Condition category
Urological and Genital Diseases
Date applied
Date assigned
Last edited
Prospectively registered
Overall trial status
Recruitment status
No longer recruiting

Plain English Summary

Background and study aims
Literature confirms that fast developing blastocysts [blastocyst is a highly differentiated, highly developed embryo that has grown to the point where it is ready to attach to the uterine wall (implantation)] transferred on day 5 are associated with good pregnancy rates. The dilemma arises if there are no fast developing expanded blastocysts for transfer seen on day 5. What is the optimal time for transfer of these embryos? Would it be correct to transfer the best available less expanded embryos on day 5 or replace delayed blastocysts on day 6? There have been no studies to compare the implantation potential of slow developing day 5 blastocysts transferred on day 5 with those transferred on day 6. The aim of this study is to ascertain if differences exist in pregnancy outcomes in the two groups both with slow developing embryos on day 5: transfer of fresh day 5 slow developing embryos compared to transfer of day 6 fully developed blastocysts transferred on day 6.

Who can participate?
Women aged 21-45 undergoing in vitro fertilisation (IVF)/intra-cytoplasmic sperm injection (ICSI) treatment and reaching a day 5 embryo transfer but with no fast developing blastocysts on day 5 will be eligible to participate in the study.

What does the study involve?
Participants are randomly allocated into two groups. They either have an embryo transfer on day 5 or extended embryo culture and embryo transfer on day 6.

What are the possible benefits and risks of participating?
The participant may benefit from an improved pregnancy rate if allocated to a group which is later found to be superior to the other group. Embryo transfer is a part of routine treatment. The research protocol will only change the time of the embryo transfer. Hence there will be no additional risks or burdens of the research for the participant.

Where is the study run from?
The study will be carried out in a tertiary referral teaching university fertility unit

When is the study starting and how long is it expected to run for?
We aim to start the study by February 2013 and it is expected to last between 12-18 months

Who is funding the study?
Homerton University Hospital NHS Foundation Trust (UK)

Who is the main contact?
Dr Priya Bhide, Associate Specialist, Homerton University Hospital

Trial website

Contact information



Primary contact

Prof Roy Homburg


Contact details

Homerton Fertility Centre
Homerton Row
E9 6SR
United Kingdom

Additional identifiers

EudraCT number number

Protocol/serial number


Study information

Scientific title

When is the best time to replace slow developing embryos? A comparison between day 5 and day 6 transfers: a randomised controlled trial


Study hypothesis

Embryo implantation involves the complex interplay between the receptivity of the womb lining and embryo quality. The developmental potential of slower developing embryos is similar to faster developing ones as shown by similar outcomes for frozen embryos replaced in frozen embryo replacement cycles (Shapiro et al). However embryos with a faster developmental pace transferred on day 5 in a fresh cycle give an advantage in terms of clinical pregnancy rate over slower developing embryos transferred on day 6 (Shapiro et al). This suggests that delayed fresh transfers may have a suboptimal outcome due to embryo-endometrial asynchrony. The dilemma arises if there are no fast developing embryos for transfer seen on day 5. There have been no randomised control trials which would point to the best timing for replacement of slow embryos in these women. Would it be correct to transfer the best available embryos on day 5, or replace embryos on day 6 after delayed culture?

Ethics approval

Not provided at time of registration

Study design

Pilot randomised controlled trial

Primary study design


Secondary study design

Randomised controlled trial

Trial setting


Trial type


Patient information sheet

Not available in web format, please contact Dr Priya Bhide ( to request a patient information sheet


Subfertility patients undergoing IVF / ICSI treatment


All participants will follow the routine IVF/ICSI protocol till the day of embryo transfer. Following this they will be allocated to either of the two study arms.

Study arm 1: patient to have embryo transfer on day 5
Study arm 2: patient to have extended embryo culture and transfer of embryos on day 6

Following embryo transfer all participants will again follow routine clinical care protocols standard to IVF.

Intervention type



Not Applicable

Drug names

Primary outcome measure

Clinical pregnancy rate

Secondary outcome measures

Delayed blastocyst conversion rate

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

Women age 21-45 undergoing a single IVF / Intra-cytoplasmic sperm injection (ICSI) treatment with their own oocytes during the specified study duration who:
1. Proceed to have a day 5 transfer
2. Have no fast developing embryos for transfer on day 5

Participant type


Age group




Target number of participants


Participant exclusion criteria

Women who have already participated in the study for a previous cycle

Recruitment start date


Recruitment end date



Countries of recruitment

United Kingdom

Trial participating centre

Homerton Fertility Centre
E9 6SR
United Kingdom

Sponsor information


Homerton University Hospital NHS Foundation Trust (UK)

Sponsor details

Homerton Hospital
Homerton Row
E9 6SR
United Kingdom

Sponsor type

Hospital/treatment centre



Funder type

Hospital/treatment centre

Funder name

Homerton University Hospital NHS Foundation Trust (UK)

Alternative name(s)

Funding Body Type

Funding Body Subtype


Results and Publications

Publication and dissemination plan

Not provided at time of registration

Intention to publish date

Participant level data

Not provided at time of registration

Basic results (scientific)

Publication list

Publication citations

Additional files

Editorial Notes

06/07/2018: No publications found, verifying study status with principal investigator 10/05/2016: No publications found, verifying study status with principal investigator.