['To investigate the clinical significance of falling insulin requirements in women with preexisting or overt diabetes in pregnancy.', 'A retrospective review of 139 pregnancies was conducted in women, with preexisting diabetes, delivering between January 2010 and January 2013. Women with falling insulin requirements of 15% or more from the peak total daily dose in late pregnancy were considered case subjects (n = 35). The primary outcome consisted of a composite of clinical markers of placental dysfunction, including preeclampsia, small for gestational age (SGA, ≤5th percentile for gestational age), stillbirth (>20 weeks), and premature delivery (≤30 weeks).', 'A total of 25.2% of women had >15% fall in insulin requirements with nulliparity as the only predictor at baseline (odds ratio [OR] 2.5 [95% CI 1.1-5.7], P = 0.03). Falling insulin requirements were associated with an increased risk of preeclampsia (OR 3.5 [1.1-10.7], P < 0.05) and the composite of clinical markers of placental dysfunction (4.4 [1.73-11.26], P = 0.002). Although falling insulin requirements were associated with higher rates of SGA (3.4 [1.0-11.3], P = 0.048), they were not associated with other adverse neonatal outcomes. However, there was a higher incidence of neonatal intensive care unit admission (15.5 [3.1-77.6], P = 0.001) and earlier delivery in this group (median 37.7 weeks [IQR 34.3-38.4] vs. 38.3 weeks [37.4-38.9], P = 0.014).'] Are falling insulin requirements associated with adverse obstetric outcomes in women with preexisting diabetes?