Common Side Effects of the HCG Trigger Shot

HCG, or human chorionic gonadotropin, is a drug given to mature eggs from artificially stimulated ovaries during assisted reproductive technology, or ART procedures. HCG is usually given 34 to 36 hours before egg retrieval, since release usually occurs naturally 36-plus hours after administration, the University of Maryland Medical Center explains. HCG can be given as a recombinant, or laboratory-made drug, or in an injection derived from the urine of pregnant women. HCG in either form can have side effects.

Woman with headache holding her head (Image: David De Lossy/Photodisc/Getty Images)

Common Side Effects

Some side effects of HCG are mild and common. These include headache, irritability, sore breasts, mild fluid retention and weight gain, and depression. While these symptoms are usually short-lived, worsening symptoms should be reported to your doctor, as they could be early signs of ovarian hyperstimulation syndrome. Soreness at the injection site may occur; redness or swelling should be reported to your doctor.

Allergic Reactions

As with any drug, allergic reactions can occur to the proteins in HCG. These include rashes, hives, swelling, shortness of breath, lightheadness or collapse. Report any potential signs of allergy to your doctor immediately.

Ovarian Hyperstimulation

The most serious side effect of HCG when given to induce egg release in fertility procedures is the development of ovarian hyperstimulation syndrome, or OHSS. Ovarian hyperstimulation occurs when large number of follicles are matured after HCG is given. Some fertility clinics will not give HCG in an ART cycle if the estradiol level is over a certain number, to prevent OHSS from developing. Others will not transfer embryos if OHSS is present, because pregnancy will drive hormone levels even higher.

Side effects of mild OHSS include mild swelling, abdominal discomfort and weight gain. More serious side effects of OHSS include fluid third spacing, which means fluid is pulled out of the circulatory system and concentrated in tissues, causing massive swelling; possible organ failure from lack of perfusion due to decreased blood volume; and problems with blood clots due to blood being overly concentrated, according to third-year Harvard medical student S. Monica Soni and Gillian Lieberman, MD, of Harvard Medical School. Fluid may accumulate in the lungs, making breathing difficult. Nausea, vomiting and diarrhea may deplete already dry blood volume. OHSS can be fatal in rare cases, the U.S. National Library of Medicine states.

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