Maternal and neonatal outcomes of pregnancy-associated cancer by cancer type

Pregnancy-associated cancer (PAC) is diagnosed in approximately 1 in 1,000 pregnancies, and its incidence is rising with delayed childbearing. While previous meta-analyses have established overall PAC-associated risks, the extent to which maternal and neonatal outcomes differ by cancer type remains poorly characterised. We conducted an updated systematic review following PRISMA 2020 guidelines. MEDLINE, Embase, Web of Science, Cochrane Library, and Scopus were searched from inception to June 2026. We included observational studies (cohort, case-control, population-based registries) reporting maternal and neonatal outcomes stratified by cancer type. Systematic reviews were used for reference checking only and were not included as primary evidence sources. Study-level risk of bias was assessed using the Newcastle-Ottawa Scale, and certainty of evidence was evaluated using GRADE. Random-effects meta-analyses were performed for overall outcomes, with narrative synthesis for cancer-specific analyses. The review was not prospectively registered; this is acknowledged as a limitation. Primary studies (70,097,167 births, 59,190 PAC cases) were included. Women with PAC had significantly increased risks of preterm birth (RR 3.07, 95% CI 2.37–3.98; prediction interval 0.93–10.14; 16 studies; I² = 98%), venous thromboembolism (RR 6.76, 95% CI 5.08–8.99; 6 studies; I² = 0%), maternal death (RR 41.58, 95% CI 20.38–84.83; 3 studies; I² = 44%), and caesarean section (RR 1.58, 95% CI 1.31–1.89; 13 studies; I² = 98%). Neonatal risks included low birth weight (RR 1.84, 95% CI 1.69–2.01; 11 studies; I² = 95%) and low Apgar score (RR 1.36, 95% CI 1.20–1.56; 6 studies; I² = 0%). Among malignancy types with available data, colorectal, breast, and cervical cancers demonstrated higher reported risks of adverse outcomes within individual studies; however, direct comparisons between cancer types are not supported by the available evidence. The majority of preterm births were iatrogenic (up to 88% in the INCIP cohort). Chemotherapy after the first trimester was not associated with increased congenital malformations but was associated with lower birth weight. Pregnancy-associated cancer substantially increases maternal and neonatal morbidity and mortality. The strongest evidence concerns overall PAC-associated outcomes. Cancer-type-specific evidence is based on narrative synthesis of within-study associations and should be considered exploratory. Multidisciplinary management, careful delivery timing, and thromboprophylaxis are important considerations, though clinical recommendations should be individualised. These findings should be interpreted cautiously given the observational nature of the evidence, substantial heterogeneity for some outcomes, and the absence of formal comparative analyses between cancer types.