The U.S. Open will not penalize players whose rankings have tumbled because of pregnancy-related breaks from the game in awarding seeds for its women’s field, starting with this year’s tournament. But it’s unclear how the U.S. Tennis Association will strike a fair balance between the interests of returning mothers whose rankings have slid and active players who have surged ahead of them in the interim. The decision in principle, first reported by The New York Times, follows criticism leveled at French Open officials in May for not seeding its three-time champion Serena Williams in her return to competition after giving birth to a daughter in September.