Inclusion Criteria:  Age > 18 years < 40 years BMI < 35 kg/m2 Normal wet smear within the past three years Thawed blastocysts (day 5) after either IVF or ICSI treatment  Exclusion Criteria:  Age < 18 years BMI > 35 kg/m2 Day 6 blastocysts Oocyte donation HIV/ hepatitis Undiagnosed vaginal bleeding Uterine malformations Persisting ovarian cysts Tumors in Hypothalamus, pituitary, thyroid or adrenal Previous breast cancer BRCA1/2 Unregulated thyroid disease Cardiovascular disease Breast feeding Present or previous chemotherapy/radiation therapy Present or previous malignant disease Smoking Alcohol/drug abuse