Association between light rare earth elements in maternal plasma and the risk of spontaneous preterm birth: a nested case-control study from the Beijing birth cohort study

Table 2 Comparison of median concentrations of rare earth elements between cases and controls

Trimester	Elements	Case (n = 244)	Control (n = 244 ^a)	P^b
First	La	0.073 (0.059, 0.093) ^c	0.073 (0.058, 0.099)	0.708
	Ce	0.118 (0.085, 0.159)	0.126 (0.091, 0.165)	0.347
	Pr	0.031 (0.023, 0.040)	0.030 (0.024, 0.038)	0.674
	Nd	0.163 (0.113, 0.220)	0.161 (0.115, 0.231)	0.882
	Sm	0.047 (0.021, 0.080)	0.048 (0.024, 0.076)	0.718
	Eu	0.014 (0.014, 0.016)	0.014 (0.014, 0.014)	0.527
Third	La	0.072 (0.055, 0.090)	0.070 (0.052, 0.088)	0.217
	Ce	0.103 (0.073, 0.143)	0.102 (0.071, 0.134)	0.234
	Pr	0.031 (0.024, 0.040)	0.030 (0.021, 0.037)	0.111
	Nd	0.179 (0.115, 0.245)	0.173 (0.118, 0.234)	0.453
	Sm	0.055 (0.029, 0.096)	0.049 (0.022, 0.091)	0.355
	Eu	0.014 (0.014, 0.026)	0.014 (0.014, 0.023)	0.485

^a: In the third trimester, only 243 controls were included because one plasma sample was not adequate for laboratory analyses
^b: Statistical test by the Mann-Whitney U test
^c: Units: ng/mL; Data are presented as “median (lower quartile, upper quartile)”

ISSN: 1476-069X