Ovarian hyperstimulation syndrome (OHSS) usually occurs as a result of taking gonadotropins — hormonal medications that stimulate the production of eggs in a woman's ovaries. These injectable fertility drugs may be prescribed to treat irregular ovulation or infertility. In ovarian hyperstimulation syndrome, your ovaries become swollen and painful.

About one-fourth of women who use gonadotropins get a mild form of ovarian hyperstimulation syndrome, which goes away after about a week. If you become pregnant after taking one of these fertility drugs, however, your symptoms of ovarian hyperstimulation syndrome may last several weeks. Fewer than 2 percent of women taking fertility drugs develop a more severe form of ovarian hyperstimulation syndrome, which can cause rapid weight gain, abdominal pain, vomiting and shortness of breath.

In most cases, the symptoms of OHSS begin three to 10 days after you take medications to stimulate ovulation. The severity of OHSS symptoms varies, and symptoms may worsen or improve over time.

Mild OHSS

• Mild to moderate abdominal pain that may come and go
• Abdominal bloating or increased girth
• Mild nausea
• Vomiting
• Diarrhea
• Tenderness in the area of your ovaries

More severe OHSS

• Rapid weight gain, such as an increase of 5 to 10 pounds in one to two days, or weight gain of more than 10 pounds in three or more days
• Severe abdominal pain
• Severe, persistent nausea and vomiting
• Decreased urinary frequency
• Dark urine
• Shortness of breath
• Tight or enlarged abdomen
• Dizziness

When to see a doctor
If you have any symptoms of ovarian hyperstimulation syndrome, tell your doctor. Even if you have a mild form of the syndrome, your doctor will want to observe you for weight gain or worsening symptoms. If your symptoms are severe, last longer than a week or get worse, seek medical attention.

Ovarian hyperstimulation syndrome develops after you take a type of fertility medication that acts directly on your ovaries, stimulating them to produce multiple eggs. This treatment, known as controlled ovarian stimulation, is more likely to cause symptoms of ovarian hyperstimulation than is the more common approach to inducing ovulation — treatment with clomiphene (Clomid, Serophene), a drug that acts on the pituitary gland.

The hormonal drugs most likely to cause OHSS are called gonadotropins. They may contain:

• Follicle-stimulating hormone (FSH), which stimulates the formation of multiple fluid-filled cysts (follicles) where eggs mature
• Luteinizing hormone (LH), which supports egg maturation and triggers ovulation
• Human menopausal gonadotropin (hMG), which has both LH and FSH
• Human chorionic gonadotropin (HCG), a stand-in for the LH surge that, in natural cycles, causes the follicle to release the egg

OHSS happens only after the follicle-stimulating phase of an ovulation-induction cycle, when you receive an injection of HCG to trigger ovulation. Typically, signs and symptoms appear within the first 10 days after the injection, when the ovarian blood vessels have an abnormal reaction to the hormone and begin to leak fluid. This fluid fills the follicles, swells the ovaries and sometimes moves into the abdomen in large amounts.

Some women develop OHSS during a pregnancy achieved following ovulation induction, as pregnancy itself causes a natural increase in HCG levels. Rare cases of OHSS have also occurred in pregnant women who conceived without ovulation induction.

Factors that increase the risk of developing OHSS include:

• Polycystic ovary syndrome — a common reproductive disorder that causes irregular menstrual periods, excess hair growth and abnormal findings on ultrasound examination of the ovaries
• Large number of follicles
• Young age
• Low body weight
• High or steeply increasing level of estradiol (estrogen) before an HCG shot
• Previous episodes of OHSS

Young women with polycystic ovary syndrome are at highest risk of ovarian hyperstimulation syndrome. But knowing these risk factors doesn't predict exactly who will get OHSS, and sometimes the syndrome affects women with no risk factors.

About 1 to 2 percent of women undergoing ovarian stimulation develop a severe form ovarian hyperstimulation syndrome. Complications of severe OHSS may include:

• Fluid collection in the abdomen (ascites) and sometimes the chest
• Electrolyte disturbances (sodium, potassium, others)
• Blood clots in large vessels, usually in the legs
• Kidney failure
• Twisting (torsion) of an ovary
• Rupture of a cyst in an ovary, which can lead to serious bleeding
• Breathing problems (adult respiratory distress syndrome)

Some of these complications may be life-threatening, but OHSS is unlikely to be fatal. Severe OHSS may increase the chance of pregnancy loss, either through miscarriage or termination because of complications.

