Background An excessive rise in maternal lipids during pregnancy may have detrimental impacts on maternal and fetal health leading to adverse pregnancy outcomes. However, knowledge gaps exist with respect to the association between lipid biomarkers and birth outcomes. Methods We conducted a secondary data analysis of healthy pregnant women ( N = 25) with mid-pregnancy fasting serum samples collected at 22–28 weeks of gestation and birth outcome data. Serum was analyzed for conventional lipid profile (total-C, HDL-C, LDL-C, and triglycerides) and lipoprotein subclass distribution, including particle number (nM) and size (nm), for very low-density lipoprotein (VLDL)/chylomicron (CM), low density lipoprotein (LDL), and high-density lipoprotein (HDL), by nuclear magnetic resonance spectroscopy. Associations between maternal lipids and birth outcomes, including birth weight (g) and gestational age (weeks), were assessed using multivariable linear regression, adjusted for pre-pregnancy BMI. Results Although conventional lipids were not associated ( p > 0.05) with birth outcomes, every 1-unit increment in large VLDL/CM particles (nM) and VLDL/CM size (nm) was associated with an increase in birth weight (confounder-adjusted β-coefficient, 45.80 g [5.30, 86.20, p = 0.003] and 24.90 g [8.80, 40.90, p = 0.002], respectively). Among the HDL subclass parameters, a 1-unit (nM) increase in the concentration of total HDL-particles was associated with a reduced birth weight (confounder adjusted β-coefficient, -19.40 g [95% confidence interval, -36.70, -2.20]; p = 0.03) after adjustment for maternal pre-pregnancy BMI. Conclusion The preliminary results of this pilot study suggest that total particle concentrations of VLDL/CM and HDL in mid-pregnancy have divergent associations with birth weight, potentially reflecting the specific roles of these lipoprotein particles with respect to placental function and fetal growth.