Fertility Medications and Twin Risk: Why Letrozole, Clomiphene and Gonadotropins Are Not the Same

Quick answer: Fertility medications can increase the likelihood of twins or a higher-order multiple pregnancy, but letrozole, clomiphene citrate (Clomid), and gonadotropins do not have one fixed or interchangeable twin-risk percentage. The risk seen in studies depends not only on the medication, but also on how the ovaries respond, how many follicles develop, the treatment protocol, the population being treated, and how the study calculates its outcome.

In general, gonadotropin ovarian stimulation has raised greater concern about multiple gestation than oral medications such as letrozole or clomiphene, particularly when treatment produces a multifollicular response. The comparison between letrozole and clomiphene is more nuanced: different studies have produced different numerical results, and some major comparisons have not shown a statistically significant difference in twin pregnancy.

For the broader role of fertility treatment in twin probability, see our guide to fertility medications and twin probability.

Important context: A percentage reported in a fertility study is a population-level research result, not a personalized prediction of an individual’s chance of having twins.

Quick comparison

Feature	Letrozole	Clomiphene / Clomid	Gonadotropins
Medication class	Aromatase inhibitor	Ovulation-inducing medication that affects estrogen signaling	Injectable hormones used to stimulate follicular development
Common fertility context	Ovulation induction and some ovarian-stimulation protocols	Ovulation induction and ovarian-stimulation protocols	Ovarian stimulation
Typical concern for multiples	Multiple pregnancy is possible, but estimates vary by population and study	Multiple pregnancy is possible; older and newer estimates do not all agree	Greater concern for multifollicular development and multiple gestation in many treatment settings
Key variable beyond the drug	Ovarian response and follicle number	Ovarian response and follicle number	Ovarian response, follicle number, dose strategy, monitoring, and protocol
Main interpretation caution	Do not turn one PMOS/PCOS study result into a universal letrozole twin rate	Do not treat the traditional 8% to 10% figure as the only valid modern estimate	Do not turn a broad multiple-pregnancy figure into a universal twin percentage

How Fertility Medications Can Affect Twin Risk

The connection between fertility medication and twins is easier to understand when the focus shifts from the name of the drug to the ovaries’ response to treatment.

Each ovarian follicle contains a developing egg. In an unassisted menstrual cycle, one follicle commonly becomes dominant and releases an egg. Fertility medications can alter that process. Depending on the medication, treatment goal, individual response, and protocol, more than one follicle may develop sufficiently to have the potential to ovulate.

If more than one egg is released and more than one is fertilized, a dizygotic, or fraternal, twin pregnancy can result. This is why multiple-follicle development is central to understanding treatment-related twin risk.

The pathway can be summarized as:

Fertility medication → ovarian response → follicular development → potential multiple ovulation → possibility of twin or higher-order multiple pregnancy.

None of those steps guarantees the next. Developing more than one follicle does not mean that multiple eggs will necessarily be released, fertilized, implant successfully, or produce an ongoing multiple pregnancy.

Ovulation Induction vs Ovarian Stimulation

Ovulation induction and ovarian stimulation are related terms, but they should not automatically be treated as synonyms.

Ovulation induction is commonly used when treatment is intended to induce or restore ovulation in someone who is not ovulating regularly. Ovarian stimulation can also be used in people who already ovulate, with the aim of encouraging follicular development during a treatment cycle.

Letrozole and clomiphene are oral medications used in these treatment contexts. Gonadotropins provide more direct hormonal stimulation and may produce a stronger or more multifollicular ovarian response depending on the protocol.

This distinction matters because a twin-risk statistic from one type of treatment cannot automatically be transferred to a different treatment setting.

From Ovarian Response to Multiple Follicles

The medication itself is only one variable. What happens after the medication is given is crucial.

A person may have a relatively limited, monofollicular response, meaning one main follicle develops, or a multifollicular response, in which several follicles develop. Research on ovarian stimulation consistently shows that the number of mature follicles is strongly related to the likelihood of multiple gestation.

This helps explain why two people receiving the same medication, or two clinical trials studying the same medication, may not have identical multiple-pregnancy outcomes.

Letrozole and Twin Risk

Letrozole is an aromatase inhibitor. By reducing estrogen production, it can alter hormonal feedback involved in ovarian activity and is used in fertility care to support ovulation or follicular development in appropriate treatment settings.

