koster, Vreeken, Harms, Dane, Kuc, Schielen, Hankemeier et al 2015; Kuc, Koster, Pennings, Hankemeier, Berger, Harms, Dane et al 2014; Odibo, Goetzinger, Odibo, Cahill, Macones, Nelson, Dietzen 2011), while only three analyzed second trimester metabolites (Diaz, Barros, Goodfellow, Duarte, Galhano, Pita, Almeida et al 2013; Kenny, Broadhurst, Dunn, Brown, North, McCowan, Roberts et al 2010; Pinto, Maciel, Melo, Domingues, Galhano, Pita, Almeida et al 2014) (Figure 2). …”