Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders affecting women of reproductive age, with an estimated prevalence of 8–13% depending on diagnostic criteria. While PCOS is primarily known for its metabolic and hormonal disruptions—such as hyperandrogenism, insulin resistance, and irregular menstrual cycles—it is also a leading cause of anovulatory infertility. Fortunately, fertility treatments ranging from ovulation-inducing medications to advanced reproductive technologies have enabled countless women with PCOS to conceive. However, these same treatments carry a well-documented but often underappreciated risk: the increased likelihood of multiple pregnancies. This article provides a comprehensive examination of the risks associated with multiple pregnancies in the context of PCOS treatments, covering definitions, mechanisms, maternal and fetal complications, management strategies, and long-term implications. By understanding these risks, patients and providers can make informed decisions that balance the desire for pregnancy with the imperative of safety.

What Are Multiple Pregnancies?

A multiple pregnancy is defined as a gestation involving more than one fetus. The most common forms are twins (dizygotic or monozygotic), followed by triplets, quadruplets, and higher-order multiples. The incidence of multiple pregnancies has risen markedly over the past few decades, largely due to the increased use of assisted reproductive technologies (ART) and ovulation induction. In natural conception, twins occur in roughly 1–2% of pregnancies, whereas in women undergoing fertility treatments, the rate can exceed 20–30% depending on the protocol.

Dizygotic (fraternal) twins result from the fertilization of two separate eggs by two separate sperm; they are more common with ovulation-inducing drugs that stimulate the release of multiple eggs. Monozygotic (identical) twins arise from a single fertilized egg that later splits; although not directly linked to ovarian stimulation, some studies suggest that ART may slightly increase the rate of monozygotic twinning. Higher-order multiples (triplets or more) occur most frequently when multiple embryos are transferred or when the ovaries release several eggs simultaneously.

Why PCOS Treatments Increase the Risk of Multiple Pregnancies

The fundamental reason PCOS treatments elevate the risk of multiples lies in their mechanism of action. Many fertility medications used for ovulation induction work by stimulating the ovaries to produce one or more mature follicles. In women with PCOS, the baseline follicular pool is often larger, and the response to stimulation can be exuberant, leading to the release of multiple eggs. The key treatments and their associated risks are outlined below.

Ovulation Induction Agents

Clomiphene citrate is a selective estrogen receptor modulator that increases gonadotropin release, promoting follicle development. Twin rates with clomiphene range from 5–10%, with higher-order multiples occurring in less than 1% of cycles. Letrozole, an aromatase inhibitor, has gained popularity because it may result in a lower rate of multiples compared to clomiphene—typically around 3–4% for twins—while achieving comparable ovulation and pregnancy rates. Despite this advantage, letrozole still carries an elevated risk compared to natural conception.

Gonadotropins (injectable FSH or hMG) are the most potent ovulation induction agents and carry the highest risk of multiple pregnancy. Twin rates can exceed 20%, and the risk of triplets or more can reach 5–10% unless meticulous monitoring and dose adjustments are employed. Because PCOS patients tend to be very sensitive to gonadotropins, they are especially prone to excessive follicular development.

In Vitro Fertilization (IVF)

IVF bypasses the fallopian tubes and involves the retrieval of eggs, fertilization in a laboratory, and transfer of embryos into the uterus. The risk of multiple pregnancy in IVF is largely determined by the number of embryos transferred. Historically, transferring two or more embryos was common, leading to high multiple-pregnancy rates (30–40% or more). Modern practice, driven by professional guidelines from the American Society for Reproductive Medicine (ASRM) and the Society for Reproductive Technology (SART), strongly advocates for elective single embryo transfer (eSET) in good-prognosis patients, including many with PCOS. When eSET is used, the multiple-pregnancy rate falls to less than 5%.

However, PCOS patients often have high numbers of eggs retrieved and may produce multiple good-quality embryos. This can tempt patients and providers to transfer more than one embryo to increase the immediate chance of pregnancy, especially in the absence of comprehensive counseling about the risks of multiples.

