Dictionary

NEW – fully searchable glossary in the Members Area – click here

A-C | D-F | G-I | J-L | M-O | P-R | S-U | V-Z |

In the following definitions, references to other dictionary entries are underlined; within the definitions, modifications of the defined term or alternative terms are given in bold, as are other glossary entries that do not provide additional information in the particular context; subheadings or emphasized words are in italics.

vacuum curettage Curettage in which the contents of the early pregnant uterus are sucked out using a soft plastic catheter. Used in the treatment of miscarriage, in the treatment of hydatidiform mole, and to induce abortion.

value judgment A philosophical device for moving from what is to what ought. It bridges what philosophers call the naturalistic fallacy -- but not with the approval of some career philosophers.

values See ethics.

varicocele A varicose vein in the scrotum, which in some cases can increase the temperature of the testis, causing oligospermia; more common on the left side than on the right (because the left testicular vein is longer and more likely to have incompetent valves). One of the few treatable causes of male infertility (the treatment is to tie off the vein), although not all sperm counts improve. There's more on varicocele, underwear design and avoiding saunas in WebPage 10.

vas deferens The long duct that transports sperm cells (spermatozoa) from the epididymis to the seminal vesicles. Can be missing from birth (congenital absence of the vasa deferentia) or blocked as a result of infection or intentional interruption (vasectomy). Plural: vasa deferentia.

vascular endothelial growth factor (VEGF) A growth factor (or local hormone) needed for new blood vessels to form in, for example, the corpus luteum, as it turns into an efficient hormone-producing gland making and releasing progesterone about a week after ovulation. Because such new blood vessels are rather leaky, excess VEGF from multiple corpora lutea during ovulation induction or superovulation using gonadotropins can be associated with new blood vessels trying to form in the general peritoneal cavity, leakage of fluid from which causes fluid to build up in the abdomen, a potentially dangerous condition known as the ovarian hyperstimulation syndrome. VEGF is also important in the formation of the placenta, so mutations of VEGF or its target proteins can cause recurrent miscarriage.

vasectomy Sterilization operation in a man involving surgical interruption of each vas deferens in the upper part of the scrotum. See also vasovasostomy (for vasectomy reversal).

vasectomy-reversal See vasovasostomy.

vasovasostomy Vasectomy reversal, the operation for reversing a sterilization operation (a vasectomy) in a man involving removal of the blocked part of each vas deferens, in the upper part of the scrotum, and joining by microsurgery one cut end or the vas to the other cut end. Generally not as successful at returning fertility as the equivalent operation in women (tubal anastomosis): the development of sperm antibodies increases with the length of time since sterilization and limits the effective sperm count after the reversal. Many clinics now carry out cryostorage of some sperm obtained at vasectomy reversal so that if pregnancy does not happen, or azoospermia persists, in vitro fertilization (IVF) can be carried out with ICSI without requiring a later operation (for MESA) on the man. MESA with ICSI and IVF can be used as an alternative to vasovasostomy.

VDRL See serological test for syphilis.

VEGF See vascular endothelial growth factor.

villus Plural: villi. See .

NEW – fully searchable glossary in the Members Area – click here

Wasserman reaction (WR) See serological test for syphilis.

Wilson's disease See serum copper.

Wolffian duct The mesonephric duct.

WR See serological test for syphilis.

NEW – fully searchable glossary in the Members Area – click here

yolk sac A sac-like structure attached to the under-surface of the developing embryo. The first part of the embryo to become visible on transvaginal ultrasound after the gestational sac, but not by itself as reassuring as seeing a beating fetal heart that the pregnancy will most likely avoid miscarriage. Not as important for a human embryo's nutrition as it is for a fertilized egg incubated by a hen, and in mammals contains no yolk, but the yolk sac’s lumen is continuous with the lumen of the embryo’s developing gut, or intestine, and shares an absorptive function. Cells from the yolk sac become incorporated into the fetus in many ways, including forming the germ primitive cells.

NEW – fully searchable glossary in the Members Area – click here

ZIFT See zygote intrafallopian transfer.

Zoladex See goserelin.

zona pellucida The tough but glassy-looking membrane that starts to surround the egg (the primary oocyte) while it’s still in the follicle, protects it against sperm which have not undergone the acrosome reaction at its surface, and keeps the cells of the early embryo together until the embryo, as a blastocyst, hatches through it in preparation for implantation.

zygote Fertilized egg or ovum up to the first cleavage division; this stage of development of the embryo takes about 22 hours, and for the last few of these hours it’s at the pronuclear stage. See also pronucleus.

zygote intrafallopian transfer (ZIFT) A form of assisted conception in which in vitro fertilization (IVF) is used to produce fertilization; transfer is made on the day after egg retrieval and IVF, before the fertilized egg divides (it’s at the zygote, or pronuclear stage). Useful if the potential fertilizing ability of sperm is in doubt. The transfer is made to the fallopian tube to obtain advantages similar to gamete intrafallopian transfer (GIFT) and is made possible by laparoscopy (with anesthesia) or by transvaginal ultrasound (without anesthesia). Synonymous with pronuclear-stage transfer (PROST).