There are few data on pregnancy outcomes in women with pre‐diabetes (HbA1c 41–49 mmol/mmol) at pregnancy booking. We aimed to (i) identify the proportion of women in Counties Manukau Health (CMH), South Auckland, New Zealand (NZ), with pre‐diabetes at booking and (ii) compare outcomes between women with normal HbA1c and pre‐diabetes.

Materials and methods
Using data from a multi‐ethnic population of 10,869 singleton pregnancies, booked at <20 weeks from January 2017 to December 2018 in CMH, we compared outcomes between those with normal HbA1c (≤40 mmol/mol) and those with pre‐diabetes (HbA1c 41–49 mmol/mol). The primary outcomes were gestational diabetes mellitus (GDM) by NZ criteria and large for gestational age (LGA) defined as birthweight >90th customised centile. Logistic regression determined the contribution of HbA1c 41–49 mmol/mol to the development of GDM.

Among 10,869 participants, 193 (1.78%) had an HbA1c 41–49 mmol/mol at <20 weeks’ gestation. Those with HbA1c 41–49 mmol/mol were 11 times more likely to develop GDM (59.6 vs 7.9%; adjusted odds ratio (aOR) 11.16 (7.59, 16.41)) and were more likely to have an LGA baby (47 (24.4%) vs 1436 (13.5%) aOR 1.63 (1.10, 2.41)) versus those with normal HbA1c. They also had significantly higher rates of pre‐eclampsia, caesarean sections, preterm births and perinatal deaths. Conclusions: Nearly two‐thirds of women with a booking HbA1c of 41–49 mmol/mmol developed GDM as well as multiple other perinatal complications compared to women with HbA1c ≤40. Trials to evaluate the impact of treatment in early pregnancy on the risk of late‐pregnancy complications are required.