Introduction There is international concern over rising rates of CS and its impacts on maternal and neonatal health outcomes. Of interest are the factors driving the increase in primary caesareans in a 2nd birth. Objectives To examine effects of previous birth factors on subsequent planned CS. Methods Women with both 1st and 2nd births were identified from NSW birth data from 2000-2009. The study population included only women with VB at 1st birth and excluded those who had an indisputable indication for CS in the 2nd birth (multiple pregnancy, breech presentation or placenta praevia). Logistic regression was used for the analysis. Results Of the 114,287 women, 4,787 (4.2%) had planned CS at 2nd birth. After adjusting for 2nd pregnancy risk factors including interval between two births, year at birth, maternal age, hospital location, private care, hypertension, diabetes, infant size and antepartum hemorrhage, independent 1st birth risk factors for planned CS (in order of effect size) were 3rd-4th degree tear, severe neonatal morbidity, a perinatal death, severe maternal morbidity, instrumental birth, large infant, labour induction, epidural, use of oxytocics and episiotomy. The leading four 1st birth risk factors increased the risk of planned CS by more than 100%, for example odds ratio of 3rd-4th degree tear: 5.00 (95% CI 4.58-5.44). Conclusion Women who had obstetric interventions and adverse pregnancy outcomes in the first birth were at increased risk of planned CS in the second birth. The results indicate the importance of ‘getting the first birth right’ in reducing CS rate.Australian National Health and Medical Research Council (NHMRC) Capacity Building Grant (#573122
