Trial Search Results

Natural Versus Programmed Frozen Embryo Transfer (NatPro)

NatPro is a two-arm, parallel-group, multi-center, randomized trial in which women undergoing FET will be randomized to receive either a modified natural cycle (corpus luteum present) or a programmed cycle (corpus luteum absent).

Stanford is currently accepting patients for this trial.

Lead Sponsor:

JHSPH Center for Clinical Trials

Stanford Investigator(s):


  • Procedure: Modified natural cycle
  • Procedure: Programmed cycle


Phase 3


Inclusion criteria

To be eligible, subjects must meet all these criteria:

   - Age 18-39 years at the time that embryos were created if no pre-implantation genetic
   testing (PGT) testing was performed. If PGT testing was performed and indicates that
   an embryo is euploid, the patient can be included if she was age 18-41 years at the
   time that the embryo was created.

   - Age 18-41 years at the time of the frozen embryo transfer (FET) as advancing age
   itself becomes a significant risk for preeclampsia

   - Normal uterine cavity as assessed by saline infusion sonohysterogram,
   hysterosalpingogram, or hysteroscopy within one year of the enrollment visit, and
   repeated at the discretion of the investigator

   - Regular menstrual cycle length (approximately 24-35 days) indicative of ovulatory

   - Willing to undergo elective single embryo transfer

   - Body Mass Index<=40

   - If Body Mass Index is over 30 or individual has other risk factors for diabetes,
   normal hemoglobin A1c

   - Prior to enrollment, participant will have at least one vitrified blastocyst with
   euploid result by pre-implantation genetic testing (PGT-A) or at least one vitrified
   blastocyst of fair or better morphologic quality if no PGT-A results are available.

   - Willingness to be randomized to either a modified natural or programmed cycle, with a
   willingness to administer daily intramuscular progesterone in oil if assigned to the
   programmed cycle.

   - Normal thyroid stimulating hormone (TSH) , according to local laboratory standards,
   within one year of study enrollment and repeated at the discretion of the
   investigator. Use of thyroid medication is permitted.

Exclusion criteria

To be eligible, subjects must not meet any one of these criteria:

   - Medical contraindication to pregnancy

   - Embryos created using donor oocytes

   - Embryo donation

   - Gestational carrier

   - Reciprocal In vitro fertilization (IVF) (one female partner carrying pregnancy, other
   female partner as source of eggs)

   - Embryos created from frozen oocytes

   - Recurrent implantation failure defined as no clinical pregnancy with ≥2 prior
   consecutive embryo transfers unless patient also had successful live birth with IVF

   - Anti-phospholipid antibody syndrome or rheumatologic disease requiring chronic
   systemic medications

   - Uncontrolled diabetes mellitus

   - History of >1 pregnancy loss in the second or third trimester

   - Uncontrolled hypertension

   - Untreated hydrosalpinx (i.e., hydrosalpinx in situ which has not been ligated or

   - Physician recommendation to perform the embryo transfer outside of the timing
   specified by the protocol

   - Contraindication to any medication which must be used in preparation for the frozen
   embryo transfer (i.e., estradiol, progesterone, Human chorionic gonadotropin (hCG)).

Ages Eligible for Study

18 Years - 41 Years

Genders Eligible for Study


Now accepting new patients

Contact Information

Stanford University
School of Medicine
300 Pasteur Drive
Stanford, CA 94305
Alma Gonzalez