Table 1.

Quality assessment of the included studies based on the Newcastle–Ottawa scale.

Study	Selection	Comparability	Outcome/Exposure	Total Score
Krętowska et al., 2019 [34]	***	**	***	8
Pinney et al., 2017 [35]	***	**	***	8
Burstyn et al., 2013 [36]	****	**	***	9
Phillipat et al., 2014 [37]	***	**	***	8
Phillipat et al., 2019 [38]	***	**	***	8
Lee et al., 2014 [39]	***	**	***	8
Lee et al., 2018 [40]	***	**	***	8
Dalkan et al., 2019 [41]	***	*	***	7
Chou et al., 2011 [42]	***	**	***	8
Gounden et al., 2019 [43]	***	*	***	7
Xu et al., 2015 [44]	**	*	***	6
Wang et al., 2017 [45]	***	**	***	8
Troisi et al., 2014 [46]	***	**	***	8
Huo et al., 2015 [47]	****	**	***	9
Ding et al., 2017 [48]	***	**	***	8
Tang et al., 2013 [49]	***	**	***	8
Padmanabhan et al., 2008 [50]	***	**	***	8
Veiga-Lopez et al., 2015 [51]	***	*	**	7
Huang et al., 2017 [52]	***	**	***	8
Mustieles et al., 2018 [53]	**	**	***	7
Aker et al., 2019 [54]	***	**	***	8
Woods et al., 2017 [55]	***	**	***	8
Ferguson et al., 2016 [56]	***	**	***	8
Casas et al., 2016 [57]	***	**	***	8
Snijder et al., 2013 [58]	***	**	***	8

Award of the stars can be found on http://www.ohri.ca/programs/clinical_epidemiology/nosgen.pdf (accessed on 13 July 2021) [59]. In the comparability category the particular confounding factors were gestational age (most important factor) and at least one of the following: maternal age, smoking, educational level, pregestational weight, height, race and parity.