Gestational diabetes mellitus (GDM) could have a variable degree of adverse effects on pregnancy outcomes for both pregnant women and newborns. The purpose of the study was to explore the effect of GDM on pregnancy outcomes in advanced primiparous women. A total of 1076 advanced primiparous women were included between January 2020 and December 2022. All these women were divided into the GDM group (n = 434) and the non-GDM group (n = 642). Variables included baseline characteristics, maternal, and newborn outcomes were collected. The risk of each adverse outcome was analyzed by multivariate logistic regression models. The effect of blood glucose control on pregnancy outcomes was further analyzed among GDM women with good glycaemic control (n = 381) and poor glycaemic control (n = 53). Analysis of baseline characteristics demonstrated a significant difference in prepregnancy body mass index (median, IQR: 22.27 [20.58–24.44] vs 21.17 [19.53–22.86], P < .01) between the GDM group and the non-GDM group. A significantly higher incidence rate of adverse pregnancy outcomes was found in advanced primiparous women with GDM, such as polyhydramniosis, premature birth, low-birth weight, macrosomia, and neonatal intensive care unit admission (all P < .05). Compared with the non-GDM group, the risk of polyhydramniosis was nearly twice as high in the GDM group (adjusted odds ratio: 1.94, 95% confidence interval: 1.01–3.72, P = .04) after adjusted baseline characteristics. Among the GDM group, the women with poor glycaemic control showed a significantly higher incidence rate of polyhydramnios, hypertensive disorders of pregnancy, cesarean delivery, premature birth, low-birth weight, macrosomia, and neonatal intensive care unit admission was significant than the women with good glycaemic control (all P < .05). GDM was an independent risk factor for polyhydramnios in advanced primiparous women. At the same time, good glycaemic control in diabetics advanced primiparous women could reduce adverse pregnancy outcomes.