Medical Glossary: O

Obstetrician

A physician who specializes in obstetrics. Obstetricians are concerned with the care of the mother and fetus during pregnancy, childbirth and the immediate postpartum period as well as the physiologic and pathologic function of the female reproductive tract.

Occipito Anterior

A term used to describe the position of the baby in the uterus prior to entering labor. Also known as Anterior Position, it describes the baby when its head is facing forward towards the front of the mother.

Occipito Posterior

A term used to describe the position of the baby in the uterus prior to entering labor. Also known as Posterior Position, it describes the baby when its head is facing backward towards the mother's back.

Oligohydramnios

A term used to describe a lack of or insufficient amniotic fluid within the amniotic sac.

Omphalocele

A congenital birth defect in which internal abdominal organs protrude outside the body through the umbilicus. It is usually closed surgically soon after birth.

Oocyte

A term used to describe the egg that is released from the ovary during each ovulation. Medically it refers to an incompletely developed (unfertilized) ovum.

Opiates

A soporific or narcotic drug that is made from opium or its derivatives or by synthetic means. Sometimes called opioids.

Opioids

A soporific or narcotic drug that is made from opium or its derivatives or by synthetic means. Sometimes called opiates.

Organogenesis

A term used in embryology to describe the period between two weeks and eight weeks of gestation when the baby experiences rapid growth in organ and organ systems development.

During this period the baby is extremely vulnerable to environmental hazards and toxic substances and any interference with the sequential processes may result in congenital abnormalities.

Os

Derived from the latin for bone, in obstetrics the term is used to describe the opening of the cervix.

Ossicles

A collective term used to describe some of the small bones that make up the inner ear.

Ossification

A term used to describe the development and hardening of bone. There are two processes: intramembranous ossification and intracartilaginous ossification.

Intramembranous ossification takes place in the formation and development of the skull and involves initially creating membrane which subsequently harden to become bone.

Intracartilaginous ossification is the formation of rods of cartilage, which subsequently harden to form the bones of limbs.

Ovarian Cycle

The regular production of hormones by the ovary in response to hormonal stimulus from the brain. The ovarian cycle controls and regulates the endometrial cycle.

Ovary

Part of the female reproductive system, it is one of a pair of female gonads located on each side of the lower abdomen. Similar in size and shape to an almond, at ovulation an egg is extruded from a follicle on the ovary's surface. The mature follicle secretes both estrogen and progesterone to regulate the menstrual cycle.

Oviduct

Also called the fallopian tubes, it is one of a pair of ducts that lead from the peritoneal cavity over the ovary to the uterus. The tubes serve to lead the ovum to the uterus and the spermatozoa to the ovaries. The oviducts are located in the lower abdomen by a broad ligament called the mesosalpinx.

Ovulation

The release of an egg from a woman's ovaries each month.

Ovulatory Age

The age of the fetus as determined from the date of conception, usually 266 days. The ovulatory age of the fetus is usually about two weeks younger than the gestational age. Also called the fertilization age.

Ovum

A specialized sexual cell, commonly called the egg or egg cell, of the female, which corresponds to the sperm in males. It is larger than the sperm because of the food material which is contained in it, and it lacks a tail, instead having a smooth round surface.

The ovum was discovered by K.E. von Baer and are produced in the female ovaries. Like the sperm, the number of chromosomes are halved before fertilization in a process called meiosis.

Once fertilized, the single cell consisting of half the chromosomes of each of the ovum and the sperm is known as the fertilized ovum, or egg.

Oxygenate

A process which involves combining, treating or saturating with oxygen. It usually refers to the oxygenation of the bloodstream.

Oxytocin

A pregnancy hormone that both stimulates breast milk production and stimulates uterine contractions. Synthetic oxytocins have been created to induce labor.

Oxytocin Challenge Test

A test designed to determine whether a fetus is ready for labor and delivery. A diluted concentration of oxytocin is administered in order to stimulate uterine contractions lasting approximately 30 - 40 seconds, three times within a ten minute period. The baby's heart rate is monitored for fetal distress. While beneficial, additional tests are recommended prior to performing emergency cesarean section or inducing labor.

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