Bma Illustrated Medical Dictionary

disorderssuch as haemophilia,cystic
fibrosis, and Tay–Sachs disease. Chemi-
cal analysis of amniotic fluid can help
to diagnose developmental abnorm-
alities such as spina bifida. Rhesus
incompatibilityand maturity of the fetal
lungs can also be checked.
Amniocentesis is usually performed in
the 14th–18th week of pregnancy. It
slightly increases the risk of miscarriage
or early rupture of the membranesand is
therefore recommended only when the
fetus is thought to be at increased risk
of an abnormality. (See also antenatal
care, chorionic villus sampling.)
amnionOne of the membranes that
surrounds the fetusin the uterus. The
outside of the amnion is covered by
another membrane called the chorion.
amniotic fluidThe clear, watery fluid
(popularly called the “waters”) that sur-
rounds the fetusin the uterus. The fluid
is contained within the amniotic sac. It
cushions the fetus, allowing movement.
Amniotic fluid is produced by cells lin-
ing the amniotic sac and is constantly
circulated. It appears in the 1st week
after conception and gradually in-
creases in volume until the 10th week,
when the increase becomes very rapid.

Occasionally, excessive fluid is formed

(see polyhydramnios); less frequently,

insufficient amniotic fluid is formed

(see oligohydramnios).

amniotic sacThe membranous bag that

surrounds the fetusand is filled with

amniotic fluidas pregnancy advances.

The sac is made up of 2 membranes, the

inner amnionand the outer chorion.

amniotomyArtificial rupture of the am-

niotic membranes (breaking the “waters”)

performed for induction of labour.

amoebaA type of protozoon (see proto-

zoa). An amoeba is a microscopic

single-celled organism with an irregular,

changeable shape. Amoebae live in

moist environments, such as fresh

water and soil. Some types of amoebae

are parasites of humans, causing dis-

eases such as amoebiasis.

amoebiasisAn infection caused by the

amoeba ENTAMOEBA HISTOLYTICA, a tiny

single-celled parasite that lives in the

human large intestine. Amoebiasis is

spread through drinking water or eating

food contaminated by human excreta

containing cysts of the amoeba.

Some people carry the amoeba in their

intestines and excrete cysts but have no

symptoms. However, some strains in-

vade and ulcerate the intestinal wall,

causing diarrhoea and abdominal pain,

which may develop into full-blown

dysentery. The amoebae may spread via

the bloodstream to the liver, or, rarely,

the brain or lung, where they cause

abscesses. Symptoms of an amoebic

liver abscess are chills, fever, weight

loss, and painful enlargement of the liver.

Treatment of all forms of amoebiasis

is with drugs such as metronidazoleor

diloxanide, which kill the parasite with-

in a few weeks, leading to full recovery.

amoebic dysenterySee amoebiasis.

amoebicidesA group of drugs used to

treat amoebiasis. Examples are dilox-

anide, and metronidazole.

amoxapineAn antidepressant drug re-

lated to the tricyclics. Possible adverse

effects include blurred vision, dizziness,

drowsiness, abnormal muscular move-

ments, menstrual irregularities, and

breast enlargement.

amoxicillinA penicillin drugcommonly

used to treat a variety of infections,

AMNION AMOXICILLIN

A

Ultrasound

beam

Ultrasound

probe

Bladder

Amniotic

fluid

Syringe

Fetus

Cervix

Uterus Placenta

AMNIOCENTESIS