Searches for a single “letrozole twin percentage” often lead to one number quoted from one study. That can be misleading because major letrozole studies have involved different populations and treatment designs.

What Studies in PMOS, Formerly PCOS, Have Found

Polyendocrine Metabolic Ovarian Syndrome, or PMOS, is the current name for the condition previously known as Polycystic Ovary Syndrome, or PCOS. The international terminology changed in May 2026. Historical research naturally uses the older PCOS name, so both terms are relevant when discussing the evidence.

A major randomized trial published in 2014 compared letrozole with clomiphene in 750 women with infertility associated with what was then called PCOS. Among resulting pregnancies, twin pregnancy occurred in 4 of 117 pregnancies with letrozole, or 3.4%, compared with 6 of 81 pregnancies with clomiphene, or 7.4%.

The numerical result was lower with letrozole, but the difference in twin pregnancy was not statistically significant. That is an important qualification. The trial supports saying that fewer twin pregnancies were observed in the letrozole group, but it does not justify presenting 3.4% and 7.4% as universal drug-specific twin probabilities or claiming that the trial conclusively established a lower twin rate with letrozole.

What Studies in Unexplained Infertility Have Found

A different picture emerged in the large AMIGOS trial involving women with unexplained infertility undergoing ovarian stimulation.

Among ongoing pregnancies with fetal heart activity, multiple gestation occurred in:

• 9 of 67 letrozole pregnancies, or 13%
• 8 of 85 clomiphene pregnancies, or 9%
• 34 of 107 gonadotropin pregnancies, or 32%

All multiple gestations in the letrozole and clomiphene groups were twins. The gonadotropin group included both twins and triplets.

Letrozole’s multiple-gestation rate was significantly lower than the gonadotropin rate, but it did not differ significantly from clomiphene in that trial.

These numbers should not be placed beside the PMOS/PCOS figures without explanation. The populations, treatment settings, and outcome denominators are different.

Why Letrozole Does Not Have One Universal Twin Rate

The often-quoted 3.4% figure answers a specific question about pregnancies in a particular PMOS/PCOS trial. The 13% figure from the unexplained-infertility study answers a different question in a different population and among a different outcome group.

They are not competing estimates of one universal biological constant.

A more accurate conclusion is that letrozole can be associated with twin pregnancy, but the observed rate varies with the patient population, ovarian response, treatment context, study design, and denominator.

Clomiphene / Clomid and Twin Risk

Clomiphene citrate, commonly known by the brand name Clomid, has long been associated with an increased chance of multiple pregnancy compared with conception without fertility treatment.

Clomiphene influences estrogen signaling and the hormonal pathways involved in ovulation and follicular development. As with letrozole, the clinically important question is not simply whether the medication was used, but how the ovaries responded.

Why the Familiar Clomid Twin Percentage Varies

Many fertility resources have historically quoted a multiple-pregnancy rate in the range of roughly 8% to 10% with clomiphene. That figure is useful as historical context, but newer research shows why it should not be treated as one fixed modern rate.

An official clomiphene drug label reports older clinical-study data in which multiple pregnancies included twins as well as a small number of triplet and higher-order pregnancies. These data helped establish the long-standing association between clomiphene and multiples.

However, a systematic review of contemporary single-agent clomiphene treatment for WHO group II ovulatory disorders found an overall multiple-pregnancy rate of 3.8%, consisting of 3.6% twins and 0.2% triplets. The authors specifically noted that many older estimates came from treatment practices that did not reflect more recent guidelines.

A much larger nationwide cohort published in 2025 found multiple pregnancy in 5.2% of clomiphene-exposed pregnancies, compared with 1.4% in matched unexposed pregnancies. Twin pregnancies accounted for 5.1% of exposed pregnancies, while triplet-or-higher pregnancies were much less common.

These estimates differ, but that does not necessarily mean one source is correct and the others are wrong.

Older Estimates vs Contemporary Evidence

Evidence	Population / Context	Reported Outcome	What It Tells Us
Older clomiphene clinical-label data	Historical clinical experience	Multiple pregnancies including twins and higher-order multiples	Established the long-standing association between clomiphene and multiple gestation
2022 systematic review	Single-agent clomiphene for WHO group II ovulatory disorders	3.8% multiple pregnancy, mostly twins	Suggests contemporary use may produce a lower rate than frequently quoted older figures
2025 nationwide cohort	Clomiphene-exposed pregnancies compared with matched unexposed pregnancies	5.2% multiple pregnancy; 5.1% twins	Provides large contemporary real-world evidence that the risk remains elevated but is not captured by one historical number

The difference can reflect study era, treatment practices, monitoring, patient selection, outcome definitions, and denominator. For this reason, describing Clomid as having exactly one twin percentage is less accurate than describing the range of evidence and its context.