The diagnosis of ovarian hyperstimulation syndrome is based on your symptoms rather than on any test. During treatment with fertility drugs, your doctor will regularly evaluate your ovaries with a vaginal ultrasound exam. This procedure uses sound waves to create an image of the inside of your ovaries. The ovarian follicles show up as dark, circular areas. If you have OHSS, the ultrasound may show that your ovaries are swollen, with several large fluid-filled cysts where the follicles developed.

Ovarian hyperstimulation syndrome usually goes away on its own within a week or two, or somewhat longer if you're pregnant. Treatment is aimed at keeping you comfortable, decreasing ovarian activity and avoiding complications.

Mild OHSS
For mild symptoms, follow these recommendations:

• To ease abdominal discomfort, take over-the-counter painkillers such as acetaminophen (Tylenol, others) or ibuprofen (Advil, Motrin, others).
• Avoid sexual intercourse, as it may be painful and can cause a cyst in your ovary to rupture.
• Weigh yourself on the same scale each day, and tell your doctor about any rapid or unusual weight gain.
• Call your doctor if your signs and symptoms get worse.

Moderate OHSS
If your symptoms worsen rapidly or last longer than a week, call your doctor. Follow the guidelines for mild OHSS in addition to the suggestions below.

Treatment for moderately severe OHSS may involve:

• Taking either anti-nausea medication or prescription painkillers or both
• Having frequent physical exams and ultrasound exams
• Weighing yourself each day and measuring your abdominal girth, noting any changes
• Measuring your urine output each day
• Seeing your doctor to get blood tests to monitor for dehydration, electrolyte imbalance and other problems
• Drinking large amounts of fluids, such as sports drinks containing electrolytes and a carbohydrate solution
• Draining excess fluid via a needle inserted in your abdominal cavity
• Staying as active as possible and wearing support stockings to help prevent blood clots

Severe OHSS
If you develop signs or symptoms of severe illness, you may need to be hospitalized for careful monitoring and more aggressive treatment, including intravenous (IV) fluids. Serious complications may require further treatments, such as surgery for a ruptured ovarian cyst or intensive care for liver or lung complications.

Most women who develop OHSS can continue their day-to-day routine. Light physical activity can be helpful, but avoid strenuous and high-impact activities and sexual intercourse. Bed rest isn't usually needed and may increase the risk of blood clots.

To lessen the chance that you'll develop ovarian hyperstimulation syndrome, your doctor will create an individualized plan for your fertility medications, taking into account any risk factors you have for OHSS. Your doctor will also carefully monitor each treatment cycle with frequent or daily ultrasound exams to view the development of follicles, and with blood tests to check your estradiol level.

Your doctor may use a variety of strategies to help prevent ovarian hyperstimulation syndrome:

• Adjusting medication dosage. Your doctor will use the lowest possible dose of gonadotropins to achieve the goals of stimulating your ovaries and triggering ovulation.
• Coasting. If your estradiol levels are high or a large number of follicles have developed, your doctor may stop your gonadotropin injections and wait a few days before giving HCG, which triggers ovulation. This is known as "coasting."
• Avoiding use of HCG. Because OHSS develops only after HCG is given, alternatives to HCG for triggering ovulation are being studied as a way to prevent OHSS. One option is a genetically engineered form of luteinizing hormone, but so far the high cost of this drug makes it impractical. Another option is to use gonadotropin-releasing hormone (Gn-RH) agonist instead of HCG to trigger ovulation.
• Canceling the ovulation induction or IVF cycle. If OHSS appears very likely, your doctor may decide not to administer HCG. This will prevent ovulation and OHSS, and you will not be able to conceive, but you'll still have to pay for the medications taken earlier in the cycle.
• Follicle aspiration and freezing all embryos. For women undergoing IVF, all the follicles (mature and immature) may be aspirated (removed) to reduce the chance of OHSS. The mature follicles are fertilized and frozen, and the ovaries are allowed to rest for one or two cycles. Then the desired number of embryos are thawed and transferred back to your uterus. This procedure slightly reduces the chance of pregnancy and costs more, but it almost eliminates the chance of OHSS.