OP15.05: First trimester fetal growth: a screening tool for small‐for‐gestational‐age newborns

The study aimed to develop a predictive model for newborns small for gestational age (SGA) bellow the third percentile using clinical and biophysical markers, including Crown–rump length (CRL) and uterine artery Doppler (UAD) in the first trimester. It involved 3,238 women with a singleton pregnancy, assessing CRL before and after 11 weeks. A CRL growth rate was calculated for each pregnancy and expressed in mm/day. Additionally, UAD was performed between 11+0-13+6 weeks. Of these, 191 women delivered SGA newborns bellow the third percentile (5.8%), including 67 preterm SGA newborns (born before 37 weeks). UAD and CRL growth were compared between the SGA groups and gestational age-appropriate controls. Logistic regression analysis was used to evaluate whether any variable was significantly associated with the outcomes of newborns overall and preterm SGA. The CRL growth rate was between 1.34 and 1.86 mm/day in 90% of unaffected pregnancies. Clinical factors associated with SGA bellow the third percentile included reduced BMI, nulliparity, chronic hypertension, and lupus. Preterm SGA bellow the third percentile exhibited an increased UAD pulsatility index (2.02 ± 0.46 vs. 1.54 ± 0.46, p < 0.05) and reduced CRL growth (1.49 ± 0.20 vs. 1.57 ± 0.21, p < 0.05). With a fixed false positive rate of 10%, the logistic regression models showed 22.4% sensitivity for overall SGA bellow the third percentile and 43% for preterm SGA bellow the third percentile. This study concluded that reduced CRL growth in the first trimester in linked to SGA bellow the third percentile and that a combined model including maternal characteristics, CRL growth, and UAD can predict around half of pregnancies with preterm SGA.