Our helpline: 01924 200799 Mon, Tue, Thu 9am-4pm | Wed, Fri 9am-8pm

The PRISM trial

The results of the PRISM trial (progestersone in early pregnancy bleeding) were published in the New England Journal of Medicine on 9 May 2019.

The results showed that overall, among women with bleeding in early pregnancy, treatment with progesterone during the first trimester did not result in a significantly higher incidence of live births than amongst those who had a placebo (a pessary with no active ingredients).

Further analysis, however, showed that a sub-group of women with a history of recurrent miscarriage (three or more miscarriages before this pregnancy), did show a significant improvement in outcome for those who had the progesterone treatment. There was also a small improved outcome for those who had previously had one or two miscarriages.

November 2021: a new recommendation

On 24 November 2021, NICE, the National Institute of Health and Care Excellence, published new guidance [1] recommending treatment with progesterone for women with early pregnancy bleeding and at least one previous miscarriage.

Based on a systematic review of research studies[2], including the PRISM trial, the guidance includes new recommendations on the use of progesterone for women who have vaginal bleeding in early pregnancy and have had one or more previous miscarriages.

The recommendations are very specific:


A bit more information

The NICE guidance does not recommend progesterone treatment for

It does, however, recommend further research into

If you have any questions or concerns about the research or about possible treatment with progesterone, please do consult your GP or Early Pregnancy Unit.

If it might help just to talk, please do get in touch. You’ll find information about how we can help here.


Notes and references:

[1] www.nice.org.uk/guidance/ng126

[2] A Cochrane’s network meta-analysis – a review that combines data from several different studies

[3] Micronised progesterone is identical in structure to naturally produced progesterone


We provide information about the trial background below, and further down the page you can read comments from two women who took part in the trial.

About the PRISM trial

PRISM was a randomised, double-blind, placebo-controlled trial:

Randomised: The women who take part were given either the treatment drug (progesterone) or a placebo – a dummy drug that has no active ingredients. A computer made the selection so it was completely random.

Double-blind: The women in the study weren’t told whether they are taking the active medicine or the placebo – and neither were their doctors. So both were blinded to this information.

Placebo-controlled: Half the women in the study had the active medicine and half (the controls) had the placebo. The medicine that they received looked exactly the same to them and their doctors, but a completely separate group kept a record of which women had progesterone and which had the placebo.

Other information

Who could take part?

The researchers recruited women who:

What did participants need to do?

Women who agreed to take part were given a pack of capsules and asked to insert two capsules twice a day (morning and evening) into their vagina until 16 weeks of pregnancy.

The trial team collected most of their study information from hospital notes but may have made individual contact to check some details.

You can read Amanda and Faye’s accounts of taking part in the trial, at the bottom of this page.

Where did it take place?

The trial recruited women from 48 centres across England and Scotland:

Some personal views

Amanda took part in the PRISM trial. She writes:

At 6 weeks pregnant I was bleeding and went to the Early Pregnancy Unit at University College Hospital, London. Here I was offered the chance to take part in the PRISM trial.

With the potential outcome of not miscarrying I was very keen to learn more. I was told about the possible side effects, and also that I might only be taking a placebo. I read up on how successful taking progesterone only has been in other countries. I felt that it was a great opportunity to not only support the trial for women in this country but also giving my fetus an extra chance of not miscarrying. So I agreed to take part.

During the trial I was given fantastic one to one advice from the PRISM research team. It was extremely reassuring knowing that I had a point of contact thought my pregnancy, someone who I could contact any time. She was easy to talk to and answered any of my questions, putting my mind at rest. I also had additional scans, to see the progress of my fetus, which was fantastic.

I was a little uncomfortable about using the (vaginal) pessaries to start with and worried – would I use them properly, would they have side effects. After literally 24 hours I was inserting the pessaries with ease and with no discomfort. I found wearing a pantie liner useful for any discharge that I had.

I travel a lot for work which was another worry but taking the pills didn’t affect my day to day life at all.

I don’t know if I took the progesterone or a placebo, but I am so pleased that I was lucky enough to take part in the trial. I am now 38 weeks pregnant, with a healthy baby girl on her way.

Faye also took part in the PRISM trial, and writes:

I was signed up to the PRISM trial after having bleeding in early pregnancy. After experiencing three miscarriages since the birth of my son it was a relief to feel like we were doing something proactive in this pregnancy.

I obviously don’t know whether the trial made a difference to this pregnancy’s outcome, but I was absolutely delighted when our baby daughter was born. We’ve waited two years for her arrival and experienced a lot of heartache along the way so I just wanted to say thank you for offering hope to more parents through these trials.