PURPOSE

PURPOSE

Babies who weigh 1.5 kg or less at birth are classified as very low birth weight (VLBW) babies. Only a few babies, 1.5 per cent, are born this tiny.¹

Babies with a very low birth weight look very different in comparison to babies with a healthy birth weight. Their heads appear much bigger than the rest of their bodies and they often look extremely fit with little body fat. The blood vessels can easily be seen through their transparent skin.

The main cause of low birth weight is preterm birth. This is when the baby is born early, usually before 30 weeks of pregnancy. This means the baby has less time to grow inside the mother and gain weight.  Much of a baby's weight is gained in the last stages of pregnancy.

A secondary cause of low birth weight is intrauterine growth restriction (IUGR). Many things can cause IUGR such as; problems with the placenta, birth defects or the mother's health. These things cause the baby to not grow properly during pregnancy. Babies who have IUGR and a very low birth weight are usually born prematurely and are physically very small.²

As well as being born prematurely, there are a range of other factors that can cause very low birth weight in babies. These include³:

- Race: African-American babies are twice as likely to have VLBW as white babies.

- Age: Mothers who are younger than age 17 or older than age 35 have a much higher risk of having a baby with VLBW.

- Multiple Births: Mothers who give birth to multiple babies at a time usually give birth prematurely     and so they have VLBW. About 10% of twins and more than one-third of triplets have very low birth weight.

- Mother's Health: Very low birth weight is common in babies whose mothers were exposed to drugs,   alcohol and cigarettes during pregnancy. Mothers who have poorer pregnancy nutrition - such as         mothers of lower socioeconomic status are also likely to have babies with very low birth weight.

Birth weight is related to the survival of VLBW babies. Survival data for infants born at UCSF from 1998-2002 (inclusive) are⁴:

Birth Weight (g)                                            Survival

500 - 750                                                          74%

751 - 1,000                                                       82%

1,000 - 1,250                                                    92%

1,250 - 1,500                                                    95%

The data set provided contains the following information. Pneumothorax is when air or gas collects around the lung. This cause the lung to collapse. This occurs when the air sacks in the babies lung bursts leaking air between the lung and the chest wall.This happens mostly in premature babies. The air sacks in the babies' lungs burst due to being too stretched by the air pressure.

Variables which can be used;

bwt                                 birthweight (g)
Low pH                          lowest pH in the first 4 days of life
pitct                                platelet count (thousands platelets per micro litre of blood)
ethinicity                        european or non-European
gest                                 weeks of gestation before birth
birthplace                       hospital or other
twin                                twin or single birth

meth                               mother treated with beta-methasone pre-birth
toc                                  tocolysis - mother treated with beta-adrenergic drug pre-birth
delivery                          caesarian or natural birth
vent                                assisted ventilation used on baby post-birth
pneumo                          pneumothorax occurred (baby's lung collapsed post-birth
pda                                 patent ductus artesiosus (a congenital heart defect) detected on baby
cld                                  chronic lung disease (baby on supplementary oxygen at 30 days)
sex                                  male or female
survival                           yes or no

The data set and following information came from a database recording VLBW babies born in America in the 1980s.

The purpose of this investigation is to determine whether there is a distinct difference between the birthweight of VLBW babies that survive and babies that do not survive. It is known the babies with VLBW are less likely to survive. This report will determine whether there is a clear relationship between the birth weight of VLBW babies that survive and those that don't. Obstrecians, doctors, midwives and expecting couples would all be interested in the information discovered in this investigation as they would all like to l<now the likelihood of survival of their child if that child has VLBW.

Because of this I suspect that the birth-weight of VLBW babies born has a direct correlation to their survival. If the birth-weight of these babies is lower, the chance of survival will also be lower than if the birth-weight was higher.

After examining the variables given in the data set it has been decided to investigate the birth weight of VLBW babies, comparing between those that survive and those that do not. This variable appears to give the strongest distinction between both of the groups.