One of the 2 membranes that surround the embryo. The chorion lies outside the amnion, has small fingerlike projections called the chorionic villi, and develops into the placenta.
This is the more external of the two fetal membranes. (See PLACENTA.)
n. the embryonic membrane that totally surrounds the embryo from the time of implantation. It is formed from *trophoblast lined with mesoderm and becomes closely associated with the *allantois. The blood vessels (supplied by the allantois) are concentrated in the region of the chorion that is attached to the wall of the uterus and forms the *placenta. See also villus. —chorionic adj.
A glycoprotein hormone secreted by the PLACENTA in early pregnancy, and stimulating the CORPUS LUTEUM within the ovary (see OVARIES) to secrete OESTROGENS, PROGESTERONE, and relaxin. The hormone is essential for the maintenance of pregnancy up to about 6–8 weeks of gestation. A RADIOIMMUNOASSAY can be used to detect its presence, and pregnancy can be diagnosed as early as six days after conception by testing for it in the urine. Some tumours also secrete human chorionic gonadotrophin, particularly HYDATIDIFORM MOLE, which produces large amounts.... human chorionic gonadotrophin
A method of diagnosing genetic abnormalities in a fetus using a small sample of tissue taken from the chorionic villi at edge of the placenta. Because the cells have the same chromosome makeup as those in the fetus, they can be used to detect genetic abnormalities. Chorionic villus sampling (CVS) is usually performed in the first 3 months of pregnancy in women who are at a higher-than-normal risk of having a child with a chromosomal disorder, such as Down’s syndrome, or a genetic disease, such as thalassaemia. Chromosome analysis of the villi cells takes place in the laboratory. CVS slightly increases the risk of miscarriage. choroid A layer of tissue at the back of the eye, behind the retina. The choroid contains many blood vessels that supply nutrients and oxygen to the retinal cells and to surrounding tissues in the eye. choroiditis Inflammation of the choroid. It is often caused by infections such as toxocariasis or toxoplasmosis, more rarely by sarcoidosis, syphilis, and histoplasmosis. It sometimes has no obvious cause. Treatment includes corticosteroid drugs for the inflammation, and antibiotic drugs for any causative infection.... chorionic villus sampling
A hormone produced by the placenta in early pregnancy. Human chorionic gonadotrophin (HCG) stimulates the ovaries to produce oestrogen and progesterone, which are needed for a healthy pregnancy. HCG is excreted in the urine, and its presence in urine is the basis of pregnancy tests on urine samples. ... gonadotrophin, human chorionic
the number of chorionic membranes present on direct examination of the placenta and membranes following delivery of *twins. Chorionicity can be determined antenatally by ultrasound, ideally between 10 and 14 weeks gestation. Where two placental masses are identified, the pregnancy is dichorionic. More frequently a single placental mass exists and chorionicity can only be determined by evaluation of the intertwin membrane; the pregnancy is monochorionic when the fetuses share a chorion (see illustration; see also lambda sign; T-sign). Chorionicity rather than zygosity is a better determinant of perinatal outcome in twins. The perinatal mortality rate of monochorionic pregnancies may be up to four times that of dichorionic.... chorionicity
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