Gonadotropins and Multiple-Pregnancy Risk

Gonadotropins are injectable hormonal medications used to stimulate follicular development. Depending on the preparation, treatment can involve follicle-stimulating hormone, or FSH, and related gonadotropin activity.

Compared with oral agents, gonadotropin stimulation has often been associated with greater concern about multiple gestation because a stronger multifollicular ovarian response can occur.

The AMIGOS trial illustrates this clearly. Among ongoing pregnancies with fetal heart activity, the gonadotropin group had a 32% multiple-gestation rate, compared with 13% with letrozole and 9% with clomiphene. Importantly, the gonadotropin group included 24 twin and 10 triplet gestations, while all multiple gestations in the oral-medication groups were twins.

That does not establish a universal “32% gonadotropin twin rate.” The outcome was multiple gestation among a particular group of ongoing pregnancies in women with unexplained infertility, and some of those multiples were triplets.

Why Gonadotropin Stimulation Is Different

Gonadotropins act more directly on ovarian follicular development. When several follicles develop, more than one egg may have the potential to ovulate. This makes the resulting ovarian response especially important to the risk of multiple pregnancy.

Research comparing ovarian-stimulation strategies also shows that the apparent difference between gonadotropins and oral medications is influenced by the treatment protocol. A systematic review and individual-participant-data meta-analysis found a higher multiple-pregnancy rate with gonadotropins in the overall comparison with clomiphene and letrozole.

However, when investigators restricted analyses to studies using more conservative stimulation strategies or stricter cancellation practices, the difference in multiple pregnancy became statistically inconclusive.

This does not mean gonadotropin treatment has no multiple-pregnancy risk. It means the treatment label alone does not describe the whole risk. How treatment is administered and how ovarian response is managed also matter.

Twins vs Higher-Order Multiples

This distinction is especially important with gonadotropin research.

Twin pregnancy means two fetuses. Multiple gestation is a broader category and may include twins, triplets, or more.

A study reporting a 20% multiple-gestation rate is therefore not necessarily reporting a 20% twin rate. Before comparing a number across medications, the actual outcome being counted must be checked.

Why Follicle Number Matters

One of the most useful ways to understand fertility-medication twin risk is to look beyond the medication and focus on the number of mature follicles present during ovarian stimulation.

A large retrospective study evaluated more than 50,000 ovarian-stimulation IUI cycles and examined multiple-gestation risk according to age and mature follicle count.

Among women younger than 38 in that study, increasing the mature follicle count from one to five increased the clinical-pregnancy rate from 14.6% to 21.9%. But the multiple-gestation rate per treatment cycle increased much more sharply, from 0.6% to 6.5%.

Meanwhile, the singleton-pregnancy rate changed comparatively little, from 14.1% to 16.4%.

The finding illustrates an important concept: creating more follicles can increase the chance of pregnancy, but beyond a point much of the additional pregnancy rate may come from multiple pregnancies rather than additional singleton pregnancies.

These figures describe the study population and should not be used as personal treatment thresholds.

Monofollicular vs Multifollicular Response

A monofollicular response means one main follicle develops. A multifollicular response means more than one follicle develops to a stage considered relevant in the treatment or study.

Multifollicular response is important because several potentially ovulatory follicles create more opportunities for more than one egg to be fertilized.

That is why asking only, “Which fertility drug causes more twins?” misses an important part of the biology. A more useful question is:

How did the ovaries respond to that treatment in the population being studied?

How Age Modifies the Relationship

The relationship between follicle number and multiple gestation is not identical at every maternal age.

In the large follicle-count study, the rise in multiple gestation associated with additional mature follicles was particularly important in younger age groups, while the pattern differed in older participants.

This is one reason fertility-treatment statistics should not be separated from the characteristics of the study population. Maternal age can modify the relationship between ovarian response and pregnancy outcome.

How Monitoring and Treatment Protocol Affect Risk

Monitoring is one of the reasons a medication does not have a single protocol-independent twin rate.

