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Method of Anesthesia May Matter for Fertilization Rates

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by Leigh Ann Woodruff, April 6, 2016

In the majority of cases, when a woman's eggs are retrieved during in vitro fertilization, she receives anesthesia. This may take the form of general anesthesia or conscious sedation in which patients are sedated, but they are able to respond to stimuli such as verbal questioning.

Interestingly, a new retrospective study by Argentinean scientists compared fertilization rates among nearly 450 patients who had undergone either general anesthesia or conscious sedation during egg retrieval and found significantly higher rates of fertilization and embryo development among those who received general anesthesia. However, there were no differences in pregnancy rates.

The findings were presented at the 2012 World Congress of Anesthesia.

"The study is interesting, but we should be cautious not to over-interpret the findings of a retrospective trial," says Alan Copperman, M.D., medical director of Reproductive Medicine Associates of New York. "There are numerous possible confounding variables."

Of the women the Argentinean scientists looked at, 105 received general anesthesia with midazolam and propofol, and 333 received conscious sedation with midazolam and dextropropoxyphene along with either dipyrone or ibuprofen. Among those who received general anesthesia, the doctors successfully fertilized 85 percent of the eggs were fertilized. For those in the conscious sedation group, the doctors successfully fertilized 81 percent. In addition, there were differences in embryo development among the two groups — 49 percent of the fertilized embryos from women who received general anesthesia developed into embryos five days following fertilization, compared with 45 percent of the fertilized eggs from the women who received conscious sedation.

But the type of sedation did not appear to have any effect on whether successful pregnancy and live birth was achieved. Approximately 50 percent of patients in both groups became pregnant, and 44 percent in the had successful deliveries.

"If the success rate isn’t different then the study is not clinically significant," Dr. Copperman says.

The researchers say the study suggests that drugs used in conscious sedation may cause an adverse effect that general anesthetics don't. They hypothesize that conscious sedation agents impair the accumulation of substances in the eggs cytoplasm and affect subsequent embryonic development.

"I am not sure that the hypothesis that anesthetic agents accumulate inside the oocyte and interfere with embryonic development is even biologically plausible," says Dr. Copperman.

Dr. Copperman points out that when you are discussing sedation, "there is a spectrum between 'conscious sedation — now more commonly called 'procedural sedation,' in which the patient remains aware of his or her person, surroundings, and conditions but without experiencing pain or anxiety — and 'general anesthesia,' a state of unconsciousness with the absence of pain sensation over the entire body.

"We definitely do not require an endotracheal tube and a respirator for this brief and safe procedure," he continues. "We have board certified anesthesiologists performing anesthesia for all egg retrievals."

If you are preparing for an egg retrieval, here are some questions you may want to ask your fertility doctor about anesthesia:

  • What level of anesthesia will I be receiving, and what is the definition of that level? (Some terms used are minimal sedation, moderate/conscious sedation, deep sedation/analgesic, general anesthesia)
  • What drugs will be used?
  • Who will be providing my anesthesia?
  • Who will be monitoring my anesthesia, and will that person be there the whole time?
  • What is my personal risk with this type of anesthesia?
  • When should I quit eating and drinking before the egg retrieval procedure?

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