Previous research has not adequately addressed how gay and lesbian couples emotionally negotiate unequal biological ties to their children. Because each co-parent has the potential to be their child's biological parent and because same-sex couples highly value relationship equality, unequal biological ties to children may cause feelings of jealousy between co-parents. To counter this, increasing numbers of lesbian couples have been using in-vitro fertilization (IVF) to biologically co-mother, using the eggs of one partner and the womb of the other. While hardly common, this strategy can affect the emotional dynamics between the co-mothers and their children. This article explores how variables common to many lesbian-led families (including method of conception) may contribute to or protect against jealousy. Presented data comes from an 18-month ethnographic study of 30 lesbian-led families with young children living in a major northeastern city. Ten couples adopted infants, 10 couples used assisted insemination (AI), and 10 couples used IVF to biologically co-mother. Lesbians' use of IVF to co-mother has not been previously studied. Methods included in-depth interviews, participant observation, and self-administered questionnaires. Couples who adopted or used IVF reported less jealousy than couples who conceived using AI. Factors that correlate with the likelihood of experiencing maternal jealousy include both partners wanting to be a birth mother, perceptions of unequal biological ties to children, and infertility. Professionals serving lesbian co-mothers should be sensitive to the presence and absence of the above factors.