Objectives: Most research evaluating relationships between social network attributes and loneliness have focused on older adult and adolescent networks. The present study examines the relationships between social network size (number of relationships), social network density (whether named relationships are connected to one another) and maternal loneliness during pregnancy. Methods: Eligible women were enrolled at the time of their dating ultrasound (between 8 and 12 weeks of gestation). Interested women provided written consent and completed demographic, social network and loneliness measures. Participants completed the same surveys in their third trimester. Mixed-regression models, adjusted for age, race, ethnicity, and insurance type, were used to assess the relationship between social network size, network density, and loneliness. Results: A total of 94 pregnant women (mean age = 23.77, 70.2% Black, 87.2% public insurance) completed baseline study measures, and 60 participants completed both assessment time points. Completers and non-completers did not differ on key characteristics. Social network density, but not social network size, predicted maternal loneliness (β= − 1.27, 95% CI − 2.53, − 0.01, p = 0.0489) in the first and third trimester. Conclusions: These findings indicate that pregnant women’s social network density may be more intimately related to feelings of loneliness than the objective number of relationships. This knowledge can begin to inform the design of supportive approaches to improve women’s health.