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Intrauterine growth and its relationship to size and shape at birth
Peter C Hindmarsh1, Michael P P Geary, Charles H Rodeck
1London Centre for Paediatric Endocrinology and Metabolism, Institute of Child Health, University College, UK. p.hindmarsh@ucl.ac.uk
Insights
Fetal growth phenotypes, or body shape at birth, are primarily determined by proportionality, not specific gestational events. Ultrasound scans are poor predictors of birth size and shape, limiting their use in predicting growth problems.
Area of Science:
- Reproductive biology
- Fetal development
- Public health
Background:
- Epidemiological studies link birth size to adult cardiovascular disease risk.
- Fetal growth phenotypes, particularly disproportionate growth, are associated with specific cardiovascular disease components.
- The "Fetal Origins of Adult Disease" hypothesis requires validation in contemporary populations.
Purpose of the Study:
- To investigate the existence and characteristics of "growth phenotypes" within the normal distribution of birth size.
- To assess the predictive accuracy of antenatal ultrasound measurements for fetal growth and birth size.
- To examine the influence of maternal and fetal factors on birth size and shape.
Main Methods:
- Prospective study of 1650 low-risk, singleton, white pregnancies.
- Antenatal fetal growth assessed by ultrasound at 20 and 30 weeks gestation.
- Principal component analysis of birth measurements to define shape; correlation with antenatal ultrasound data.
Main Results:
- Significant sexual dimorphism observed in fetal anthropometric measures, with males generally larger.
- Maternal factors (parity, height, BMI) and smoking significantly influenced birth weight and dimensions.
- Principal component analysis identified proportionality as the primary determinant of birth shape (55% variance); antenatal ultrasound was a poor predictor of birth size.
Conclusions:
- Birth shape is largely determined by proportionality, not specific adverse events during gestation.
- Sexual dimorphism plays a significant role in fetal growth and body composition.
- Routine antenatal scans at 30 weeks are unlikely to be beneficial for predicting growth problems in low-risk pregnancies.
Abstract:
Birth size and shape are commonly used as indicators of fetal growth. Epidemiologic studies have suggested a relationship between birth size and the risk of developing cardiovascular disease in later life. Certain "growth phenotypes" have been linked to the development of certain components of cardiovascular disease, particularly babies who display disproportional growth in utero. These observations are based on retrospective analysis of historical data sets. If the "Fetal Origins of Adult Disease" hypothesis is to be generalisable to the present day, then it is essential to establish whether these "growth phenotypes" exist within the normal distribution of birth size. The UCL Fetal Growth Study is a prospective study of antenatal fetal growth assessed by ultrasound at 20 and 30 wk gestation in 1650 low risk, singleton, white pregnancies. Measures of birth size were obtained and analyzed by principal components to explain shape at birth. Birth measures were also related to antenatal growth measurements to determine the strength of ultrasound evaluation in determining subsequent growth. There was significant sexual dimorphism in all measures at birth, with males heavier, longer, and leaner than females. From 20 wk of gestation onwards, males had a significantly larger head size than females. Parity, maternal height, and body mass index were important determinants of birth weight (p < 0.001). Cigarette smoking influenced birth weight, length, and head circumference (p < 0.001) but had no effect on placental size. Principal component analysis revealed that proportionality was the predominant size/shape at birth (55% of variance explained). A further 18% of variance was explained by a contrast between weight, head circumference, and length versus three skinfolds. Anthropometric measures as assessed by ultrasound at 20 and 30 wk gestation were poor predictors of birth length, weight, and head circumference (adjusted R(2) 18, 40, and 28% at 30 wk gestation scan, respectively). These predictions were not improved by including growth patterns between 20 and 30 wk. There is sexual dimorphism in a number of anthropometric measures at birth and in utero. These sex differences are important determinants of body size and shape. In a low risk population delivering at term, body shape was largely determined by proportionality between anthropometric measures. The low correlations between antenatal measures and birth size suggest that it is unwise to ascribe birth shape phenotypes to adverse events at any particular stage of gestation. The weak relationship also suggests that routine antenatal scans around 30 wk of gestation to predict growth problems are unlikely to be of benefit in the majority of cases.