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Background Diagnosis of a hereditary cancer syndrome may impact family planning, particularly in reproductive age individuals. Factors influencing reproductive decision-making are understudied in individuals with germline CDH1 pathogenic or likely pathogenic (P/LP) variants.Methods We characterised reproductive decision-making and perinatal outcomes in 121 individuals aged 18–49 with hereditary diffuse gastric and lobular breast cancer syndrome due to a germline CDH1 P/LP variant.Results Half of individuals (50%, 60/121) reported their CDH1 diagnosis impacted family planning. Psychosocial and economic barriers to reproduction were encountered by 47% (56/119) of patients. Additionally, 12% (15/121) of individuals delayed pregnancy to prioritise personal cancer risk management with either endoscopic surveillance, prophylactic total gastrectomy (PTG) or mastectomy. Women were more likely to experience guilt about passing their CDH1 variant to offspring compared with men. Perinatal and fetal outcomes were investigated in six women who gave birth at a median time of 24 months (IQR 20–44) after PTG. Maternal micronutrient deficiencies were not uncommon in pregnant women after PTG despite compliance with a bariatric, prenatal multivitamin. Majority of women who became pregnant after PTG reported worsening post-gastrectomy syndromes. Most infants (90%, 9/10) born after PTG were full-term and no fetal complications were reported.Conclusion Reproductive decision-making is complex in individuals with germline CDH1 variants, who often encounter psychosocial and physical challenges during family planning and pregnancy. However, successful pregnancy is possible after PTG with the guidance of a multidisciplinary team including maternal fetal medicine specialists and a registered dietitian.Trial registration number NCT03030404.