During monitored fertility treatment, clinicians may use ultrasound and other clinical information to assess follicular development and ovarian response. The purpose is not simply to determine whether treatment is “working.” The response can also help clinicians evaluate the risk that more than one egg could be available for fertilization.

Why Ultrasound Monitoring Matters

Ultrasound can provide information about how many follicles are developing and how the ovaries are responding during a treatment cycle.

Two people who take the same medication can develop different numbers of follicles. Similarly, two clinical trials using the same drug may produce different multiple-pregnancy outcomes if their participants have different ovarian responses or if the treatment protocols handle multifollicular response differently.

Monitoring therefore provides important context between the medication and the eventual pregnancy outcome.

Why Study Protocol and Cancellation Criteria Matter

Clinical studies do not all use identical stimulation strategies or rules for responding to excessive follicular development.

Some protocols are more conservative about limiting multifollicular response. Others may differ in starting strategy, treatment adjustment, monitoring, or criteria for not proceeding with a cycle.

In the individual-participant-data meta-analysis of ovarian-stimulation strategies for unexplained infertility, differences in gonadotropin starting strategy and cancellation criteria helped explain variation between studies in multiple-pregnancy outcomes.

This matters for interpretation because a percentage reported from one protocol cannot automatically be treated as an intrinsic property of the medication itself.

Why Different Studies Report Different Twin-Risk Percentages

Apparently conflicting fertility-medication statistics often become much easier to understand once the details behind the percentages are compared.

Five differences matter especially.

Different Patient Populations

A study of people with PMOS, formerly PCOS, is not studying the same population as a trial of ovulatory women with unexplained infertility.

Underlying fertility diagnoses, baseline ovulatory function, age, and other clinical characteristics can affect treatment response and pregnancy outcomes.

This is why the 3.4% letrozole twin-pregnancy result from the PMOS/PCOS trial and the 13% letrozole multiple-gestation result from the AMIGOS unexplained-infertility trial should not be treated as two attempts to measure the same universal percentage.

Different Treatment Settings

Ovulation induction, ovarian stimulation, IUI-associated treatment, and assisted reproductive technologies represent different clinical contexts.

Even when the same medication name appears in two studies, the surrounding treatment process may be different.

A statistic is therefore most informative when the treatment setting is reported alongside it.

Different Denominators

This may be the most overlooked reason fertility statistics appear to disagree.

A study can calculate a percentage using:

• all participants enrolled;
• all treatment cycles;
• all conceptions;
• clinical pregnancies;
• ongoing pregnancies;
• or live-birth outcomes.

Those denominators answer different questions.

For example, “5% of treatment cycles resulted in twins” is not mathematically equivalent to “5% of pregnancies were twins.” The second percentage excludes all cycles that did not result in pregnancy.

Different Outcome Definitions

Studies may report:

• twin pregnancy;
• multiple pregnancy;
• multiple gestation;
• twin live birth;
• multiple birth;
• or higher-order multiple pregnancy.

These outcomes overlap, but they are not interchangeable.

A study that combines twins and triplets under “multiple gestation” cannot be converted into a twin rate without knowing how many of the multiples were actually twins.

Different Study Eras and Clinical Practices

Fertility care changes over time.

Monitoring practices, patient selection, stimulation strategies, and approaches to reducing multiple pregnancy can differ between older studies and contemporary practice.

The clomiphene literature demonstrates this particularly well. Older figures remain widely quoted, while modern systematic-review and large real-world cohort data produce somewhat different estimates.

The appropriate response is not to choose whichever number is lowest or highest. It is to identify what each number measures and whether it applies to the question being asked.

For a broader statistical overview, see our fertility medication and twin-rate statistics resource.

How to Read a Fertility-Medication Twin-Risk Statistic

Before comparing two percentages, ask three questions:

1. Who was studied?
2. What outcome was counted?
3. What was the denominator?

If a study reports…	The denominator may be…	What the figure answers
Twins per treatment cycle	All treated cycles	How often a treatment cycle resulted in a twin outcome
Twins among pregnancies	Pregnancies only	Among people who became pregnant, how many pregnancies were twins
Multiple gestation among ongoing pregnancies	Pregnancies reaching a defined ongoing stage	How many continuing pregnancies involved more than one fetus
Twin live births	Live-birth outcomes	How many live-birth outcomes involved twins

Per Cycle vs Per Pregnancy vs Per Live Birth

Imagine 100 treatment cycles lead to 20 pregnancies, and two of those pregnancies are twins.

