Higher cumulative exposure to clomiphene citrate was linked to miscarriage and multiple births, without improving live birth rates in a large US study.
A fertility drug used for nearly six decades may reach a point where more treatment brings greater risk, but no better chance of taking home a baby.
Researchers who examined more than 21,000 in vitro fertilisation (IVF) embryo transfer cycles found that higher cumulative exposure to clomiphene citrate was associated with an increased risk of miscarriage and multiple births. Yet the likelihood of a live birth did not significantly improve.
It is not conclusive that clomiphene directly caused these negative outcomes, but they raise questions about repeated or escalating treatment, particularly when a patient has already received several courses of the drug.
What Is Clomiphene Citrate, and Why Is It Prescribed?
Clomiphene citrate, sometimes sold under the brand name Clomid, is an oral medicine used to stimulate ovulation. It is generally prescribed to women who do not ovulate regularly, including some people with polycystic ovary syndrome.
The medicine alters the way the body responds to oestrogen. This prompts the release of hormones that encourage ovarian follicles to grow and release an egg.
For some patients, a relatively low dose is enough to trigger ovulation. Those who do not respond may receive a higher dose or further treatment cycles, increasing their total exposure over time.
Clomiphene remains an important fertility medicine. Infertility affects around one in six adults worldwide, and clomiphene plays a substantial role in fertility care across Asian region.
However, the latest findings suggest that the drug’s benefits and risks may shift as cumulative exposure rises.
How Did Higher Doses Affect Miscarriage Risk?
The US national cohort study, published in BMJ Open, analysed 21,004 IVF embryo transfer cycles recorded between 2004 and 2021.
The researchers grouped the cycles according to how much clomiphene the women had previously received.
Compared with women in the lowest exposure group, those who had received a cumulative dose of 500 to 749 milligrams (mg) had a 12% higher risk of miscarriage. At cumulative doses of 750 to 999 mg, the risk was 38% higher.
Women exposed to at least 750mg were also more than twice as likely to have twins or another multiple birth.
This matters because twins and higher-order multiple pregnancies carry greater risks than singleton pregnancies. Possible complications include premature birth, low birth weight and pregnancy-related high blood pressure. The goal of fertility care is not pregnancy at any cost – it is one healthy birth, achieved as safely as possible.
Did More Clomiphene Improve Live Birth Rates?
As cumulative exposure increases, there was no significant improvement in live birth rates. This creates a difficult trade-off. A patient may undergo more treatment in the hope of improving her chances, while the additional exposure may offer little benefit and could even be linked to poorer pregnancy outcomes.
The study also found that spontaneous abortion became more common with greater exposure. Stillbirth appeared to be more than three times as common in the highest-dose group, although this result was not statistically significant.
Only a small number of women fell into that exposure category. The researchers therefore could not rule out chance, and larger studies will be needed before firm conclusions can be drawn.
Does Clomiphene Cause Miscarriage?
The study was an observational analysis and thus not able to establish cause and effect. There are many factors that can affect one’s risk of miscarrigae – for example, women who receive more clomiphene may differ biologically from those who require less treatment. They may have more difficult-to-treat infertility or other characteristics that also influence pregnancy outcomes.
The analysis involved IVF cycles in the United States. Its findings may not translate directly to every fertility patient or treatment setting, including clinics in Asia.
It also does not mean that patients should stop prescribed medicine on their own. Clomiphene has helped many people ovulate and become pregnant when used for an appropriate reason under medical supervision.
Instead, the findings support closer attention to cumulative exposure, treatment response and whether continuing the same approach remains worthwhile.
How Long Should Clomiphene Treatment Continue?
US prescribing information recommends starting with 50mg daily for five days. The dose may be increased to 100mg daily for five days if ovulation does not occur. Increasing the dosage or duration beyond that level is not recommended. Long-term cyclic treatment should generally not continue beyond about six cycles.
The label also states that once ovulation occurs at a particular dose, raising the dose during later cycles offers no advantage.
Individual treatment plans can differ, and patients should follow guidance from their fertility specialist. Appropriate monitoring may include checking whether ovulation occurred and assessing the ovaries between cycles.
What Should You Ask Your Fertility Doctor?
Fertility treatment can be emotionally and physically demanding, especially when one cycle leads to another. If you have taken clomiphene more than once, ask your doctor how much you have received in total and whether it is working as expected.
It may also help to ask:
- What are my chances of success if I continue?
- Has my risk of miscarriage or a multiple pregnancy changed?
- At what point should we consider a different approach?
Every fertility treatment comes with its own benefits, risks and unanswered questions, so a newer medicine is not automatically safer or more effective. Furthermore, more treatment does not always mean a better outcome. Each new cycle should have a clear purpose, with the decision made together by you and your fertility doctor.
