We retrieved 13,112 studies from Chinese and English databases conducted before August 2023, and 9,489 studies were obtained by removing duplicate studies through Endnote and manual methods. After title and abstract screening, 189 studies were included. After rescreening by reading the full text, 32 studies that reported both the incidence and factors influencing DOL and 3 studies that reported only the incidence were ultimately included. No new studies were found after reviewing the references of the included studies and related reviews. The study screening process is shown in Fig. 1.

PRISMA flowchart for the identification of studies

A total of 35 included studies were conducted from 1999 to 2023 in 8 countries, including China (n = 23), the United States of America (USA, n = 6), Canada (n = 1), Peru (n = 1), India (n = 1), Australia (n = 1), Brazil (n = 1), and Ghana (n = 1). A total of 19,176 women were included in these studies, 4,922 of whom had DOL. The methods of follow-up involved medical records, questionnaires, or interviews. The mean NOS score of all the studies was ≥ 6 points, indicating that these studies had good methodological quality. The general characteristics and NOS scores of the included studies, sorted alphabetically by author name, are summarized in Table 1.

The combined incidence of DOL was obtained via meta-analysis. The meta-analysis results of factors influencing DOL are summarized in Table 2 according to the order of reporting. Combined with the qualitative description of the influencing factors, all the influencing factors involved could be divided into three categories: maternal-related factors, infant-related factors, and breastfeeding-related factors.

A random-effects model was used to assess the incidence of DOL in 35 studies, and the result was 30% (95% CI 26, 34) (Fig. 2). Subgroup analysis by country category, combined with at least two or more studies, revealed an incidence of DOL of 30% in China (95% CI 26, 35) and 34% in the USA (95% CI 24, 43). The incidence of DOL in the USA was slightly higher than that in China (Fig. 3).

Forest plot of DOL incidence

Forest plot of the subgroup analysis of DOL incidence

There was a statistically significant difference in age [5, 26, 28, 33] between the DOL and non-DOL groups (WMD =-0.30; 95% CI -0.573, -0.40), but the sensitivity analysis result was not robust. The combined results of 9 studies [24, 31, 36, 41,42,43, 45, 46, 48] and 5 studies [4, 20, 30, 40, 49], respectively, could not determine the association between a maternal age ≥ 35 years (RR = 1.40; 95% CI 0.96, 2.04) and ≥ 30 years (RR = 1.33; 95% CI 0.98, 1.80) and DOL.

The pooled results of 8 studies [20, 21, 23, 24, 37, 40, 45, 48] and 3 studies [27, 29, 46], respectively, revealed that a prepregnancy BMI ≥ 25.0 kg/m2 (RR = 1.47; 95% CI 1.17, 1.84) and a prepregnancy BMI ≥ 24.0 kg/m2 (RR = 1.41; 95% CI: 1.14, 1.74) were risk factors for DOL. However, the correlation between prepregnancy BMI [26, 30, 33] (WMD = 1.26; 95% CI -1.22, 3.75) and DOL was uncertain. Excessive gestational weight gain (GWG) [24, 37, 40, 41, 45, 46, 48] (RR = 1.38; 95% CI 1.07, 1.77) was a risk factor for DOL, but the sensitivity analysis result was not robust.

The combined results of 14 [20, 21, 24, 26, 28,29,30, 33, 36,37,38, 41, 45, 48], 13 [5, 20, 21, 27,28,29,30, 36,37,38, 41, 42, 45], 6 [21, 29, 35, 38, 41, 47] and 2 [5, 29] studies, respectively, revealed that gestational diabetes mellitus (GDM) (RR = 1.32; 95% CI 1.18, 1.49), hypertensive disorders of pregnancy (HDP) (RR = 1.66; 95% CI 1.30, 2.12), thyroid disease during pregnancy (RR = 1.18; 95% CI 1.05, 1.32), and a serum albumin level < 35 g/L (RR = 1.57; 95% CI 1.12, 2.20) were risk factors for DOL. The descriptive analysis could not determine whether anaemia [21, 29, 38] was associated with DOL, and there might be no association between ovarian cysts during pregnancy [21, 29] and DOL.

The pooled results of 23 studies [5, 19,20,21,22,23, 25,26,27,28,29, 31, 33, 35, 36, 38,39,40,41, 43, 44, 46, 48] revealed that primiparity (RR = 1.40; 95% CI 1.25, 1.56) was a risk factor for DOL. The combined results of 20 [4, 5, 24, 26, 28, 30,31,32,33, 35,36,37,38, 40, 41, 44,45,46,