The twin outcome would represent:

• 2% of all treatment cycles;
• but 10% of pregnancies.

Both percentages can be mathematically correct. They answer different questions.

This simple distinction explains why comparing fertility-study percentages without their denominators can produce misleading conclusions.

Relative Risk vs Absolute Risk

Absolute risk describes how often an outcome occurred in a group, such as 5 twin pregnancies among 100 pregnancies.

Relative risk compares the frequency of an outcome between groups. A risk can double in relative terms while the absolute increase remains much smaller.

For consumer interpretation, the absolute numbers are often especially useful because they show the scale of the outcome directly.

Numerical Difference vs Statistically Demonstrated Difference

Two treatment groups can have different observed percentages without the study establishing that the treatments genuinely differ in the wider population.

The large PMOS/PCOS letrozole-versus-clomiphene trial is a useful example. Twin pregnancy occurred in 3.4% of pregnancies in the letrozole group and 7.4% in the clomiphene group, but the difference was not statistically significant.

It is accurate to say that fewer twins were observed in the letrozole group in that trial. It is stronger, and not supported by that result alone, to say that the study proved letrozole cuts twin risk by more than half.

This type of distinction is part of how we interpret fertility-treatment evidence in the Odds of Twins methodology.

Twin Pregnancy vs Multiple Pregnancy

The terminology used in fertility research can materially change what a statistic means.

Twins, Triplets and Higher-Order Multiples

• Singleton pregnancy: one fetus.
• Twin pregnancy: two fetuses.
• Multiple gestation or multiple pregnancy: more than one fetus, including twins, triplets, or more.
• Higher-order multiples: usually triplets or more.
• Multiple birth: a birth outcome involving more than one baby, which is not identical to a multiple pregnancy measured earlier in gestation.

This distinction matters because pregnancy loss can occur between an early pregnancy measurement and live birth, and because some studies combine twins and higher-order multiples into one category.

Fraternal vs Identical Twins

Fertility medications most directly relate to the biological pathway that can produce dizygotic, or fraternal, twins.

Dizygotic twins occur when two separate eggs are fertilized. A treatment that results in multiple ovulation can therefore create the opportunity for fraternal twinning.

Monozygotic, or identical, twins arise when a single fertilized embryo divides. That is a biologically different process. Research has examined monozygotic twinning in fertility-treatment settings, but it should not be confused with the multiple-ovulation mechanism that explains much of the increased dizygotic-twin risk associated with ovarian stimulation.

What the Evidence Lets Us Conclude

• There is no universal fertility-medication twin percentage. A valid percentage needs a population, treatment setting, outcome definition, and denominator.
• Letrozole and clomiphene do not have a simple, universally established ranking for twin risk. Some PMOS/PCOS studies have observed fewer twins with letrozole, but major comparisons have not always found a statistically significant difference, and unexplained-infertility studies have produced different numerical patterns.
• Gonadotropin ovarian stimulation has generally raised greater concern about multiple gestation. The risk is closely related to multifollicular response and is influenced by treatment protocol and clinical management.
• Follicle number matters. Large studies show that increasing numbers of mature follicles can substantially increase multiple-gestation risk, particularly in younger populations, without a comparable increase in singleton pregnancy.
• Monitoring and protocol matter. The same drug used under different stimulation and cycle-management strategies may not produce the same observed multiple-pregnancy rate.
• A study result is not an individual’s prediction. Population statistics can explain patterns, but personal fertility-treatment decisions require individualized clinical assessment.

Frequently Asked Questions

Which fertility medication has the highest chance of twins?

There is no universal percentage that applies to every treatment protocol, but gonadotropin ovarian stimulation has generally been associated with greater multiple-pregnancy concern than oral agents such as letrozole and clomiphene. The actual risk is strongly affected by ovarian response, follicle number, monitoring, treatment protocol, and patient characteristics.

Does letrozole increase the chance of twins?

Twin pregnancies occur with letrozole fertility treatment, but there is no single letrozole twin rate that applies to everyone. A major PMOS/PCOS trial reported twins in 3.4% of resulting pregnancies in the letrozole group, while a separate unexplained-infertility trial reported a different multiple-gestation percentage in a different population and denominator.

