Prediction of birth weight by fetal crown-rump length and maternal serum levels of pregnancy-associated plasma protein-A in the first trimester.
OBJECTIVE
To determine whether the first trimester crown-rump length (CRL), maternal serum levels of pregnancy-associated plasma protein A (PAPP-A) and free beta-human chorionic gonadotropin (fbeta-hCG) are independent predictors of birth weight.


METHODS
This was an observational study over 1.5 years in Chinese patients who underwent first-trimester combined screening for Down syndrome in a University fetal medicine unit. After excluding cases with multiple pregnancies, congenital malformations and in-utero deaths, the relationship between fetal CRL (expressed as standardized Z-score (Z-CRL)), maternal PAPP-A and fbeta-hCG levels (expressed as log(10) of multiples of the median) and birth weight (Z-BW) were analyzed by Pearson's correlation test followed by multiple regression to check for their independency. The predictive power of the independent predictors for small-for-gestational age (SGA, defined as birth weight < 10(th) centile) was then assessed using receiver-operating characteristics (ROC) curves, and the likelihood ratios were derived.


RESULTS
A total of 2760 cases were included. Z-CRL, log(10) PAPP-A(MoM), and log(10) fbeta-hCG were positively correlated with Z-BW (P < 0.0001), but only Z-CRL and log(10) PAPP-A(MoM) were independent predictors (P < 0.0001). The areas under the ROC curves of PAPP-A(MoM) and Z-CRL were 0.608 and 0.593, respectively (P < 0.0001). Likelihood ratios increased with decreasing PAPP-A(MoM) and Z-CRL, but were around 1 when the markers were at or above the mean.


CONCLUSIONS
First-trimester CRL and PAPP-A are independent factors that influence final birth weight. The lower the PAPP-A and the smaller the CRL, the higher the risk of a fetus becoming SGA. However, their predictive powers are not sufficiently good for them to be used alone for SGA screening.
D000328:Adult; D015415:Biomarkers / Q000378:metabolism; D001724:Birth Weight / Q000502:physiology; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000378:metabolism*; D018568:Crown-Rump Length; D005260:Female; D005317:Fetal Growth Retardation / Q000175:diagnosis*; D006801:Humans; D011237:Predictive Value of Tests; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000097:blood; D011266:Pregnancy-Associated Plasma Protein-A / Q000378:metabolism*; D011296:Prenatal Diagnosis / Q000379:methods*; D012680:Sensitivity and Specificity
D015415:Biomarkers; D018997:Chorionic Gonadotropin, beta Subunit, Human; D011266:Pregnancy-Associated Plasma Protein-A