Aim-To determine whether those most easily reviewed in a population prevalence study diVer from those followed up only with diYculty. Methods-All babies born before 32 weeks of gestation in the North of England in 1983, 1990, and 1991 were traced, and all the survivors assessed at two years by one of two independent clinicians. Results-818 of the 1138 live born babies survived to discharge. There was some non-significant, excess disability in the 5% of long term survivors who were diYcult to trace because of social mobility, but eight times as much severe disability in the 1% (9/796) in care and in the 5% (38/796) whose parents initially failed to keep a series of home or hospital appointments for interview, and five times as much emergent disability in the 2.7% (22/ 818) who died after discharge but before their second birthday. Had the babies who were seen without diYculty been considered representative of all the babies surviving to discharge, the reported disability rate would have been two thirds what it really was (6.9% instead of 11.0%). Conclusions-Population prevalence studies that ignore those who seem reluctant to cooperate risk serious ascertainment bias. (Arch Dis Child Fetal Neonatal Ed 1998;79:F83-F87)

Gestation, if accurately assessed, can give a woman facing very preterm delivery a clear indication of the prognosis for her baby and help her judge the appropriateness of accepting obstetric intervention and sustained perinatal support.

Compared with mainstream classmates, children who are born extremely early continue to have higher levels of parent- and teacher-reported emotional, attentional, and peer problems well into their teens. However, despite these problems, they do not show signs of more serious conduct disorders, delinquency, drug use, or depression.

Objective To obtain unbiased estimates of the variation of birthweight with gestation in infants born Setting The former Northern Regional Health Authority.Design Information on birthweight was collected during a collaborative study of every registered and unregistered birth at 22 to 31 weeks of gestation in the region in 1983 and 1990 to 1991. These birthweights were then related to computer-generated Tyneside norms for all registered births at 28 to 42 weeks of gestation between 1984 and 1991. Some local information was also collected on fetal weight after termination of pregnancy on social grounds at 16 to 21 weeks of gestation.Results Weight centiles constructed after excluding infants with a gross, externally visible, malformation and those dying before the onset of labour suggest that previously published European standards have overestimated birthweight in infants < 28 weeks of gestation, some low centiles being 30% in error. Female and first-born infants weighed 4% less than their male and later-born counterparts at all gestations studied. A single correction factor can therefore be used to correct for sex and parity, eliminating the need for separate centile graphs. Twin pregnancy was associated with a 10% reduction in mean birthweight in pregnancies lasting < 37 weeks, and this difference increased progressively in pregnancies lasting longer than this. ConclusionThe small number of low birthweight infants in previous datasets and the selective exclusion of all nonregistered births have made previous second trimester weight-for-gestation norms unreliable.before 32 weeks of gestation. INTRODUCTIONBecause only 1 % of infants are born before 32 weeks of gestation, few such infants have been included in most studies of the variation of birthweight with gestation. While some North American studies have tried to provide normative data for such infants'-4, most European studies have avoided this challenge5-*. Furthermore, many of the published studies relate to the experience of a single institution9-13, and most of the population based studies have reported only on infants classified as li~eborn'~-'~, which could bias the birthweight distribution especially for infants born in the second trimester of pregnancy. In the UK two most frequently used weight standards for infants born before 32 weeksI2J5 derive from hospital-based samples that included only 80 and 97 live births at 24 to 27 weeks of gestation, respectively. New weight standards have now been constructed from two geographically-defined cohort studies that involved the collection of carefully validated information on all the nonmalformed registered and unregistered singleton births that occurred at 22 to Correspondence:Royal Victoria Infirmary, Newcastle upon Tyne NE 1 4LP, UK.Dr U. K. Wariyar, Consultant Paediatrician, 31 weeks of gestation in 1983 and 1990 to 1991 to mothers normally resident in the Northern Region. There were 1524 infants in this sample after the exlusion of those known to have died before the onset of labour. These data have then...

Objective: To ascertain the health and school performance of teenagers born before 29 weeks gestation (extremely low gestational age (ELGA)) and to compare those in mainstream school with classroom controls. Methods: Three geographically defined cohorts of babies born in 1983 and 1984 were traced at the age of 15-16 years. Their health, abilities, and educational performance were ascertained using postal questionnaires to the teenagers themselves, their parents, their general practitioners, and the teachers of those in mainstream school. Identical questionnaires were sent to classroom controls. Results: Of the 218 teenagers surviving to the age of 16 years, information was obtained on 179. Of these, 29 were in special schools and 150 in mainstream school, 10 of whom had severe motor or sensory impairment. Using the Child Health Questionnaire, parents of teenagers in mainstream school reported a higher incidence of problems than controls in physical functioning (difference in mean scores 9.0 (95% confidence interval (CI) 4.9 to 13.1)) and family life (difference in mean scores for family cohesion 7.0 (95% CI 1.6 to 12.4)). In all areas of learning, teachers rated the ability of the ELGA teenagers in mainstream school lower than the control group. Parents of teenagers in special schools reported a higher rate of problems in most areas. Conclusions: One in six ELGA survivors at age 16 years have severe disabilities and are in special schools. Most ELGA survivors are in mainstream school and are coping well as they enter adult life, although some will continue to need additional health, educational, and social services.