Does Clomid increase the chance of twins?

Clomiphene citrate, or Clomid, is associated with a higher likelihood of multiple pregnancy than conception without fertility treatment. However, published estimates vary. Contemporary systematic-review and large cohort data generally produce lower figures than some of the older percentages that remain widely quoted.

Are twins more likely with Clomid or letrozole?

The answer depends on the population and study. In a large PMOS/PCOS trial, twin pregnancy was observed in 7.4% of clomiphene pregnancies and 3.4% of letrozole pregnancies, but that difference was not statistically significant. In a major trial of unexplained infertility, the numerical pattern was different, and letrozole again did not differ significantly from clomiphene in multiple gestation.

Why are multiple pregnancies more of a concern with gonadotropins?

Gonadotropins directly stimulate ovarian follicular development and can produce a multifollicular response. When several potentially ovulatory follicles develop, the opportunity for multiple eggs to be fertilized increases. The observed risk also depends on the stimulation and monitoring protocol.

Does having more follicles mean a higher chance of twins?

Research shows a strong relationship between increasing mature-follicle count and multiple-gestation risk during ovarian stimulation. More follicles do not guarantee twins, but they can increase the opportunity for multiple ovulation and multiple pregnancy.

Why do different sources give different fertility-drug twin percentages?

They may be studying different populations, different infertility diagnoses, different treatment protocols, different numbers of follicles, and different outcomes. They may also calculate the percentage per treatment cycle, per pregnancy, per ongoing pregnancy, or per live birth. Those figures cannot be compared as though they all measure the same thing.

Is a fertility-drug twin percentage usually calculated per treatment cycle or per pregnancy?

Either is possible. There is no single standard denominator used in every published result. Always check whether the percentage refers to treatment cycles, pregnancies, ongoing pregnancies, or live births before comparing it with another figure.

Can fertility medications cause identical twins?

Fertility medications most directly increase the opportunity for fraternal, or dizygotic, twins by increasing the possibility of multiple ovulation. Identical, or monozygotic, twins result from splitting of one embryo and involve a different biological mechanism. Fertility-treatment research has examined monozygotic twinning as well, but it should not be treated as the same process as medication-related multiple ovulation.

References and Evidence Notes

This article prioritizes professional guidance, randomized trials, systematic reviews, large cohort studies, and official drug information. Numerical findings are presented with their study context rather than being treated as universal individual probabilities.

1. American Society for Reproductive Medicine Practice Committee. Multiple Gestation Associated With Infertility Therapy: A Committee Opinion. Fertility and Sterility, 2022.
2. Diamond MP, et al. Letrozole, Gonadotropin, or Clomiphene for Unexplained Infertility. New England Journal of Medicine, 2015.
3. Legro RS, et al. Letrozole versus Clomiphene for Infertility in the Polycystic Ovary Syndrome. New England Journal of Medicine, 2014. The condition discussed in this historical study is now termed PMOS, formerly PCOS.
4. Danhof NA, et al. Ovarian Stimulation Strategies for Intrauterine Insemination in Couples With Unexplained Infertility: A Systematic Review and Individual Participant Data Meta-analysis. Human Reproduction Update, 2022.
5. Garthwaite H, Stewart J, Wilkes S. Multiple Pregnancy Rate in Patients Undergoing Treatment With Clomifene Citrate for WHO Group II Ovulatory Disorders: A Systematic Review. Human Fertility, 2022.
6. Impact of Clomiphene Citrate on Multiple Gestation Births and Perinatal Outcomes: A Nationwide Cohort Study. Fertility and Sterility, 2025.
7. Evans MB, et al. Mature Follicle Count and Multiple Gestation Risk Based on Patient Age in Intrauterine Insemination Cycles With Ovarian Stimulation. Obstetrics & Gynecology, 2020.
8. DailyMed. CLOMID (Clomiphene Citrate) Prescribing Information. U.S. National Library of Medicine.
9. International Evidence-based Guideline and participating professional organizations. Terminology update from Polycystic Ovary Syndrome (PCOS) to Polyendocrine Metabolic Ovarian Syndrome (PMOS), May 2026.

Scope note: This page explains population-level evidence about fertility medications and twin or multiple-pregnancy risk. It is not intended to recommend a medication, treatment dose, follicle threshold, or decision about whether an individual treatment cycle should proceed.