The impact of exotic species on native organisms is widely acknowledged, but poorly understood. Very few studies have empirically investigated how invading plants may alter delicate ecological interactions among resident species in the invaded range. We present novel evidence that antifungal phytochemistry of the invasive plant, Alliaria petiolata, a European invader of North American forests, suppresses native plant growth by disrupting mutualistic associations between native canopy tree seedlings and belowground arbuscular mycorrhizal fungi. Our results elucidate an indirect mechanism by which invasive plants can impact native flora, and may help explain how this plant successfully invades relatively undisturbed forest habitat.

Objective To construct new size charts for fetal head circumference, biparietal diameter and other head dimensions. Design A prospective, cross sectional study. Setting The routine ultrasound department of a London teaching hospital. Subjects The fetuses of 663 women seen in the routine antenatal booking clinic whose ultrasound and menstrual dates agreed within 10 days. Methods Fetuses were scanned once only for the purpose of the study at gestations between 12 and 42 weeks, when up to 20 dimensions were measured. For each measurement separate regression models were fitted to estimate the mean and standard deviation at each gestational age. Centiles were derived by combining these two regression models, assuming that the measurements have a normal distribution at each gestational age. Results A total of 594 fetuses had their biparietal diameter measured and their head circumference measured directly. Both head diameters were recorded for 587 fetuses and the circumference was also derived from these, as was the cephalic area. New charts are presented for biparietal diameter (both outer–outer and outer–inner), head circumference (directly measured and derived from diameters). The directly measured head circumferences were consistently (by about 1%) greater than those derived from measurement of the head diameters. The new charts are compared with previously published charts that are in wide use. Charts for occipitofrontal diameter, cephalic index and cephalic area are also presented. Conclusions We have constructed new size charts for the fetal biparietal diameter and for head circumference, both measured directly and derived from head diameters. We have demonstrated the difference between the size charts constructed from these two sets of values and hence the importance of using the appropriately derived chart when assessing the head circumference. The differences between the new charts for biparietal diameter and head circumference and previous ones may be largely due to methodological differences.

Summary A method of estimating fetal weight by ultrasonic measurement of the fetal abdominal circumference is described. Assessment of birth weight predictions on 140 fetuses who were delivered within 48 hours of this measurement showed that the accuracy of predictions varied with the size of the fetus; at a predicted weight of 1 kg, 95 per cent of birth weights fell within 160 g, while at 2 kg, 3 kg and 4 kg the corresponding values were 290 g, 450 g and 590 g respectively. Expressed as a percentage of the predicted weight, confidence limits remained constant throughout the birth weight range. Extrapolation of these data to routine screening of the obstetric population showed that with a single measurement at 32 weeks menstrual age, 87 per cent of babies below the 5th centile would be detected by this method but that the diagnosis rate would fall to 63 per cent at 38 weeks. The false positive diagnosis rate would remain constant between 32 and 38 weeks at just over 1 per cent.

Fetal compromise is associated with significant alterations in the fetal arterial and venous circulation. Significant changes in venous Doppler waveforms develop due to increased afterload and perhaps myocardial failure in late deterioration after fetal arterial redistribution is established and seem to be closely related to abnormal biophysical assessment findings. Therefore, Doppler investigation of the fetal venous circulation may play an important role in monitoring the redistributing growth retarded fetus and thereby may help to determine the optimal time for delivery.

This cross-sectional study establishes reference ranges with gestation for Doppler parameters of fetal venous and atrioventricular blood flow. Color flow Doppler was used to examine 143 normal singleton pregnancies at 20-40 weeks' gestation. Flow velocity waveforms were recorded from the ductus venosus, right hepatic vein and inferior vena cava. The waveforms are triphasic, reflecting ventricular systole, early diastole and atrial contraction. Peak velocities for these parameters were measured with pulsed Doppler and a new index, the peak velocity index for veins (PVIV), was calculated. Similarly, time-averaged maximum velocities for the whole cardiac cycle were measured and the pulsatility index for veins (PIV) was calculated. Flow velocity waveforms were also recorded at the level of the atrioventricular valves and the ratios of peak velocities at early diastolic filling (E) and atrial contraction (A) were calculated. Regression analysis was used to define the association of each measured and calculated Doppler parameter with gestational age. Blood flow velocities in the fetal veins and velocities and E/A ratios across the atrioventricular valves increased significantly with gestation, whereas PVIV and PIV decreased. Blood flow velocities were highest in the ductus venosus and lowest in the right hepatic vein, and PVIV and PIV were highest in the hepatic vein and lowest in the ductus venosus. In the ductus venosus, there was always forward flow throughout the heart cycle, whereas in the inferior vena cava and hepatic vein during atrial contraction, flow was away from or towards the heart or there was no flow. Pulsatility of flow velocity waveforms in the venous system is the consequence of changes in pressure difference between the venous system and the heart during the heart cycle. The finding that PVIV and PIV decrease with gestation is consistent with decreasing cardiac afterload and maturation of diastolic ventricular function.

