Table 4.

Transfer efficiencies (%) of PFAS from maternal serum at delivery into colostrum (${\text{TE}}_{\mathrm{C}:\mathrm{S}}$) and breast milk (${\text{TE}}_{\mathrm{B}:\mathrm{S}}$), stratified by exposure group.

Exposure categorya	$N$	Transfer efficiency [median (IQR)]
		PFOA	PFNA	PFHxS	PFOS
${\text{TE}}_{\mathrm{C}:\mathrm{S}}$
Background	13	2.94 (2–3.77)	2.58 (1.78–3.1)	1.86 (1.31–2.36)	0.66 (0.4–0.92)
Intermediate	56	2.74 (1.99–3.82)	2.60 (1.81–3.74)	1.33 (0.85–1.87)	0.76 (0.61–1.09)
High	16	2.83 (2.57–3.65)	2.63 (2.03–3.64)	1.81 (1.23–2.27)	1.13 (0.92–1.26)
${\text{TE}}_{\mathrm{B}:\mathrm{S}}$
Background	21	2.25 (1.82–3.45)	3.03 (2.27–3.57)	1.86 (1.39–2.36)	0.99 (0.78–1.2)
Intermediate	68	2.18 (1.72–2.96)	2.63 (2.09–3.98)	1.12 (0.79–1.36)	1.00 (0.83–1.2)
High	20	1.98 (1.7–2.51)	1.94 (1.57–2.89)	1.41 (1.14–1.54)	1.09 (1–1.19)

Note: Samples $<\text{LOQ}$ were included and substituted with the LOQ divided by the square root of 2 when a measured concentration was not available. B, breast milk; C, colostrum; IQR, interquartile range; LOQ, limit of quantification; PFHxS, perfluorohexane sulfonic acid; PFNA, perfluorononanoic acid; PFOA, perfluorooctanoic acid; PFOS, perfluorooctane sulfonic acid; S, serum; TE, transfer efficiency.

^a Exposure levels were categorized based on maternal serum PFHxS concentrations (${\mathrm{C}}_{\text{PFHxS}}$, ng/mL) at delivery. Background: ${\mathrm{C}}_{\text{PFHxS}}\le 0.78$. Intermediate: $0.78<{\mathrm{C}}_{\text{PFHxS}}\le 36$. High: $36<{\mathrm{C}}_{\text{PFHxS}}$.