Prematurity is defined as a baby born before 37 weeks from the first day of the last menstrual period. Very low birth weight babies are those that weigh less than 1.5kg, whilst extremely low birth weight babies weigh less than 1.0kg.
Small babies face two problems, one is prematurity which means being unready for the extra-uterine world. The other is being small for dates which are classed as intra uterine growth retardation. The former is often reluctant to feed and needs much encouragement whilst the latter has been starved and has a voracious appetite. However, it is not uncommon for babies to be both early and to have suffered intra uterine growth retardation.
About 7 to 10% of babies are born before 37 weeks gestation. There are racial differences in normal birth weight so that if the parameter of weight alone is taken there may be babies of Indian race who are wrongly labelled whilst being full term and healthy. About 7% of babies in the UK weigh less than 2.5kg at birth, rising to 10% in deprived areas.
Simply labelling all babies born before 37 weeks as premature fails to illustrate the marked gradation in terms of severity of the problem with increasing prematurity. A baby born at 36 weeks will probably be a little slow to feed. A baby born before 33 weeks will have more serious problems including, possibly, immature lungs. Birth before 28 weeks causes very significant problems but the survival rate of babies born before 28 weeks is quite remarkable nowadays.
There are a number of possible causes for early delivery.
1. Induction or Caesarean section may have been undertaken because of serious adverse intrauterine conditions. This may include pre-eclampsia or an abrupted placenta. The decision that has to be made is to consider the circumstances and the maturity of the baby and to ask, "Is the baby safer in or out?" This is a matter of balancing risks.
2. Multiple pregnancies often leads to premature labour and this may be very early if multiple means more than twins.
3. Cervical incompetence is one of progressively earlier labours in successive pregnancies with premature rupture of membranes and a painless early dilation of the cervix.
4. Low socio-economic status, inadequate or absent antenatal care and poor maternal nutrition all predispose to premature labour. Smoking and excessive alcohol consumption are also risk factors.
5. Heroin withdrawal or too rapid reduction of methadone during the last trimester can induce premature labour. Drug abusers must be encouraged to comply closely with their regimen and reduction of methadone should be slow in the last trimester. Cocaine can also cause premature labour. It is a potent vasoconstrictor and this can have a devastating effect on placental function.
6. Small babies are more likely with a mother under 17 or over 35 years old.
7. Bacterial vaginosis predisposes to premature labour.
A premature baby will look small and unprepared for this world. A baby who is also small for dates may have little subcutaneous fat and their skin may appear wrinkled. Premature babies face a number of problems that may be accentuated if there is intra uterine growth retardation too.
1. Hypothermia is a great risk, especially if there is little subcutaneous fat. A premature baby is less able to shiver and to maintain their body temperature.
2. Hypoglycaemia is also a risk, especially if small for dates. There may also be hypocalcaemia. Both can cause convulsions that may produce long term brain damage.
3. The more premature the baby, the greater the risk of respiratory distress syndrome. Steroids before delivery may reduce the risk but it is still very real. If the baby requires oxygen it must be monitored very carefully as if the levels are too high the premature baby is susceptible to retrolental fibroplasias and blindness.
4. The premature baby is also more susceptible to neonatal jaundice than a more mature baby.
5. They are susceptible to infection and to necrotising enteritis, which is inflammation of the intestine (especially the small intestine); usually characterized by diarrhoea.
6. They are susceptible to intraventricular brain haemorrhage with serious long term effects.
These are all problems faced by the neonatologist in a Special Care Baby Unit but when the baby is eventually discharged from hospital and goes home, that is not the end of problems.
The baby who is just slightly premature will probably have little or no long term problems but those who are very premature and who have a difficult start to life often suffer many more long term problems.
Support for parents
When a baby is in SCBU it is a very emotional and traumatic time for both the parents, not just the mother. They should be encouraged to visit and stay with the baby as much as possible. Breast feeding may be rather difficult but it should be encouraged, since breast milk is the best food for any baby but especially premature babies.
If the baby is attached to monitors and has tubes in and out of the body, it may not be possible to hold the baby or it may not be possible to do so for long. This should be encouraged as much as is compatible with the safety of the baby but bonding is much more difficult than with a normal, healthy, full term baby.
Whilst trying to keep a positive attitude, parents must also come to terms with the fact that their baby may not survive. There may also be difficult decisions about switching off ventilators and the expected quality of life if the child survives. It is difficult for parents to take in what they are told at such an emotional time. Therefore they may wish to discuss matters with their family doctor who is outside the hospital but who understands the issues involved.
