The most accurate models, with the lowest Euclidean distance and highest proportion of AE ≤ 10%, were provided by the formulae incorporating ≥ 3 rather than < 3 biometrical measurements. The systematic review identified 45 studies describing a total of 70 models for EFW by various combinations of measurements of fetal head circumference (HC), biparietal diameter, femur length (FL) and abdominal circumference (AC). The most accurate model with the lowest Euclidean distance and highest proportion of AE ≤ 10% was provided by the formula of Hadlock et al., published in 1985, which incorporated measurements of HC, AC and FL; there was a highly significant linear association between EFW and birth weight (r = 0.959; P < 0.0001), and EFW was within 10% of birth weight in 80% of cases. The performance of the best model developed in this study, utilizing HC, AC and FL, was very similar to that of Hadlock et al. CONCLUSION: Despite many efforts to develop new models for EFW, the one reported in 1985 by Hadlock et al., from measurements of HC, AC and FL, provides the most accurate prediction of birth weight and can be used for assessment of all babies, including those suspected to be either small or large. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Objective First‐trimester screening for pre‐eclampsia (PE) is useful because treatment of the high‐risk group with aspirin reduces the rate of early PE with delivery at < 34 weeks' gestation by about 80% and that of preterm PE with delivery at < 37 weeks by 60%. In previous studies, we reported that the best way of identifying the high‐risk group is by a combination of maternal factors, mean arterial pressure (MAP), uterine artery pulsatility index (UtA‐PI) and serum placental growth factor (PlGF). An alternative biochemical marker is pregnancy‐associated plasma protein‐A (PAPP‐A), which is used widely as part of early screening for trisomy. The objective of this study was to examine the additive value of PlGF and PAPP‐A in first‐trimester screening for preterm PE by maternal factors, MAP and UtA‐PI and define the risk cut‐off and screen‐positive rate to achieve a desired detection rate of PE if PAPP‐A rather than PlGF was to be used for first‐trimester screening. Methods This was a non‐intervention screening study. The data were derived from prospective screening for adverse obstetric outcomes in women with singleton pregnancy attending for a routine first‐trimester hospital visit. Patient‐specific risks of delivery with PE at < 37 weeks' gestation were calculated using the competing‐risks model to combine the prior distribution of gestational age at delivery with PE, obtained from maternal characteristics and medical history, with multiples of the median (MoM) values of MAP, UtA‐PI, PlGF and PAPP‐A. The performance of screening in the total population and in subgroups of women of white and black racial origin was estimated. McNemar's test was used to compare the detection rate, for a fixed screen‐positive rate, of screening with and without PlGF and PAPP‐A. Risk cut‐offs and screen‐positive rates to achieve desired detection rates of preterm PE were determined in screening with and without PlGF and PAPP‐A. Results The study population was composed of 60 875 singleton pregnancies, including 1736 (2.9%) that developed PE. There are three main findings of this study. First, the performance of first‐trimester screening for PE by a combination of maternal factors, MAP, UtA‐PI and PlGF is superior to that of screening by maternal factors, MAP, UtA‐PI and PAPP‐A; for example, in screening by maternal factors, MAP, UtA‐PI and PlGF, at a screen‐positive rate of 10%, the detection rate of PE with delivery at < 37 weeks' gestation was 74.1%, which was 7.1% (95% CI, 3.8–10.6%) higher than in screening by maternal factors, MAP, UtA‐PI and PAPP‐A. Second, addition of serum PAPP‐A does not improve the prediction of PE provided by maternal factors, MAP, UtA‐PI and PlGF. Third, the risk cut‐off and screen‐positive rate to achieve a given fixed detection rate of preterm PE vary according to the racial composition of the study population and whether the biomarkers used for screening are MAP, UtA‐PI and PlGF or MAP, UtA‐PI and PAPP‐A. For example, in screening by a combination of maternal factors, MAP, UtA‐PI and PlGF in ...

Objective Serum pregnancy‐associated plasma protein‐A (PAPP‐A) and placental growth factor (PlGF) at 11–13 weeks' gestation are reduced in pregnancies with fetal trisomy and in those that subsequently develop pre‐eclampsia (PE). In screening for trisomy, the established biochemical marker is PAPP‐A, whereas in screening for PE, the preferred marker is PlGF. The objective of this study was to examine the impact of replacing PAPP‐A by PlGF in first‐trimester screening for trisomies 21, 18 and 13 by maternal age, fetal nuchal translucency thickness (NT) and free β‐human chorionic gonadotropin (β‐hCG). Methods This was a prospective screening study in singleton pregnancies for trisomies 21, 18 and 13 by a combination of maternal age, fetal NT and serum PAPP‐A and free β‐hCG at 11–13 weeks' gestation in which we also measured PlGF. Multiples of the median (MoM) values were calculated for PAPP‐A, free β‐hCG and PlGF. The dataset was split randomly into training and test datasets of roughly equal size, and the parameters for PlGF obtained from the training dataset were used in risk calculation for the test dataset. Standardized detection rates were computed by obtaining the likelihood ratios for biochemistry and fetal NT for trisomy‐21, ‐18 and ‐13 pregnancies in the sample and then applying these to each year of maternal age from 12 to 50 to estimate the age‐specific detection rates. These were then weighted according to the maternal age distributions of trisomy‐21, ‐18 and ‐13 pregnancies in England and Wales in 2018. Similarly, standardized false‐positive rates (FPR) were computed by obtaining the likelihood ratios for biochemistry and NT, as appropriate, in normal pregnancies in the sample and then applying these to each year of maternal age from 12 to 50 to estimate the age‐specific FPRs. A modeling approach was used to assess the performance of screening according to gestational age at biochemical testing. Results The study population of 71 266 pregnancies included 70 858 (99.4%) with normal fetal karyotype or birth of a phenotypically normal neonate and 263 with trisomy 21, 109 with trisomy 18 and 36 with trisomy 13. There are five main findings of this study. First, the performance of screening for trisomy by the first‐trimester combined test or the combined test in which PAPP‐A is replaced by PlGF is substantially better at 11 than at 13 weeks' gestation; for example, the detection rates of trisomy 21 by the combined test were 94%, 90% and 84%, at 5% FPR, when testing was carried out at 11, 12 and 13 weeks, respectively, and the corresponding values in screening by a test in which PAPP‐A is replaced by PlGF were 90%, 87% and 86%, respectively. Second, in trisomy‐21 pregnancies, the deviation of median PAPP‐A MoM from normal decreases with increasing gestational age, whereas the deviation in PlGF does not change with gestational age. Third, the performance of screening for trisomy 21 during the 11th and 12th gestational weeks is superior if screening includes PAPP‐A rather than PlGF, whereas during the ...