The individualised birthweight ratio: a more logical outcome measure of pregnancy than birthweight alone

Br J Obstet Gynaecol. 1993 Apr;100(4):342-7. doi: 10.1111/j.1471-0528.1993.tb12977.x.


Objective: To provide a new outcome measure for pregnancy specifically related to the individual.

Design: Computer analysis of physiological factors affecting birthweight.

Setting: Two provincial teaching hospitals (University and City Hospitals, Nottingham) and an associated district general hospital (Derby City Hospital) serving a defined catchment area in the East Midlands.

Subjects: All women delivering in the above hospitals since the start of computerised obstetric records: 31,561 women with gestational age verified by early pregnancy ultrasound scan data.

Main outcome measures: Calculation of the predicted birthweight taking into account maternal and fetal physiological factors. Derivation of the individualised birthweight ratio (actual birthweight divided by predicted birthweight expressed as a percentage) for each individual baby.

Results: The individualised birthweight ratio redefines as normally grown 41% of babies below the 10th centile of crude birthweight for gestation. Other babies previously regarded as normal are redefined as growth retarded. At the upper end of the distribution 46% of those above the 90th centile of birthweight for gestation are redefined as normally grown.

Conclusions: The predicted birthweight can be calculated for an individual pregnancy at a given gestation. The standardised comparison between this predicted birthweight and the actual birthweight is a more logical reflection of the normality of intrauterine growth and therefore more logical as an outcome measure for pregnancy than crude birthweight for gestation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Birth Weight* / physiology
  • Body Height
  • Body Weight
  • Delivery, Obstetric
  • England / epidemiology
  • Female
  • Gestational Age
  • Humans
  • Male
  • Maternal Age
  • Pregnancy
  • Pregnancy Outcome*
  • Ultrasonography, Prenatal