Prenatal factors cause the majority of cerebral palsy cases.  Pre-term birth and low birth weight increase the risk dramatically.  Evidence suggests that five percent of newborns that weigh less than 3.5 pounds will develop cerebral palsy.  Children who survive birth but who are born before week 33 are up to 30 times more likely to have cerebral palsy than a baby born at term.

The younger the individual and the lower the birth weight, the more vulnerable that individual is.  Compared to a full-term baby of more than five pounds, an infant weighing less than three pounds is twice as likely to develop cerebral palsy.  The risk increases sharply for infants with extremely low birth weight.  They are 100 times more likely to develop cerebral palsy than a full-term infant.

There has been an increase of cerebral palsy cases among pre-term births over the last 30 years, but it may be occurring because a greater percentage of pre-term infants with damaged brains are now surviving.  Pre-term infants are far more vulnerable to the external, non-natal environment than full-term infants.  To survive, pre-term infants must quickly adjust to their new environment.

Some studies suggest that between early gestational age and lowered birth weight, there is an even greater risk of cerebral palsy for those that are younger than for those that are lighter.  “However, birth weight is dependent on both gestational age at delivery and the rate of intrauterine growth; therefore, these two risk factors must be studied independently of each other to separate their effects.  Nevertheless, because birth weight can be measured more accurately and is more widely available than gestational age, it has long been used as a surrogate for maturity."  (Alberman, Blair, and Stanley)

Hemorrhages within the blood vessels of the brain can result in cerebral palsy.  The highest percentage of hemorrhages occurs in babies with the youngest gestational age or birth weight.  The hemorrhages can combine with other factors to cause cerebral palsy, but the bleeding alone can result in the condition.

There are several kinds of cerebral palsy, and certain types are associated with premature birth.  It has been suggested that spastic diplegia may cause premature birth by impairing growth and development of an embryo.  Spastic diplegia has increased over the last 30 years as premature infant care has improved.  "While 24.8 percent of all children with cerebral palsy were born before 33 weeks gestation, over 40 percent of those with spastic diplegia were born before 33 weeks, compared with 25.2 percent with spastic hemiplegia, 15.6 percent with quadriplegia and 4.8 percent with other types of cerebral palsy. Therefore very pre-term infants are at particular risk of specific patterns of cerebral palsy."  (Alberman, Blair, and Stanley)

One common intervention used by obstetricians to prevent early delivery is the intravenous administration of magnesium sulfate.  Magnesium, an essential ingredient for physiological and neurological health, is necessary to prevent premature labor and high blood pressure.  This intervention has reduced the incidence of low birth weight, thus resulting in fewer cases of cerebral palsy.

Bachrach, Steven J., and Miller, Freeman.  Cerebral Palsy: A Complete Guide for Caregiving.  Baltimore: The Johns Hopkins University Press, 1995.

Hart, Hilary M., ed.  Clinics in Developmental Medicine.  London:  Mac Keith Press.   Alberman, Eva; Blair, Eve; and Stanley, Fiona.  Cerebral Palsies: Epidemiology and Causal Pathways.  London:  Cambridge University Press, 2000.  (The book is part of a series of hardcover monographs published by Mac Keith Press.  Four new ones are published each year.  The distributor is Cambridge University Press.)