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Micronised progesterone luteal-phase support improves live birth rates in women with unexplained infertility

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What is this trial about?

A plain-language summary of the goals, design and what participants do

The study focuses on couples where the woman has unexplained infertility, meaning they have been trying to become pregnant for a year or more without a clear medical reason. The medication being tested is a soft vaginal capsule that contains micronised progesterone, given during the luteal phase (the part of the menstrual cycle after ovulation) to see if it helps achieve a live birth. A matching placebo capsule that looks the same but does not contain the hormone is also used.

The purpose is to find out whether adding this hormone support increases the chance of a baby being born alive compared with taking no active medication. Participants are randomly assigned to receive either the hormone capsule or the placebo for up to six months while trying to become pregnant naturally. Pregnancy outcomes, any side effects, and quality of life are recorded, and participants are followed for up to 18 months after the start of the study.

The research process

The trial runs in 8 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Randomisation and receipt of study medication

    After joining the study you are randomly assigned to receive either the active product utrogestan 300 mg soft vaginal capsules or a matching placebo.

    The study medication is provided in identical looking soft capsules so that you cannot know which one you have received.

  2. Step 2

    Start of medication

    You insert the vaginal capsules each day, usually in the evening, to deliver a total dose of 600 mg of progesterone (two 300 mg capsules) per day.

    The capsules are placed inside the vagina according to the written instructions that accompany the medication.

    The treatment continues for up to six months or until a pregnancy is confirmed, whichever occurs first.

  3. Step 3

    Daily medication diary

    You keep a daily record, called a medication diary, noting each time the capsule is taken and any side effects you experience.

    The diary helps the study team assess how well the medication is tolerated.

  4. Step 4

    Six‑month questionnaire on side effects and compliance

    At six months after randomisation you receive a questionnaire that asks about any side effects, how consistently the medication was used, and overall satisfaction with the treatment.

  5. Step 5

    Quality‑of‑life assessments

    You complete the same quality‑of‑life questionnaire (the fertiqol) at three time points: when you are randomised, at six months, and again at eighteen months after randomisation.

    These questionnaires measure how the study and any pregnancy affect your well‑being.

  6. Step 6

    Pregnancy monitoring

    If a pregnancy occurs within the six‑month treatment period, you are followed to record the type of pregnancy (clinical, ongoing, biochemical), any loss, and details of the birth.

    Information such as multiple pregnancy, time to pregnancy, pregnancy complications, delivery method, and newborn outcomes is collected.

  7. Step 7

    Follow‑up for assisted reproductive techniques

    Twelve months after randomisation you are asked whether any assisted reproductive techniques (such as iui, ivf, or icsi) were used and whether they resulted in a pregnancy.

    This information is used to compare the need for further treatment between the two groups.

  8. Step 8

    Study closeout

    After the final data collection at eighteen months, the study is closed and the overall results are analysed.

    No further actions are required from you after the last questionnaire.

Who can join the trial?

8 criteria

  • Be a woman with a BMI (body weight compared to height) less than 45 kilograms per square meter.
  • Be at least 18 years old.
  • Have been following expectant management (watchful waiting without active treatment) for at least six months according to Dutch guidelines.
  • Have a Hunault prognostic score (a calculation that predicts the chance of getting pregnant naturally) of 30% or higher.
  • Have experienced infertility (trying to become pregnant for at least one year without success), whether it is the first time or after a previous pregnancy.
  • Have a regular menstrual cycle that lasts between 21 and 35 days.
  • Have a total motile sperm count (the number of moving sperm) of at least 10 million per milliliter in the partner’s semen analysis.
  • Have no known risk of tubal pathology (problems with the fallopian tubes), or if there is a risk, it must be ruled out by a tubal patency test (a test that checks if the tubes are open).

Who cannot join the trial?

5 criteria

  • If you have untreated problems in the uterus, such as growths called endometrial polyps (small tissue growths inside the lining of the uterus) or submucosal fibroids (benign muscle tumors that grow just under the lining of the uterus), you cannot join the study.
  • If you do not understand Dutch or English well enough, and cannot receive study information through a certified translator, you cannot join the study.
  • If you are unable or unwilling to sign a written agreement that you understand the study (called informed consent), you cannot join the study.
  • If you have a medical reason that makes using vaginal progesterone unsafe (called a contraindication), such as an allergy to peanuts or soy, you cannot join the study.
  • If you have been officially diagnosed with endometriosis (a condition where tissue similar to the lining of the uterus grows outside the uterus), you cannot join the study.
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Investigated drugs

Progesterone is a hormone given in soft vaginal capsules during the luteal phase of the menstrual cycle. In this study it is used to support the lining of the uterus in women with unexplained infertility, with the goal of improving the chances of a live birth. The medication is placed inside the vagina, where it is absorbed locally and helps create a more favorable environment for a fertilized egg to implant and grow.

What is already known about the treatment

Utrogestan 300 mg soft vaginal capsules - These soft capsules are inserted into the vagina, where they dissolve and release micronised progesterone that is absorbed locally. Progesterone in this form is an approved and widely used medication for supporting the luteal phase of the menstrual cycle and for helping maintain early pregnancy. It works by supplying the same hormone the body makes after ovulation, which thickens the uterine lining and makes it ready for an embryo to implant. The drug belongs to the class of progestogens, a type of hormone therapy.

Investigated diseases

Unexplained infertility - A condition where a woman and her partner have been trying to conceive for a defined period (typically 12 months or 6 months if the woman is over 35) without success, and standard medical tests do not reveal a clear cause. The diagnosis is made after evaluating both partners and ruling out common factors such as hormonal imbalance, structural problems, or sperm abnormalities. The condition may remain unchanged, with continued difficulty achieving pregnancy, or it may resolve spontaneously in some couples over time. Ongoing attempts to conceive can lead to repeated cycles of trying and not becoming pregnant. The situation often prompts couples to consider further observation or additional reproductive options.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2026-525747-33-00Protocol codeV0003925Estimated enrolment640 patientsSponsorUniversitair Medisch Centrum Utrecht

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