We examined the association between pregnancy and life course lipid trajectories. Linked data from the Norwegian HUNT Study and the Medical Birth Registry of Norway yielded 19,987 parous and 1,625 nulliparous women. Using mixed effects spline models, we estimated differences in non-fasting lipid levels from before to after first birth in parous women and between parous and nulliparous women. High density lipoprotein cholesterol (HDL-C) dropped by -4.2 mg/dL (95% CI: -5.0, -3.3) from before to after first birth in adjusted models, a 7% change, and total cholesterol to HDL-C ratio (TC/HDL-C) increased by 0.18 (95% CI: 0.11, 0.25) with no change in non-HDL-C or triglycerides. Changes in HDL-C and TC/HDL-C associated with pregnancy persisted for decades, leading to altered life course lipid trajectories. For example, parous women had a lower HDL-C than nulliparous women at age 50 (-1.4 mg/dL, 95% CI: -2.3, -0.4). Adverse changes in lipids were greatest following first birth with small changes after subsequent births and were larger in women who did not breastfeed. Findings suggest that pregnancy is associated with long-lasting adverse changes in HDL-C, potentially setting parous women on a more atherogenic trajectory than prior to pregnancy.