Risks Associated with Multiple Pregnancies for the Mother

Multiple pregnancies impose significant physiological demands on the maternal body. Compared to singleton pregnancies, mothers carrying twins, triplets, or more face substantially elevated risks across a range of complications.

Preeclampsia and Hypertensive Disorders

Preeclampsia—a syndrome of high blood pressure, proteinuria, and often multisystem organ dysfunction—occurs two to three times more frequently in twin pregnancies than in singletons. In triplet and higher-order gestations, the risk can be as high as 40%. Preeclampsia can lead to serious complications including eclampsia (seizures), stroke, placental abruption, and the need for preterm delivery. Women with PCOS already have a higher baseline risk for hypertensive disorders related to insulin resistance and vascular dysfunction; multiple pregnancy further amplifies this danger.

Gestational Diabetes Mellitus (GDM)

Multiple pregnancies increase the risk of GDM due to elevated placental hormones that antagonize insulin action. The risk is roughly 1.5–2 times higher than in singleton pregnancies. PCOS itself is a strong risk factor for GDM because of pre-existing insulin resistance. Thus, the combination of PCOS and a multiple pregnancy can substantially raise the likelihood of GDM, which in turn carries its own risks for the mother (preeclampsia, progression to type 2 diabetes) and the fetus (macrosomia, birth trauma, neonatal hypoglycemia).

Placental Abnormalities

Multiple pregnancies are associated with higher rates of placenta previa (covering the cervical os), placental abruption (premature separation), and placental insufficiency. These conditions can cause life-threatening hemorrhage, preterm birth, and fetal growth restriction. Additionally, the risk of postpartum hemorrhage is elevated due to the larger placental mass and uterine overdistension.

Other Maternal Complications

  • Anemia: Increased blood volume demands often lead to iron-deficiency anemia.
  • Preterm labor and cervical insufficiency: The uterus is stretched beyond its normal capacity.
  • Cesarean delivery: The rate of C-section is markedly higher with multiples, and with it the risks of infection, thromboembolism, and surgical complications.
  • Postpartum depression: The physical and emotional demands of caring for multiple newborns contribute to higher rates of mood disorders.
  • Mortality: Though rare in developed countries, maternal mortality is increased in multiple pregnancies due to hemorrhage, hypertensive crises, and thromboembolism.

Risks to the Fetus and Neonate

Multiple pregnancies pose serious threats to the developing fetuses and newborns. Fetal risks are magnified in higher-order multiples, largely driven by prematurity and growth disorders.

Preterm Birth

Preterm birth—delivery before 37 weeks of gestation—is the most common and consequential complication of multiple pregnancies. The average gestational length for twins is 35 weeks, for triplets 32 weeks, and for quadruplets 29 weeks. Very preterm (<32 weeks) and extremely preterm (<28 weeks) infants are at risk for long-term neurodevelopmental disabilities, respiratory problems, and gastrointestinal complications such as necrotizing enterocolitis. PCOS in itself has not been consistently linked to spontaneous preterm birth, but the high rate of iatrogenic preterm delivery (due to maternal complications) further compounds the risk.

Low Birth Weight and Intrauterine Growth Restriction

Multiple fetuses compete for placental space and nutrients, leading to increased rates of low birth weight (<2500 g) and very low birth weight (<1500 g). Discordant growth—where one twin grows significantly smaller than the other—is especially dangerous and may require earlier delivery. Growth restriction in utero can have lifelong consequences for cardiovascular and metabolic health.

Congenital Anomalies

Multiple pregnancies have a slightly increased risk of structural anomalies, particularly neural tube defects and cardiac defects. Part of this increase may be due to the underlying fertility treatments rather than the multiplicity itself, but the total risk remains modest.

