The monitoring of fetal weight is an important aspect of antenatal care. To construct an individually adjustable standard, we developed a model to link the predicted birth weight to a fetal weight curve which outlines how this weight is to be reached in an uncomplicated pregnancy. A formula was derived which describes the median fetal weight at each gestation as a proportion of the optimal term weight, and also defines the 90th and 10th centile curves as normal limits. We analyzed a birth weight database of 38,114 singleton, routine ultrasound-dated pregnancies resulting in term deliveries. By stepwise multiple regression analysis, we derived coefficients for the factors that act as variables on term birth weight in our population. Apart from gestational age and sex, the maternal height, weight at first visit, ethnic group, parity and smoking all have significant and independent effects on birth weight. The variation due to ethnic group appears to be physiological in this population. Smoking is associated with a reduction in birth weight, which is independent of maternal physique and related to the number of cigarettes per day as reported at the first visit. We have developed a software program which calculates, on the basis of pregnancy variables entered at the first visit, an adjusted normal range for fetal size. This can be printed out as a chart and used for antenatal surveillance of growth.

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Objective To study the characteristics of birthweight and gestational age of third trimester fetal deaths which occurred before the onset of labour, Design Review of computerised confidential perinatal mortality records. Data originated from the 1992 Trent Region Perinatal Mortality Survey.Sample One hundred and forty-nine antepartum stillbirths of at least 24 weeks of gestation confirmed by early ultrasound scan. Congenital abnormalities and multiple pregnancies were excluded.Main outcome measures Reported causes of stillbirth, weight-for-gestational age centiles based on a standard derived from normal pregnancies; pregnancy characteristics compared with the local maternity population.Results Of 149 stillbirths, 83 (56%) were preterm and 66 were at term, and the majority (126; 85%) occurred from 3 1 weeks. Most of the deaths (97; 65%) were reported as 'unexplained' even though post-mortems had been carried out in 60% of all cases. Using a gestational age-specific fetal weight standard derived from normal, term live births, 41% of all cases of stillborn infants were small-forgestational age (< 10th centile; OR 6.2; 95% CI 3.3-1 1.5); 39% of which had been classified as unexplained were small for gestational age (OR 5.6; 2.6-12.0). This excess of small stillbirths was most pronounced between 3 1 and 33 weeks, where the weights of 63% of all stillbirths and 72% of unexplained fetal deaths were < 10th centile. Overall, a higher proportion of preterm (< 37 weeks) than term stillbirths were small for gestational age: 53% vs 26% (OR 3.3; 1.6-6.5). However, at term there were also more subtle differences in weight deficit, with more fetuses with a weight between the 10th and 50th centiles than between 50th and 90th (36 vs 11; OR 3.3; 1-4-7.8). Mothers of pregnancies ending in stillbirth were similar in age, size, parity and ethnic group to mothers of live born babies, but were more likely to be smokers (37 vs 27%, OR 1.6; 1.2-2.3).Conclusions Many stillborn babies are small for gestational age. In the absence of significant differences in physiological pregnancy characteristics, this is unlikely to be a constitutional smallness, but represents a preponderance of intrauterine growth restriction. For a full appreciation of the strength of this association, appropriate weight standards and classifications need to be applied in perinatal mortality surveys. Many antepartum stillbirths which are currently designated as unexplained may be avoidable if slow fetal growth could be recognised as a warning sign.

Objective-To produce standard curves of birth weight according to gestational age validated by ultrasonography in the British population, with particular reference to the effects ofethnic origin.Design-Retrospective analysis of computerised obstetric database.Setting-Three large maternity units associated with Nottingham University with over 16000 deliveries a year.Patients-41 718 women with ultrasound dated singleton pregnancies and delivery between 168 and 300 days' gestation.Main outcome measures-Length of gestation, ethnic origin, parity, maternal height and weight at booking, smoking during pregnancy; the effect of these variables on birth weight.Results-Birth weights from ultrasound dated pregnancies have a higher population mean and show less flattening of the birthweight curve at term than those of pregnancies dated from menstrual history. Significant differences were observed in mean birth weights ofbabies ofmothers ofEuropean origin (3357 g), ofAfro-Carribean origin (3173 g), and from the Indian subcontinent (3096 g). There were also significant interethnic differences in length of gestation, parity, maternal height, booking weight, and smoking habit which affected birth weight. The ethnic differences in birth weight were even greater when the effect ofsmoking was excluded.Conclusions-Birthweight standards require precise dating of pregnancy and should describe the population from which they were derived. In a heterogeneous maternity population the accurate assessment of an individual baby's weight needs to take the factors which affect birthweight standards into consideration. IntroductionThe standard curves of birth weight that are commonly used in Britain are adjusted for gestational age as well as sex and parity.1-3 Gestational age needs to be known accurately to calculate individual birthweight centiles correctly. These population standards were derived before routine ultrasound scanning allowed accurate dating of each pregnancy, and they had to rely on dates based on the last menstrual period. Use of menstrual history is unreliable,45 even when it is

Asian women largely prefer a vaginal delivery, and their attitude toward cesarean delivery on demand is comparable with that of Western women. Cultural or ethnic differences are unlikely to affect maternal preference for cesarean delivery in Singapore women.