The use of Doppler studies of the uterine arteries in the prediction of pre-eclampsia and intrauterine growth retardation has had mixed success. The introduction of color Doppler imaging and the use of the "notch' to define an abnormal waveform have helped to improve the predictive value of uterine artery Doppler screening. The aim of this study was to evaluate the use of uterine artery Doppler in a group of women of mixed race and parity. This study was a prospective, cross-sectional analysis of 1326 unselected women who were screened with continuous wave uterine Doppler at 19-21 weeks, as part of a fetal anomaly/dating scan. A total of 214 women with abnormal uterine artery waveforms (notching) were referred for assessment at 24 weeks; 191 attended and had color Doppler imaging/pulsed Doppler studies of both uterine arteries. Data from 185 pregnancies were suitable for analysis. There were abnormal uterine Doppler findings (uni- or bilateral notching) in 110 patients at 24 weeks; 48 had bilateral notching. The sensitivity of notching for the prediction of proteinuric pregnancy-induced hypertension (PPIH) was similar in primiparas (76.9%), multiparas (77.7%), African-Caribbean women (82.6%) and Caucasian women (71.4%). The sensitivity of bilateral notching for the prediction of PPIH requiring delivery before 34 weeks was 81.2%, and 57.6% for babies small for gestational age (SGA), with positive predictive values of 27% (PPIH), 31.2% (SGA) and 37.5% (any complication). Patients with persistent bilateral notching are particularly at risk of developing PPIH or delivering an SGA baby before 34 weeks' gestation; they warrant increased surveillance, and may be a group that could benefit from prophylactic therapies.

Summary Fetal head and abdomen circumference measurements have been made using pulsed ultrasound techniques. The mean head to abdomen (H/A) circumference ratio with 95 per cent confidence limits was determined in 568 normal pregnancies from 17 to 41 weeks menstrual age. The mean ratio was 1·18 at 17 weeks, but decreased slowly until 29 weeks when the ratio was 1·11; thereafter there was a sharp fall in the mean ratio to 1·01 at 36 weeks and 0·96 at 40 weeks. The H/A circumference ratio was also determined in 31 small‐for‐dates fetuses within one week of delivery. In all cases the fetal weight as predicted from the fetal abdomen circumference measurement was below the 5th centile weight for gestation. The ratio was above the 95th centile limit in 22 (71 per cent) of these fetuses and evidence is presented to suggest that the H/A circumference ratio can be used to distinguish between symmetrical and asymmetrical growth retardation.

In order to achieve a clinical pregnancy rate higher than that achieved following initial adoption of in-vitro fertilization embryo transfers, more than one embryo is transferred. This has led to a substantial increase in unwanted multiple pregnancy rates with IVF as compared with natural conception. What is therefore required is a simple, clinically useful embryo scoring system, to reflect embryo developmental potential, which will enable the selection of the optimal number of embryos to transfer in order to achieve the maximum pregnancy rate with a low incidence of high order multiple pregnancies. We believe that the Cumulative Embryo Score (CES) achieves these aims. On the day of embryo transfer the grade of each embryo transferred was multiplied by the number of blastomeres to produce a score for each embryo, and summation of the scores obtained for all the embryos transferred gave the CES. The grouped pregnancy rates obtained rose as the CES increased to maximum of 42. A continued increase in the CES above 42 did not result in any further rise in the pregnancy rate. However, an analysis of all our IVF pregnancies showed that the multiple pregnancy rate continued to rise above a CES of 42. By restricting the CES per embryo transfer to 42, 78% of triplet pregnancies and 100% of the quadruplet IVF pregnancies could have been predicted and potentially avoided.