Perinatal Mortality and Morbidity

The perinatal mortality rate for twins is two to five times higher than for singletons; for triplets, it is even higher. Major causes include very preterm delivery, growth restriction, and complications of monochorionic placentation (e.g., twin-to-twin transfusion syndrome in monozygotic twins).

Managing the Risk of Multiple Pregnancies in PCOS Treatment

Preventing multiple pregnancies begins with careful patient selection, counseling, and protocol optimization. While no strategy can eliminate the risk entirely, the following evidence-based measures significantly reduce the incidence and severity of multiples.

Ovulation Induction: Monitoring and Dose Titration

For women undergoing oral ovulation induction with clomiphene or letrozole, the starting dose should be the lowest effective dose. Serial transvaginal ultrasound monitoring is essential to track the number and size of developing follicles. Most protocols recommend cancelling the cycle if more than two to three mature follicles are present, particularly when using gonadotropins. When gonadotropins are required (for example, in women who do not respond to oral agents), a low-dose step-up protocol should be used to minimize excessive follicular growth. ASRM guidelines provide detailed recommendations for monitoring and cancellation thresholds.

IVF: Single Embryo Transfer

Elective single embryo transfer (eSET) is the single most effective intervention for reducing multiple gestations in IVF. In good-prognosis patients, including most PCOS patients with a eupoloid embryo, eSET yields pregnancy rates that are only slightly lower than double-embryo transfer while virtually eliminating the risk of twins. Professional societies, including the Society for Assisted Reproductive Technology, strongly advocate for eSET in patients under 35 with favorable prognosis. For women with PCOS who produce multiple embryos, cryopreservation of surplus embryos gives them the opportunity for additional transfer cycles without increasing multiple risk.

Preconception and Lifestyle Optimization

Optimizing maternal health before treatment can improve outcomes and reduce complications should a multiple pregnancy occur. Key measures include:

  • Weight management: Achieving a healthy BMI (preferably <30) reduces the risk of hypertensive disorders and GDM.
  • Insulin resistance management: Metformin therapy has been shown to reduce the risk of ovarian hyperstimulation syndrome and may lower GDM risk, though its role in preventing multiples is indirect.
  • Nutrient supplementation: High-dose folic acid (1–4 mg) is recommended before conception to reduce neural tube defects, which are more common with multiples.

Medical Management of Established Multiple Pregnancy

Once a multiple pregnancy is diagnosed, the focus shifts to reducing harms. Women should receive specialized prenatal care with more frequent monitoring—including serial cervical length assessments, blood pressure checks, and glucose tolerance testing—and be educated about warning signs of preterm labor. In higher-order multiples (triplets or more), multifetal pregnancy reduction (purposeful reduction of the number of fetuses to twins or a singleton) can be offered as an option to improve outcomes. This is a deeply personal decision and requires comprehensive counseling from a maternal-fetal medicine specialist.

Emotional, Financial, and Long-Term Considerations

Beyond the physical risks, multiple pregnancies impose substantial emotional and financial burdens on families. The cost of neonatal intensive care for preterm multiples can be staggering, and many parents face prolonged stress related to caring for two or more infants simultaneously. Multiple births are also associated with higher rates of marital discord and postpartum mental health struggles. Long-term developmental follow-up is often needed for children born preterm or growth-restricted. These considerations underscore the importance of shared decision-making early in the treatment process.

Conclusion

Polycystic ovary syndrome is a highly treatable cause of infertility, but the very treatments that enable conception can inadvertently increase the risk of multiple pregnancies. The consequences of multiple gestations—for mothers and infants alike—are serious and often preventable. By employing careful monitoring during ovulation induction, embracing single embryo transfer in IVF, and providing comprehensive preconception counseling, healthcare providers can dramatically lower the incidence of multiples. Patients, for their part, should be empowered with accurate information about these risks and actively participate in treatment decisions. With a thoughtful, individualized approach, the goal of a healthy singleton pregnancy can be achieved while minimizing the potential harms of multiple gestation.