BackgroundPregnant women with pre-existing diabetes (Type 1 or Type 2) have increased rates of adverse maternal and neonatal outcomes. Current clinical guidelines support elective birth, at or near term, because of increased perinatalmortality during the third trimester of pregnancy.This review replaces a review previously published in 2001 that included "diabetic pregnant women", which has now been split into two reviews. This current review focuses on pregnant women with pre-existing diabetes (Type 1 or Type 2) and a sister review focuses on women with gestational diabetes.ObjectivesTo assess the effect of planned birth (either by induction of labour or caesarean birth) at or near term gestation (37 to 40 weeks' gestation) compared with an expectant approach, for improving health outcomes for pregnant women with pre-existing diabetes and their infants. The primary outcomes relate to maternal and perinatal mortality and morbidity.Search methodsWe searched Cochrane Pregnancy and Childbirth's Trials Register, ClinicalTrials. gov, the WHO International Clinical Trials Registry Platform (ICTRP) (15 August 2017), and reference lists of retrieved studies.Selection criteriaWe planned to include randomised trials (including those using a cluster-randomised design) and non-randomised trials (e.g. quasirandomised trials using alternate allocation) which compared planned birth, at or near term, with an expectant approach for pregnant women with pre-existing diabetes.Data collection and analysisTwo of the review authors independently assessed study eligibility. In future updates of this review, at least two of the review authors will extract data and assess the risk of bias in included studies. We will also assess the quality of the evidence using the GRADE approach.Main resultsWe identified no eligible published trials for inclusion in this review. We did identify one randomised trial which examined whether expectant management reduced the incidence of caesarean birth in uncomplicated pregnancies of women with gestational diabetes (requiring insulin) and with pre-existing diabetes. However, published data from this trial does not differentiate between pre-existing and gestational diabetes, and therefore we excluded this trial.Authors' conclusionsIn the absence of evidence, we are unable to reach any conclusions about the health outcomes associated with planned birth, at or near term, compared with an expectant approach for pregnant women with pre-existing diabetes.This review demonstrates the urgent need for high-quality trials evaluating the effectiveness of planned birth at or near term gestation for pregnant women with pre-existing (Type 1 or Type 2) diabetes compared with an expectant approach.