Objective: We sought to investigate the changes in circulating serum lipids and lipoproteins, including lipoprotein (a), and low-density lipoprotein size in women during normal pregnancy. Study Design: Twenty-two women (mean age, 31 ± 5 years; 13 primiparous subjects) were studied during uncomplicated pregnancy with normal outcome. Twenty-four nulliparous women of similar age (31 ± 4 years) were studied as control subjects. Results: Serum triglycerides and total and low-density lipoprotein cholesterol increased significantly during pregnancy in all women. Women with changes in low-density lipoprotein during the second and third trimesters showed a more marked increase in serum triglycerides, and this effect was slightly more evident in the multiparous subjects. No other differences were evident between primiparous and multiparous women apart from high-density lipoprotein cholesterol levels, which were slightly decreased in the latter subjects. Conclusions: Our results show that during normal pregnancy, the increase in plasma triglycerides may lead to the appearance of the atherogenic dense low-density lipoproteins in a subgroup of women. We suggest that the observed changes in low-density lipoprotein patterns during pregnancy might be used to identify those women who later in life will have these atherogenic small and dense low-density lipoproteins. (Am J Obstet Gynecol 1999;181:430-4.)