Birthweight for length: ponderal index, body mass index or Benn index?

This study compares how effectively the ponderal index and the body mass index adjust birthweight for length at different gestations, and derives an improved index suitable for all gestations. The study was a cross-sectional survey, in a London teaching hospital, using a total of 999 neonates of 33 weeks gestation or later. Main outcome measures were the ponderal index (birthweight/length3), body mass index (birthweight/length2), and Benn index (birthweight/length(n)), where the length power n varies with gestation and is estimated by log-log regression. Results showed that up to 39 weeks gestation, the ponderal index is uncorrelated with length and so is a good index of birthweight for length. Past 39 weeks gestation, the ponderal index is negatively correlated with length, while the body mass index is uncorrelated, so that the body mass index is better. Neither index is optimal at all gestations. Deriving the Benn index (birthweight/length(n)) for each week of gestation, choosing n to make the index uncorrelated with length, shows that n falls steadily and very significantly (p < 0.0001) with increasing gestation. This in turn means that predicted birthweight for length depends on gestation: for a neonate 48 cm long, predicted birthweight varies from 2485 g at 34 weeks to 3030 g at 43 weeks, a 20% range. However, for a 54 cm long infant, predicted birthweight is the same at all gestations. A Benn index where the value of n changes linearly with gestation is described. We conclude that the ponderal index is not appropriate for measuring intra-uterine malnutrition, as it fails to adjust for length at all gestations. No other index of birthweight/length(n) with constant n is any better, as different gestations require different indices. Birthweight predicted from an infant's length depends on the infant's gestation. If, as Barker proposes, thinness at birth assessed by birthweight for length is used to predict later health status, more account needs to be taken of the complex relationship between birthweight, length and gestation.

Head circumference/abdominal circumference ratio, ponderal index and fetal malnutrition. Should head circumference/abdominal circumference ratio be abandoned?

Head circumference/abdominal circumference (HC/AC) ratios of the fetus are accepted as a means of distinguishing different patterns of growth retardation with a high ratio implying malnutrition of the fetus. Ponderal index (birthweight/length3) is used by paediatricians as a measure of neonatal wasting and would therefore be expected to correlate with HC/AC ratios at delivery. Anthropometric data on 999 newborn infants have been collected and analyzed by multiple regression. The results show a poor correlation between ponderal index and HC/AC ratio, worse than that between ponderal index and AC alone. The use of HC/AC ratios antenatally to identify subgroups of intrauterine malnutrition should be abandoned. The prediction of intrauterine malnutrition by weight/length ratios should be investigated further.

Can fetal gastroschisis always be diagnosed prenatally?

Fetal gastroschisis is regarded as a relatively straightforward ultrasound diagnosis. We report two cases of infants born with undiagnosed gastroschisis despite several detailed prenatal assessments following raised serum alphafetoprotein measurements. In both cases, the bowel was healthy with no evidence of long-term herniation through the abdominal wall and primary surgical correction was successful. Gastroschisis has previously been classified as 'antenatal' and 'perinatal', and we conclude that the latter type is not always possible to diagnose prenatally.

Abnormalities of the uterine cervix in women with vulval warts. A preliminary communication.

Fifty women attending a clinic for sexually transmitted diseases with vulval condylomata acuminata were examined by cervical cytology and colposcopy for cervical infection by human papillomavirus (HPV) or epithelial abnormality indicating cervical intraepithelial neoplasia (CIN) or both. Collated results showed a high prevalence of both conditions in these 50 women; 25 (50%) had evidence of cervical infection by HPV and 18 (36%) epithelial abnormalities consistent with CIN 1 or 2.