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Assisted Reproductive Techniques
Assisted reproductive techniques (ARTs) involve manipulation of sperm and ova in vitro with the goal of producing an embryo.
ARTs may result in multifetal pregnancy, but risk is much less than that with controlled ovarian hyperstimulation. If risk of genetic defects is high, the embryo can often be tested for defects before transfer and implantation (preimplantation genetic diagnosis).
In women < 35, > 47% of ART cycles result in pregnancy, and 87% of the pregnancies end in live births in the US (2010 data). The pregnancy rate decreases with increasing age; for women aged 41 to 42, the pregnancy rate is about 20%, and only about 62% of these pregnancies end in live births. Use of donor oocytes is usually recommended for women > 42.
IVF can be used to treat infertility due to oligospermia, sperm antibodies, tubal dysfunction, or endometriosis as well as unexplained infertility. The procedure involves the following:
Controlled ovarian hyperstimulation: Clomiphene plus gonadotropins or gonadotropins alone can be used. A gonadotropin-releasing hormone (GnRH) agonist or antagonist is often given to prevent premature ovulation. After sufficient follicular growth, human chorionic gonadotropin (hCG) is given to induce final follicular maturation and ovulation.
Oocyte retrieval: About 34 h after hCG is given, oocytes are retrieved by direct needle puncture of the follicle, usually transvaginally with ultrasound guidance or less commonly laparoscopically.
Fertilization: The oocytes are inseminated in vitro. The semen sample is typically washed several times with tissue culture medium and concentrated for motile sperm, which are then added.
Embryo culture: After sperm are added, the oocytes are cultured for about 2 to 5 days.
Embryo transfer: Only 1 or a few of the resulting embryos are transferred to the uterine cavity, minimizing the chance of a multifetal pregnancy, the greatest risk of IVF. The number of embryos transferred is determined by the woman’s age and likelihood of response to IVF. Other embryos may be frozen in liquid nitrogen for transfer in a subsequent cycle.
Birth defects may be more common after IVF, but experts are uncertain whether the increased risk is due to IVF or to factors contributing to infertility; infertility itself increases risk of birth defects. Still, as of mid-2012, the overwhelming majority of the > 5 million children born after IVF have no birth defects.
GIFT is an alternative to IVF but is used infrequently, typically for women with unexplained infertility or with normal tubal function plus endometriosis. Multiple oocytes and sperm are obtained as for IVF but are transferred—transvaginally with ultrasound guidance or laparoscopically—to the distal fallopian tubes, where fertilization occurs. Live birth rates per cycle are about 25 to 35% at most infertility centers.
This technique is useful when other techniques are not successful or are unlikely to be so or when a severe sperm disorder is present. Oocytes are obtained as for IVF. A single sperm is injected into each oocyte to avoid fertilization by abnormal sperm. The embryo is then cultured and transferred as for IVF. In 2010, about two thirds of all ART cycles in the US involved intracytoplasmic sperm injection. Risk of birth defects may be increased after intracytoplasmic sperm injection, possibly because the procedure itself can damage the sperm, egg, or embryo or because sperm from men who have mutations of the Y chromosome are used. Most reported birth defects involve the male reproductive tract.
A combination of IVF and GIFT, zygote intrafallopian tube transfer, use of donor oocytes, and transfer of frozen embryos to a surrogate mother are sometimes used. Some of these techniques raise moral and ethical issues (eg, rightful parentage in surrogate motherhood, selective reduction of the number of implanted embryos if multifetal pregnancy results).
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