Perinatal outcomes following bariatric surgery between a first and second pregnancy: a population data linkage study I Ibiebele, a,b F Gallimore, a,c M Schnitzler, a,d S Torvaldsen, a,e JB Ford a,b a Women and Babies Research, The University of Sydney Northern Clinical School, St Leonards, New South Wales, Australia b Northern Sydney Local Health District, Kolling Institute, St Leonards, New South Wales, Australia c North Shore Private Hospital, St Leonards, New South Wales, Australia d Department of Colorectal Surgery, Royal North Shore Hospital, St Leonards, New South Wales, Australia e School of Public Health and Community Medicine, University of New South Wales, Kensington, New South Wales, Australia Correspondence: I Ibiebele, Clinical and Population Perinatal Health Research, Douglas Building, Royal North Shore Hospital, St Leonards, NSW 2065, Australia. Email: Ibinabo.ibiebele@sydney.edu.au Accepted 11 October 2019. Published Online 20 November 2019. Objectives To describe the population of women having bariatric surgery and compare the pregnancy outcomes for women having bariatric surgery with a non-bariatric surgery population having a first and second pregnancy. Design Population-based record linkage study. Setting New South Wales (NSW), Australia. Population All women aged 15–45 years with a hospital record in NSW (2002–2014) and all women giving birth in NSW (1994– 2015; n = 1 606 737 women). Methods Pregnancy and birth outcomes were compared between first and second pregnancies using repeated-measures logistic regression and paired Student’s t-tests. Bariatric and non-bariatric groups were also compared. Main outcome measures Maternal diabetes, preterm birth (<37 weeks of gestation) and large for gestational age. Results There was a 13-fold increase in hospitalisations for primary bariatric surgery during 2002–2014. Compared with the general birthing population, women who had bariatric surgery experienced higher rates of hypertension, diabetes, and preterm birth. Among women who had bariatric surgery between a first and second pregnancy, there were reduced rates of hypertension (OR 0.39, 95% CI 0.29–0.53), spontaneous preterm birth (OR 0.37, 95% CI 0.16–0.86), infants that were large for gestational age (OR 0.63, 95% CI 0.44–0.88), and the admission of infants to a special care nursery or neonatal intensive care (OR 0.64, 95% CI 0.46–0.90) in the second pregnancy. Rates for small-for-gestational age and gestational diabetes following surgery were 8.3 and 11.4%, respectively Conclusions Bariatric surgery between a first and second pregnancy was associated with reductions in obesity-related adverse pregnancy outcomes. Bariatric surgery performed for the management of obesity in accordance with current clinical criteria is associated with improved pregnancy outcomes in a subsequent pregnancy. Keywords Bariatric surgery, diabetes, pregnancy, preterm birth. Tweetable abstract Bariatric surgery for obesity may improve pregnancy and birth outcomes in a subsequent pregnancy. Please cite this paper as: Ibiebele I, Gallimore F, Schnitzler M, Torvaldsen S, Ford JB. Perinatal outcomes following bariatric surgery between a first and second pregnancy: a population data linkage study. BJOG 2020;127:345–354. Introduction Obesity is a major risk factor for heart disease, stroke, osteoarthritis, and some cancers. 1 The rate of obesity is increasing worldwide, having tripled between 1975 and 2016. 1 Obesity rates among women of reproductive age have mirrored rates among the general population. Between 1995 and 2008, rates increased 73% (from 8.6 to 14.9%) among Australian women aged 18–24 years, increased 23% (from 15.0 to 18.4%) among women aged 25–34 years, and increased 42% (from 16.1 to 22.9%) among women aged 35– 44 years. 2 Obesity among women of reproductive age is asso- ciated with subfertility, recurrent miscarriage, gestational diabetes (GDM), and fetal growth restriction, as well as car- diovascular disease and diabetes in later life. 3 Maternal obe- sity is a risk factor for elective and emergency caesarean section, 4 and infants born to mothers who are obese are at increased risk of neonatal morbidity and childhood obesity. 3 345 ª 2019 Royal College of Obstetricians and Gynaecologists DOI: 10.1111/1471-0528.15993 www.bjog.org Epidemiology