Table 1 Number and percentage of studies by continent, climate zone, year of publication, population group and income level

	Categories	Number of studies	Percentage
Location of study (continent)^a	Africa	11	5.5
	Asia	68	34.2
	Australia	12	6.0
	Europe	36	18.1
	North America	59	29.6
	South America	9	4.5
	Multiple	4	2.0
Climate zone^b	A: tropical	10	5.1
	B: dry	19	9.6
	C: temperate	79	40.1
	D: continental	21	10.7
	Multiple	68	34.5
Year of publication	Pre-1980	4	2.0
	1980–1999	9	4.5
	2000–2009	17	8.6
	2010–2019	96	48.5
	2020–2023	72	36.4
Population group^c	Maternal	52	23.9
	Fetal and perinatal	51	23.4
	Neonatal	115	52.8
Income level^d	Low income	6	3.1
	Lower–middle income	17	8.7
	Upper–middle income	47	24.0
	High income	126	63.3

^aN sums to 199. One paper (Bakhtisityarava et al.⁷⁸) performs analysis separately on two different continents.
^bN sums to 199. One paper (Qu et al.³⁰) reports estimates for two different climate zones.
^cN sums to 218. Eighteen papers report two outcomes, and one paper reports three outcomes (Khodadadi et al.⁴⁴).
^dN sums to 196. One paper (Bakhtisityarava et al.⁷⁸) included three locations (Brazil, Mexico and Chile) with two different income levels. Three studies (Dieckmann⁷⁹, Jensen and Sørensen⁸⁰, and Wells and Cole⁸¹) were conducted in many countries.

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