Easy voc syringe

Breath sampling was performed at 3 months after childbirth (follow-up visit 4) following the protocol described by Sola Martínez et al.^{40 (link)}. Briefly, exhaled breath was collected in 1 L Tedlar gas sampling bags. Specifically, mixed breath sample (alveolar and dead space) were collected. Then, the exhaled breath contained in the gas sampling bags was immediately transferred to to thermal desorption tubes (Tenax TA, Markes International) to avoid the diffusion through the bag wall. A room air content sample was also collected directly through Tenax tube for each exhaled breath sample using an Easy-VOC syringe (Markes International) to control for environmental conditions at sampling. Almost all samples were analysed on the same day of collection, being a maximum storage period of less than one week. The Tenax tubes were stored at 4 °C for storage periods longer than one day. Tenax tubes were heated to 335ºC for 25 min for reconditioning after each use. The Tedlar bags were cleaned with 10 nitrogen flushes (99.9% nitrogen purity) before use. Thus, the levels of background artefacts (N,N-dimethylacetamide and phenol) in the gas sampling bags were strongly reduced (Supplementary Fig. S12).