Pregnancy Terms Glossary
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Bacterial vaginosis (BV)

Bag of waters

The membrane (amnion) surrounding the fetus and the amniotic fluid.

Banana Sign

Curvature of the cerebellum (the part of the brain that controls balance) around the midbrain giving the cerebellum the shape of a banana. Caused by Arnold-Chiari II malformation.  In 95% percent of cases the Arnold-Chiari II malformation is accompanied by hydrocephalus and myelomeningocele (open spina bifida).

Basal Body Temperature

The body temperature measured in the morning before moving about or eating after at least 6 hours of sleep.

Bicornuate uterus

Two separate single horn uterine bodies sharing one cervix.

The uterine tubes, uterus, and upper vagina are formed by fusion of the two paramesonephric (Müllerian) ducts beginning at about 10 weeks gestation. Fusion of the ducts with resorption of the uterine septum is usually completed by about 20 weeks' . Partial failure of the ducts to unite results in two separate single horn uterine bodies sharing one cervix.

Bicornuate uterus is associated with increased risk for miscarriage, preterm labor, breech presentation, and fetal growth restriction.

Bikini incision. See Pfannenstiel's incision


Bilirubin is a yellowish pigment produced from the breakdown of hemoglobin the protein that carries oxygen in the red blood cells). Bilirubin is removed from the body largely by the liver. The liver of many newborns may not be mature enough to remove bilirubin from the blood stream quickly enough. The excess bilirubin may build up giving the the infant's skin and membranes a yellow color a condition called jaundice.

Biophysical profile (BPP)

A prenatal test that uses the findings of the  nonstress test (NST)  and activities of the baby during an ultrasound examination to check on the well being of  baby. A score of 2 is given for each component present. A score of 8 or greater is reassuring.
Component  Score 2 Score 0
Non-stress Test Two or more fetal heart rate accelerations of at least 15 beats/min and lasting at least 15 seconds during  20 minutes of observation No accelerations or less than two accelerations of fetal heart rate in 20 minutes
Breathing At least one episode of fetal breathing lasting 30 seconds during a 30 minute period of observation. (Hiccups are included as breathing activity) Less than 30 seconds of fetal breathing movements in 30 min
Movement 2 or more discrete gross body/limb movements in 30 minutes, simultaneous limb and trunk movements Less than 2 gross body/limb movements in 30 minutes
Tone At least one episode of motion of a limb from position of flexion to extension and rapid return to flexion (opening and closing of hand considered normal tone) Position of semi or full limb extension with no return or slow return to flexion with movement; absence of fetal movement
Amniotic fluid volume At least 1 pocket of fluid that measures at least 2 cm in two perpendicular planes Largest pocket of amniotic fluid measures < 2 cm in two perpendicular planes


Bishop score

An assessment of the likelihood of successful induction of labor. The Bishop score assigns points for cervical dilatation, effacement, consistency, cervical position, and the station of the presenting part. A Bishop's score of 6or les  indicates low probability of successful induction. Other scoring systems exist.



0 1 2
Dilation (cm)
1-2 cm
Effacement (%)
Position Posterior Mid Anterior




+1, +2 



The rapidly dividing fertilized egg when it enters the uterus

Blighted Ovum

A fertilized egg that has failed to develop.

Blood Pressure

Bloody show

Passage of blood-tinged mucus from the vagina caused by loss of the cervical mucous plug. Bloody show often precedes the onset of labor.

Body Mass Index (BMI)

The body mass index (BMI) is a measure of someone's weight in relation to their height. The BMI is used to estimate the amount of body fat a person has. The BMI is calculated either as:

BMI = (Weight in pounds /  Height in inches 2 ) x 703

BMI = (Weight in kilograms  / Height in meters 2)


Short disproportionately wide head. Brachycephaly is seen with several disorders including Down syndrome and syndromes associated with premature closure of the coronal suture (Apert, Crouzon, Pfeiffer, Saethre-Chotzen and Carpenters).

Bradley Method (husband-coached birth)

A method of natural childbirth developed by Robert A. Bradley, M.D. (1917–98). The Bradley method emphasizes education and relaxation techniques for pain management. The method prepares the baby's father to be the mother's birth coach, and prepares the mother to deliver without pain medication.


In a fetus a mean heart rate less than 110 beats per minute lasting for at least two minutes. In an adult a sustained heart rate less than 60 beats per minute.

Braxton Hicks Contractions

Sporadic uterine contraction that do not increase in intensity and do not result in childbirth, typically felt after 20 weeks. Named after John Braxton Hicks a British gynecologist who first described these contractions in 1872.

Breech presentation

The baby is in a sitting position with the buttocks, knees, or feet nearest to the cervix.

Breech presentation occurs in 25 percent of pregnancies less than 28 weeks' and 1 to 3 percent of births at term. The three types of breech presentation are frank breech (flexed at hips with extended knees-legs above buttocks), footling breech (one or both hips extended-leg(s) extended below buttocks), and complete breech (flexed hips and knees-no limbs extended).


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