Objective
To assess the external validity of all published firstâtrimester prediction models based on routinely collected maternal predictors for the risk of smallâ and largeâforâgestationalâage (
SGA
and
LGA
) infants. Furthermore, the clinical potential of the bestâperforming models was evaluated.
Design
Multicentre prospective cohort.
Setting
Thirtyâsix midwifery practices and six hospitals (in the Netherlands).
Population
Pregnant women were recruited at <16Â weeks of gestation between 1 July 2013 and 31 December 2015.
Methods
Prediction models were systematically selected from the literature. Information on predictors was obtained by a webâbased questionnaire. Birthweight centiles were corrected for gestational age, parity, fetal sex, and ethnicity.
Main outcome measures
Predictive performance was assessed by means of discrimination (Câstatistic) and calibration.
Results
The validation cohort consisted of 2582 pregnant women. The outcomes of
SGA
<10th percentile and
LGA
>90th percentile occurred in 203 and 224 women, respectively. The Câstatistics of the included models ranged from 0.52 to 0.64 for
SGA
(
n
=Â 6), and from 0.60 to 0.69 for
LGA
(
n
=Â 6). All models yielded higher Câstatistics for more severe cases of
SGA
(<5th percentile) and
LGA
(>95th percentile). Initial calibration showed poorâtoâmoderate agreement between the predicted probabilities and the observed outcomes, but this improved substantially after recalibration.
Conclusion
The clinical relevance of the models is limited because of their moderate predictive performance, and because the definitions of
SGA
and
LGA
do not exclude constitutionally small or large infants. As most clinically relevant fetal growth deviations are related to âvascularâ or âmetabolicâ factors, models predicting hypertensive disorders and gestational diabetes are likely to be more specific.
Tweetable abstract
The clinical relevance of prediction models for the risk of smallâ and largeâforâgestationalâage is limited.