It is unclear if the benefits of antenatal corticosteroids (ACS) in reducing neonatal respiratory morbidity are outweighed by the risks of maternal hyperglycaemia and neonatal hypoglycaemia in women with diabetes or babies born via a late preterm or early term planned caesarean section (CS). This study aimed to characterise the pattern of maternal and neonatal glycaemic response in women with pregestational, or gestational diabetes administered ACS or placebo prior to a planned, pre-labour CS between 35+0 and 38+6 weeks gestation. Participants from the PRECeDe pilot (ACTRN12619001475134) were randomised to receive either two injections of betamethasone (11.4 mg) or normal saline placebo, 24 hours apart within 7 days of planned CS. Glycaemic data from 47 women (22 ACS, 25 placebo) and 51 neonates (24 ACS, 27 placebo) were analysed. The primary outcome measure was the peak, nadir and time to peak maternal blood glucose levels (BGLs). ACS resulted in higher mean antenatal BGLs (7.3 vs 5.5 mmol/L) with a peak at approximately 9 hours and 36 hours following the first dose. The ACS-exposed group had significantly higher antenatal fasting, pre-prandial and post-prandial BGLs with a greater proportion of above target fasting and post-prandial BGLs (p<0.001). Postnatal hyperglycaemia was common following ACS (18% vs 12%), while neonatal hypoglycaemia was less frequent (38% vs 48%). Maternal hyperglycaemia is associated with ACS administration in women with diabetes requiring careful monitoring and insulin titration. Larger trials are required to investigate the relationship between maternal hyperglycaemia and neonatal hypoglycaemia.