OBJECTIVE:The aim was to investigate birth characteristics, obstetric and neonatal outcomes of the first childbirth in women with Marfan syndrome by use of Swedish national registers since pregnancy-related outcomes in women with Marfan syndrome have only been sparsely investigated. STUDY DESIGN:In this national population-based cohort study and matched case-control study of Swedish women born 1973-1993, women with Marfan syndrome (n=273) were compared to women without the condition (n=1 017 265). The study population was followed until 2013. A total of 364 553 mother-firstborn-offspring pairs were analyzed. Sixty-one women with Marfan syndrome became mothers. Women with Marfan syndrome were also compared to 543 healthy controls. RESULTS:Women with Marfan syndrome were more often born preterm (p<0.001), small-for-gestational age (p<0.001), and delivered by cesarean section (p=0.001). Women with Marfan syndrome had no increased risk of giving birth by cesarean section (p=0.079). No increased neonatal risks in their children were found. Women with Marfan syndrome were less likely to give birth than those without (p<0.001). There were no maternal deaths. CONCLUSIONS:Women with Marfan syndrome were more likely to be born preterm, SGA and by cesarean section. These increased risks of preterm birth and SGA babies were not found in connection with their own first childbirth. Pregnancies with known fetal Marfan syndrome have to be carefully monitored. The results are important for obstetricians giving preconception counseling and treating women with Marfan syndrome. Further studies are needed to evaluate risks during pregnancy and long-term effects of pregnancy on the cardiovascular status of women with Marfan syndrome.