Table 1.

Inclusion and exclusion criteria according to time of inclusion

	Before surgery (T1)	After surgery (T2-T5)	Pregnancy (T6)	Breast milk composition
Inclusion criteria	*women aged 18–45 *approved for bariatric surgery (all types of surgery) *internet connection and email	*women aged 18–45 *previous bariatric surgery (all types of surgery) *internet connection and email	*women aged 18–45 *previous bariatric surgery (all types of surgery) * < 15 weeks of gestation *internet connection and email	*women aged 18–45 *lactating women with previous bariatric surgery *pregnancy duration between 37 and 41 weeks
Exclusion criteria	*infertility (e.g. menopause, hysterectomy)	*infertility (e.g. menopause, hysterectomy)	/	*use of medication possibly affecting breast milk (discussed individually with neonatologist) *problems or difficulties with breastfeeding * > 10 % weight loss in newborn 4 days after delivery *diabetes or GDM

Abbreviations: GDM gestational diabetes mellitus, T time = measuring moment