Long term problems of premature babies
Figures about outcomes for premature babies have to be interpreted with a degree of caution. Different studies use different criteria for the degree of prematurity for inclusion. What is quite clear is that the more premature a baby might be, the greater the risk of death and the greater the risk of handicap in those who survive. There is a gradation of risk. Being both premature and light for dates would seem to add further to the risk.
Sight and hearing
Severe problems such as cerebral palsy, blindness and deafness may affect as many as 10 to 15% of significantly premature babies. About 1 in 4 babies with birth weight below 1.5kg has peripheral or central hearing impairment or both.
Birth weight below 1.5kg, gestational age of less than 33 weeks and Retinopathy of prematurity (ROP) are all risk factors for developing treatable refractive errors and Strabismus. At present there is no formal policy on follow up. In England and Wales in 2001, there were about 7500 live births fewer than 1500 g who needed screening for ROP, many on several occasions. Although most extremely preterm babies develop some degree of ROP, severe disease is relatively rare.
Follow up to school
Researchers have been watching the development of all babies in the UK who were born at least 15 weeks before term (25 weeks gestation or less) during the first 10 months of 1995. Of those 308 children who survived, 241 underwent formal psychological assessment using standard cognitive, language, phonetic and speech tests, with teachers rating their school achievement.
Of those children 40% were found to have moderate to severe learning difficulties and boys were twice as likely to be adversely affected as girls. The rates of severe, moderate, and mild disability were 22%, 24%, and 34%, respectively.
Disabling cerebral palsy occurred in 30 children representing 12%. Among children with severe disability at 30 months of age, 86% still had moderate-to-severe disability at 6 years of age. In contrast, other disabilities at the age of 30 months were poorly predictive of developmental problems at 6 years of age. Hence it seems that improvement may occur but it is less likely with greater severity.
Another study has suggested that children who were very premature may deteriorate rather than improve. They compared children at the age of 8 and 15 and found that full IQ dropped from an average of 104 to 95 and that the number needing extra educational provision rose from 15 to 24%. These were the same children assessed at 8 and 15 and so it does not represent better neonatal care in the younger ones.
Results indicate that between the ages of 8 and 15 years there is an apparent deterioration in neurodevelopmental outcome category, cognitive function, and extra educational support. It is not clear whether this represents a genuine deterioration in neurocognitive function or whether it represents the expression of pre-existing cerebral pathology in an increasingly complex environment.
Behavioural and Psychomotor problems
A study from Liverpool has looked at children of 7 and 8 who were born before 32 weeks and who were well enough to attend mainstream school. They were compared with full-term children of similar age in their class at school. Disabilities can be subtle and numerous and so a range of tests was used. The preterm children had a higher incidence of motor impairment, and this affected how well they did at school even when their intelligence was normal.
Over 30% had developmental coordination disorder (DCD) compared with 6% of classmates. The preterm children were significantly more likely be overactive, easily distractible, impulsive, disorganized and lacking in persistence, and to overestimate their ability. Attention deficit hyperactivity disorder (ADHD) was found in 8.9% of the preterm children and 2% of controls.
The children who had been the most premature were not necessarily those with the lowest scores. Although major disabilities have been reduced, the levels of disability tested here did not seem lower than those found in children born 10 or 20 years earlier, despite changes in care of the newborn.
IUGR may be very important in terms of early growth of the brain leading to poor IQ and developmental skills. Individuals who were born before 33 weeks gestation continue to show noticeable decrements in brain volumes and striking increases in lateral ventricular volume into adolescence.
Emotional development, teens and beyond
A study of teenagers in mainstream schools who were born before 29 weeks gestation showed that compared with mainstream classmates, they have higher levels of parent and teacher reported emotional, attentional, and peer problems well into their teens. Despite these problems, they do not show signs of more serious conduct disorders, delinquency, drug use, or depression.
A study of 18 and 19 years olds who were born before 33 weeks gestation showed that they had different personalities from controls with increased neuroticism and decreased extraversion scores. This was more marked in females than males.
Study of pre-term children who had reached 19 to 22 years of age showed that they were, on average, shorter than their contemporaries, more likely to use prescription medicines and less likely to have attended higher education.
The safest place for a child to develop is in utero and so it is important to try to prevent premature labour or such complications that very early delivery is indicated. There may be times when the intrauterine environment is so adverse that the baby is safer out than in. Antenatal care is important. Problems of social deprivation, poor maternal nutrition and substance abuse must all be addressed. Smoking should cease and alcohol consumption should be kept very much in moderation and there may be no safe lower limit. If cervical incompetence is suspected a Shirodkar suture has been the treatment since about 1948.
Information taken from www.patient.co.uk