Data source and study population
Births were identified from the records collected by the information system of Guangdong Women and Children Hospital from September 2014 to March 2018 (N = 37,193). We extracted maternal information including age at delivery, delivery mode, pre-pregnancy weight and height, parity, the date of last menstrual period, delivery date as well as smoking status during pregnancy. We also extracted the information of the newborns including birth weight and infant sex. The test results of maternal mid-pregnancy ApoA-1, ApoB and oral glucose tolerance test (OGTT) were obtained from laboratory information system of the study hospital. Maternal mid-pregnancy ApoA-1 and ApoB values were determined based on fasting blood samples tested during their routine pregnancy tests at a median of 18 weeks of gestation (IQR : 16 - 22 weeks) and were measured by immunoturbidimetric assays.
The women satisfying the follow criteria were included in the analysis: 1) who had the data of mid-pregnancy ApoA-1 and ApoB, OGTT, the date of last menstrual period, pre-pregnancy weight and height; 2) gave a single live birth. We excluded post-term births (gestational age>42 weeks), babies with birth defects or the recorded birthweight out of the range 500-5000 g. We further excluded the outlier value (< 25th -1.5 IQR or > 75th +1.5 IQR) of ApoA-1 and ApoB. Finally, a total of 5,986 mother-newborn pairs were included in the present study (Fig. 1) . We compared characteristics between included women (n= 5,986) and those who were excluded due to mid-pregnancy apolipoprotein measurements were not available (n= 7,917). Mothers in the included group were slightly younger (32.2 vs 32.4; p = 0.021) than women who were excluded but there was no significant difference in pre-pregnancy BMI or the incidence of preterm birth between this two groups (see supplementary Table S1 ).
As all data used in the present study was de-identified, no written informed consents were obtained from the participants. The study protocol has been approved by the ethics committee of Guangdong Women and Children Hospital.