lactation pregnancy breastfeeding test positive current year women standards time breastfeeding pregnancy current active women reported self planning possibility intention breastfeeding pregnancy test negative pregnant entry days study childbearing women pregnancy pregnant test women positive breastfeeding serum lactating study urine pregnant planning feeding breast breastfeeding study months pregnancy female lactating feeding pregnancy breast test positive unwillingness women known urine effective breastfeeding women lactating study participants eligible registration time zydelig fancd pregnancy test positive women serum administration enrollment product wocbp urine