Recommended reference values for serum lipids during early and middle pregnancy: a retrospective study from China

BACKGROUND: Disturbances in maternal lipid metabolism have been shown to increase the risk of adverse pregnancy outcomes. However, there is no consensus as to what constitutes normal maternal lipid values during pregnancy. Thus, the aim of this study was to establish serum lipid reference ranges during early and middle pregnancy. METHODS: We conducted a retrospective survey in Beijing from 2013 to 2014. A total of 17,610 singleton pregnancies with lipid data from early and middle pregnancy were included. First, after excluding women with adverse pregnancy outcomes, we performed a descriptive analysis of total cholesterol (TC), triglycerides (TG), high-density lipid cholesterol (HDL-C) and low-density lipid cholesterol (LDL-C) levels using means and standard deviations to determine appropriate percentiles. Second, in the total population, we examined the lipid levels in different trimesters with the risk of adverse pregnancy outcomes using categorical analyses and logistic regression models. Third, we determined the lipid reference range in early and middle pregnancy based on the first two results. Finally, based on the reference ranges we determined, we assessed whether the number of abnormal lipid values affected the risk of adverse pregnancy outcomes. RESULTS: (1) Serum levels of TC, TG, LDL-C and HDL-C all increased significantly from early to middle pregnancy, with the greatest increase in TG. (2) A trend towards an increasing incidence of adverse pregnancy outcomes was observed with increasing levels of TC, TG, and LDL-C and decreasing levels of HDL-C in both early and middle pregnancy. (3) We recommend that serum TC, TG and LDL-C reference values in early and middle pregnancy should be less than the 95th percentiles, whereas that of HDL-C should be greater than the 5th percentile, i.e., in early pregnancy, TC < 5.64 mmol/L, TG < 1.95 mmol/L, HDL-C > 1.23 mmol/L, and LDL-C < 3.27 mmol/L, and in middle pregnancy, TC < 7.50 mmol/L, TG < 3.56 mmol/L, HDL-C > 1.41 mmol/L, and LDL-C < 4.83 mmol/L. (4) Higher numbers out-of-range lipids during early and middle pregnancy were correlated with a higher risk of adverse pregnancy outcomes. CONCLUSIONS: The reference ranges recommended in this paper can identify pregnant women with unfavourable lipid values.