Polycystic Ovary Syndrome (PCOS) is a common endocrine disorder affecting women of reproductive age. It is characterized by a hormonal imbalance that leads to irregular menstrual cycles, signs of excess androgen hormones, and often the appearance of many small follicles on the ovaries. Because PCOS frequently results in anovulation—the failure to release an egg—it is a leading cause of infertility. This condition often requires medical intervention to achieve pregnancy, raising questions about whether PCOS increases the probability of having twins or other multiples. This article clarifies the relationship between PCOS, fertility treatments, and the likelihood of a multiple gestation.
PCOS and Unassisted Conception of Multiples
The natural occurrence of twins in the general population, without the aid of fertility treatments, is relatively low. When a woman with PCOS conceives without any medical intervention, her underlying risk of having twins is generally no different from a woman without the condition. The hormonal dysfunction associated with PCOS typically causes anovulation or highly irregular ovulation, which makes conception difficult.
The issue for women with PCOS is not that they are naturally prone to releasing multiple eggs, but rather that they may not release any egg consistently. If a woman with PCOS manages to ovulate and conceive naturally, her odds of a multiple birth remain near the baseline rate. Therefore, PCOS itself does not inherently predispose a person to a spontaneous twin pregnancy. The perceived connection between PCOS and twins stems almost entirely from the methods used to overcome the resulting infertility.
How Fertility Treatments Impact Twin Likelihood
The reason women with PCOS have a higher rate of multiple gestations is directly related to the pharmacological treatments used to stimulate the ovaries. These treatments are designed to induce ovulation, but they can sometimes overstimulate the ovaries. This process, known as hyperovulation, can lead to the release of two or more eggs in a single cycle, resulting in dizygotic, or fraternal, twins if multiple eggs are fertilized.
Oral Medications
Oral ovulation induction medications, such as clomiphene citrate (Clomid) and letrozole, are often the first line of treatment for anovulation caused by PCOS. These drugs work by encouraging the body to produce hormones that stimulate follicular development. With clomiphene, the chance of a twin pregnancy is generally cited to be in the range of 5% to 12%, which is significantly higher than the natural rate. Letrozole is sometimes preferred for women with PCOS because it may carry a slightly lower risk of multiples compared to clomiphene.
Injectable Gonadotropins
Injectable gonadotropins are more potent forms of hormone therapy and carry the highest risk for multiples, including triplets and higher-order gestations. These medications directly supply the hormones needed to stimulate multiple follicles to mature simultaneously. The twin pregnancy rate with gonadotropins can be as high as 30% in some populations. Because women with PCOS are highly sensitive to these hormones, treatment requires very careful monitoring with ultrasound to prevent the development of too many mature eggs.
In Vitro Fertilization (IVF)
IVF is a more controlled method, where the risk of multiples is managed by the number of embryos transferred into the uterus. In the past, transferring multiple embryos was common practice, resulting in a high rate of twins. Modern medical standards strongly favor a Single Embryo Transfer (SET) to minimize health risks. While transferring two embryos can increase the twin rate to approximately 40% in women under 35, a singleton pregnancy is the primary goal of most IVF cycles.
Health Considerations for Multiple Pregnancies
While the prospect of twins may seem appealing, the medical community works to minimize the risk of multiple births due to the associated health complications. A multiple gestation places a greater strain on the mother’s body compared to a singleton pregnancy. Maternal risks are more than doubled and include a higher likelihood of developing gestational hypertension, which can progress to preeclampsia, and gestational diabetes.
The mother is also at an increased risk for anemia, and delivery often involves a Cesarean section due to complications. For the infants, the primary concern is the high rate of preterm birth, with over 60% of twins being born before 37 weeks. Preterm birth frequently leads to low birth weight and a significantly higher chance of needing care in a neonatal intensive care unit (NICU).
Preterm infants are more vulnerable to developmental complications, including chronic breathing problems, intestinal issues, and a greater risk of cerebral palsy. The elevated risk of these complications is why reproductive endocrinologists use strategies like low-dose medication protocols and single embryo transfer during IVF. The medical aim is always to achieve a healthy, successful singleton pregnancy, even when treating infertility related to PCOS.