In Johnson v. Calvert (1993) 5 Cal. 4th 84, a married couple, Mark and Crispina Calvert, executed an agreement with Anna Johnson to have an embryo created by the sperm of Mark and the egg of Crispina implanted in Anna. The child born was by the terms of the contract to be the Calverts' child, and Anna relinquished all parental rights to the child. Relations deteriorated between the parties during the pregnancy and both the Calverts and Anna Johnson filed actions seeking declarations they were the parents of the unborn child. In considering the competing claims of Crispina and Anna to be the natural mother pursuant to Civil Code former section 7003, subdivision (1) (now Fam. Code 7610, subd. (a)), the court found that California law recognizes only one natural mother. (Johnson v. Calvert, supra, 5 Cal. 4th at p. 92, fn. 9.) Because both women presented acceptable proof of maternity, neither more compelling than the other, the court looked to the writings of several legal commentators and agreed that " 'within the context of artificial reproductive techniques,' . . . 'intentions that are voluntarily chosen, deliberate, express and bargained-for ought presumptively to determine legal parenthood.' " (Id., at p. 94, quoting Schultz, Reproductive Technology and Intent-Based Parenthood: An Opportunity for Gender Neutrality (1990) Wis. L.Rev. 297, 323.) The court concluded that in deciding the issue of maternity, it would look to the intentions of the parties as expressed in the surrogacy contract. (Johnson v. Calvert, supra, at p. 95.)