Collection and use of routine maternity data

Analysis by gestational age of cerebral palsy in singleton births in north-east England 1970-94

We report from a well-established cerebral palsy (CP) register the changes in CP rates by gestational age for singleton births over a 25-year period in north-east England. The gestational ages of numerators and denominators are of high accuracy back to 1970 because academic units in paediatrics and obstetrics were studying the assessment of gestational age in individual infants, and the distribution of gestational age across all births in the north-east from the 1960s. The rate of CP rose between 1970-75 and 1990-94 from 1.6 to 2.3 per 1000 singleton neonatal survivors, a rise of 0.7/1000 [95% CI 0.2, 1.3]. There was little change in the rate of CP in term infants whereas in preterm infants (<37 weeks) it rose from 5.5 to 16.8, a rise of 11.3/1000 [95% CI 5.9, 16.8]. Rises occurred in the three preterm gestational age bands <28, 28-31, 32-36 weeks with the most marked rise in those <28 weeks from 0 to 112.7. The proportion of all cases of CP arising in the preterm group rose from 19% to 45%; and the proportion of the severest cases arising in the preterm group rose from 8% to 55%. In those born after 32 weeks, there is a preponderance of small-for-gestation infants, with 10% more than two standard deviations below the mean. All types of CP are more common in infants below average weight for gestation and this is most marked for the non-spastic types that are almost only seen in term, small-for-gestation infants. Gestational age is the crucial determinant of rate of CP and the increase in prevalence seen over the past 25 years is due to increased rates in preterm infants, not term infants. Both conclusions, suspected from birthweight analyses, are now demonstrated conclusively, with the contribution coming from those 32-36 weeks gestation as well as very preterm infants.

Gestational assessment assessed

AIMS

To review the accuracy with which obstetric information on gestation is recorded in the neonatal records; and the reliability of the methods used for assessing gestational age after birth.

METHODS

Service information on all babies born in 1989, and research information on all babies of < 32 weeks gestation born in the Northern Region in 1990-91, were reviewed to determine the accuracy with which antenatally collected information had been recorded in the neonatal records after birth. A prospective study was also mounted to assess how reliably paediatric staff could assess the gestational age of babies born to mothers with certain obstetric dates under service conditions. Paediatric residents looked at 347 babies of > 32 weeks gestation, and senior staff looked at 105 babies of < 30 weeks gestation.

RESULTS

The best techniques for estimating gestation immediately after birth were only half as accurate (95% CI +/- 17 days) as estimates based on antenatal ultrasound at 15-19 weeks gestation. Assessments that relied on the tone, posture, and appearance of the baby at birth in those of < 32 weeks gestation were less reliable than assessments based on a retrospective review of when various reflex responses first appeared. They also tended to overestimate true gestation. Antenatal information of high quality was ignored, and arithmetic and transcription errors were introduced during the transfer of antenatal information into over 10% of postnatal records.

CONCLUSIONS

Current ultrasound techniques for "dating" pregnancy antenatally are better than any of the methods of postnatal assessment. Given the reliability of the antenatal information now available, it is regrettable that so many inaccuracies have been allowed to creep into the routine computation and recording of gestation at birth.