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Cryo-thawed embryo transfer: natural versus artificial cycle. A non inferiority trial.

Go to the ANTARCTICA website

Endometrium preparation in patients undergoing frozen thawed embryo transfer can be achieved in several ways. The two most common used methods in the Netherlands are the artificial cycle using hormonal substitution versus the natural cycle using ultrasound based ovulation induction. Pregnancy rates in both methods are supposed to be equal.


Regretfully there are no randomized controlled trials supporting this believe. Aim of this trial is therefore to compare live birth rates between patients undergoing artificial cycle frozen-thawed embryo transfer (FET) versus patients undergoing natural cycle FET.

Study design
non-inferiority, randomized controlled trial.

Study population
Patients between 18 and 40 receiving FET after regular IVF or IVF-ICSI treatment.


intervention 1: ultrasound monitored natural cycle FET.

Intervention 2: artificial cycle FET using estrogen/progesterone substitution without downregulation.


Outcome measures
primairy outcome: live birth rate

Secundairy outcome: clinical and ongoing pregnancy rate, cancellation rate, cost-efficiency, perceived burden.

Power/data analysis

1150 patients need to be included in order to meet statistical power. Calculations are based on a pregnancy rate of 20 %, a clinical important difference of 7 %, type I error of 5 % and a type II error of 80%. Data analysis will be performed using both a per protocol analyses as well as a intention to treat analyses.

Economic evaluation
Cost-efficiency will be calculated.

Time schedule
March of 2009 inclusion is started, aim is to meet the necessary inclusion in march 2012.

dr. B.J. Cohlen, gynaecologist at Fertility centre Isala klinieken

drs. E.R. Groenewoud, researcher at Fertility centre Isala klinieken

educational grand Organon BV, Oss, the Netherlands.



For questions please contact drs. E.R. Groenewoud, researcher.

Email: e.r.groenewoud@umcg.nl  

Phonenumber: 06-50252309