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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 31 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-for-gestational age (< 10th centile; OR 6.2; 95% CI 3.3-11.5); 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 31 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.

The objective of this study was to investigate the size of singleton vs twin pregnancies at the time of a second trimester dating scan. The analysis included 86 infants from 63 pregnancies achieved with assisted reproductive techniques, comprising 40 singletons and 46 twins. Measurements of second trimester biparietal diameter (n = 85) and femur length (n = 74) were plotted against the precisely known gestational age. A common regression line was calculated for each parameter and the residuals for singletons and twins were compared. Gestational age and weight at birth were also analysed for each group. There was no significant difference between singletons and twins in biparietal diameter or femur length in second trimester. In contrast, twins had a lower mean birthweight, gestational age at birth, and weight-for-gestational age centile compared with singletons. Singleton babies from these pregnancies had an average birthweight centile of 49.8% (i.e. close to the median for spontaneously conceived pregnancies in our population). We concluded that the same pregnancy dating charts can be used for singletons and twins. At corresponding gestational age, twins are smaller than singletons at birth because of slower growth in the third trimester.