As there is no conclusive genetic test for BWS at this time, a diagnosis for BWS can and should be made, not on blood tests, but rather based on a good history and clinical evaluation by a geneticist.

The BWS diagnosis is reached if there is a clinical suspicion AND presence of 2 of the 5 major characteristics.

These 5 major characteristics are:
1.    Macroglossia (large tongue)
2.    Unexplained Hypoglycemia in the first four months of life.
3.    Ear Creases or Pits
4.    Abdominal Wall Defect (including even a mild naval hernia)
5.    Birth weight over the 90-95% (adjusted for prematurity if relevant)

Although the other not so common characteristics may help with the diagnosis.

Macroglossia (enlarged tongue)
Although always larger than usual for an infant, the size of the tongue can vary from child to child, as can it's effects on the child's ability to eat, breathe, or speak. Therapy may be required, and in more severe cases, tongue reduction surgery may be necessary. In the past it was thought that most children seem to "grow into their tongues," but what often happens is that the lower jaw is pushed forward and becomes malformed as the result of constant pressure from the large tongue. Click here for more information.

Abdominal Wall Defects
-Omphalocele: a defect in the abdominal wall, near the umbilical cord, which allows some or all of the intestines and possibly other abdominal organs to protrude into a covering membrane (sac). This usually requires surgical intervention soon after birth.
-Umbilical Hernia: a hernia in the area of the navel, which may or may not require surgery.
-Diastasis Recti: weak or separated abdominal muscles

Over Growth
-Birth Weight and Length: usually above average.
-Visceromegaly: enlarged abdominal organs, particularly kidneys, liver, and pancreas.
-Hemihypertrophy: enlargement of one part of the body. Usually all or part of one side of the body is affected, but there are some cases where parts of both sides of the body are involved. Sometimes hemihypertrophy is not present at birth but becomes apparent later in childhood.

Associated facial features
-Earlobe creases : or pits behind the upper ear.
-Prominent occiput: enlarged back of the skull.
-Nevus Flammeus: a strawberry mark commonly found on the forehead and eyelids. This is sometimes called a "stork bite," and usually disappears in early childhood.

Full list of characteristics associated with BWS:

Noticed at birth or shortly thereafter:
Macroglossia (large tongue)
Abdominal wall anomalies (umbilical hernia, omphalocele, distasis recti)
Facial nevus flammeus (stork bites)
Visceromegaly (enlarged liver, kidneys, spleen, etc.)
Natal and post natal gigantism
Advanced bone age
Ear anomalies (pits, creases, notches, etc.)
Somatic asymmetry (may develop later as well)
Undescended testes
Clitoral hypertrophy (also called cliteromegaly)
Diaphragmatic abnormalities (eventration, hernia)
Muscular hypertrophy
Prominent occiput
Microcephaly
Neonatal hypoglycemia
Secondary polycythemia
Pancreatic hypertrophy, hyperplasia of the Islets of Langerhans
Cytomegaly and cysts of the adrenal cortex
Nephromegaly with prominent lobulations

May develop later:
Medullary dysplasia
Medullary sponge kidney
Kidney stones
Maxillary underdevelopment (midface hypoplasia)
Prognathism of lower jaw
Hearing loss (conductive and neurosensory)
Enlarged tonsils and adenoids
Scoliosis (due to asymmetry)
Wilms tumor
Hepatablastoma
Neuroblastoma
Nephroblastomatosis
Adrenal tumors
Pancreatoblastoma