Background: Women with intellectual disability experience significant health inequalities across the lifespan but evidence on their maternity care and perinatal outcomes is limited. Methods: We conducted a retrospective matched cohort study using linked electronic health records from the Early Life Cross Linkage in Research, Born in South London (eLIXIR-BiSL) network. Women with intellectual disability were identified in primary care and secondary mental healthcare. We matched 91 pregnancies in women with intellectual disability (mean maternal age 29·9 years) to 357 pregnancies in women without intellectual disability, on maternal age, parity, and calendar year between 2018 and 2023. We assessed whether intellectual disability was recorded in maternity records and compared socio-demographic and clinical characteristics and perinatal outcomes between groups using logistic regression. Findings: Intellectual disability was recorded in the maternity records for only 56.0% women with intellectual disability recorded in their primary care or secondary mental healthcare records. Recording was not associated with maternal characteristics and appeared to improve over time. Compared with women without intellectual disability, women with intellectual disability had higher levels of health-related risk factors and indicators of social vulnerability, including current smoking, mental health conditions, multimorbidity, socioeconomic deprivation, domestic abuse, and social services involvement. Their babies had lower mean birth weight than babies born to women without intellectual disability (2992g vs 3306g, p<0·001) and were more likely to be born preterm (21.4% vs 5·9%, p<0.001). In adjusted models, maternal intellectual disability remained associated with preterm birth (OR 3·09, 95%CI 1·34–7·16). Interpretation: Women with intellectual disability are more likely to have obstetric risk factors and to experience adverse birth outcomes. Intellectual disability was frequently absent from maternity records, potentially limiting recognition of women’s support needs and implementation of reasonable adjustments in maternity care.