Introduction:Several studies have shown that women with pre-existing diabetes mellitus have significantly lower pregnancy-associated plasma protein-A levels than those without. This study aimed to evaluate whether first-trimester pregnancyassociated plasma protein-A multiple of median is associated with gestational diabetes mellitus in Chinese pregnant women. Methods:This prospectively collected case series was conducted in a regional hospital in Hong Kong. All consecutive Chinese women with a singleton pregnancy who attended the hospital for their first antenatal visit (before 14 weeks' gestation) from April to July 2014 were included. Pregnancyassociated plasma protein-A multiple of median was compared between the gestational diabetic (especially for early-onset gestational diabetes) and non-diabetic groups. The correlation between pregnancy-associated plasma protein-A level and glycosylated haemoglobin level in women with gestational diabetes was also examined. Results:Of the 520 women recruited, gestational diabetes was diagnosed in 169 (32.5%). Among them, 43 (25.4%) had an early diagnosis, and 167 (98.8%) with the disease were managed by diet alone. The gestational diabetic group did not differ significantly to the non-diabetic group in pregnancyassociated plasma protein-A (0.97 vs 0.99, P=0.40) or free β-human chorionic gonadotrophin multiple of median (1.05 vs 1.02, P=0.29). Compared with the non-gestational diabetic group, women with early diagnosis of gestational diabetes had a non- Association between pregnancy-associated plasma protein-A levels in the first trimester and gestational diabetes mellitus in Chinese womenNew knowledge added by this study • This is the first study to assess the association of first-trimester pregnancy-associated plasma protein-A multiple of median (PAPP-A MoM) with gestational diabetes mellitus (GDM) in a Chinese population. PAPP-A MoM was not predictive of development of non-insulin-dependent GDM in Chinese women.• There was no correlation between PAPP-A MoM and glycosylated haemoglobin level in Chinese women with GDM. PAPP-A levels were not useful to predict and identify poor glycaemic control in women with GDM.• There was a high prevalence of GDM (32.5%) in the Chinese population. Implications for clinical practice or policy • PAPP-A and β-human chorionic gonadotrophin do not seem to be predictive of non-insulin-dependent GDM.Other predictive model that comprises the maternal and clinical risk factors in Chinese women is warranted to identify women at risk of GDM.• Further studies that employ the new diagnostic criteria for GDM are warranted to examine the potential of first-trimester biochemical markers to predict GDM as well as their influence on the prevalence of GDM in the Chinese population.

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