Objective. To study the association between maternal weight gain in pregnancy and fetal abdominal circumference in the second trimester. Design. Prospective cross-sectional study. Setting. Low-risk antenatal clinic. Population. Six hundred and fifty women with low-risk pregnancy. Methods. Women with a regular menstrual period (28±4 days) and certain information on the last menstrual period were recruited when they were referred for routine ultrasound scanning. Women with a discrepancy of>14 days between ultrasound and menstrual age were excluded. Maternal weight gain during pregnancy was derived from information in the antenatal chart and the weekly weight gain was calculated. Fetal abdominal circumference measurements were registered in gestational weeks 15–25 and their z-scores, together with the z-scores of maternal weight gain, were used in a linear regression analysis. Main outcome measures. Association between maternal weight gain and fetal abdominal circumference. Results. Based on the complete data of 515 women we found a mean maternal weight gain during pregnancy of 0.39kg/week and a positive association between this weight gain and fetal abdominal circumference in the second trimester (r=0.122 (95%CI 0.051–0.194)), with the strongest effect in women with the slowest weight gain (<0.28kg/week) (r=0.554 (95%CI 0.261–0.846)). Conclusion. Maternal weight gain in pregnancy is related to and may determine fetal abdominal circumference in gestational weeks 15–25, particularly in those women with a slow weight gain.
Linked article : This is a mini commentary on Ego et al., pp. 729–739 in this issue. To view this article visit https://doi.org/10.1111/1471‐0528.17399 .
Umbilical venous pulsation is an important sign of hemodynamic compromise, but is also found under normal physiological conditions. Mathematical modeling suggests that vascular compliance is a determinant for pulsation, and we tested this by studying velocity pulsation at three sites on the umbilical vein.In a cross-sectional study of 279 low-risk pregnancies (20-40 weeks' gestational age) blood flow velocity in the umbilical vein was determined before, within and after the umbilical ring in the fetal abdominal wall, and the incidence and magnitude of pulsation (the difference between the maximum and minimum velocity during a pulse, and pulsatility index) were noted. Based on the fact that the vessel cross-sectional area is an important determinant of compliance, we measured the diameter and time-averaged maximum velocity to reflect variation in diameter and compliance at the three sites.The incidence of umbilical venous pulsation was higher at the umbilical ring in the abdominal wall (242/279, 87%, 95% CI 82-90) than in the cord (43/198, 22%, 95%CI 16-27) or intra-abdominally (84/277, 30%, 95% CI 25-36) (P < 0.001). When pulsation was observed intra-abdominally, the pulsatility was not different from that at the umbilical ring (P = 0.16). However, the lowest pulsatility was found in the cord vein (P < 0.0001), where the largest vein diameter was found.The high incidence of venous pulsation at the umbilical ring where diameter and compliance are low supports the suggestion that local compliance is an important factor influencing pulsation in fetal veins.
Based on the hypothesis that fetal breathing movements (FBM) enhance sections of the circulation to meet the needs of gas transport, we studied the effects of FBM on the fetal inferior vena cava (IVC), which transports blood with the lowest oxygen saturation in the fetal body.One-hundred and ten women with low-risk singleton pregnancies were included in a longitudinal study during the second half of pregnancy. Inner diameter, peak systolic velocity and time-averaged maximum blood velocity were measured in the IVC below the ductus venosus outlet during rest and FBM. Volume flow and pressure gradient were estimated in 55 observations of forced inspiratory movements at 36 weeks of gestation. The results are presented as mean and 95% CI of the mean.Based on 585 observations obtained during fetal rest and FBM, we found no difference in diameter, 0.42 (95% CI, 0.41-0.43) cm vs. 0.41 (95% CI, 0.39-0.42) cm, respectively, apart from during high-amplitude inspiratory movement, when the diameter was 0.15 (95% CI, 0.13-0.17) cm. The peak systolic velocity was different during rest and FBM, 34.0 (95% CI, 32.7-35.3) cm/s vs. 81.5 (95% CI, 76.2-87.5) cm/s, respectively, and correspondingly for time-averaged maximum velocity, 19.7 (95% CI, 18.9-20.5) cm/s vs. 37.2 (95% CI, 34.9-39.9) cm/s, respectively. Forced inspiratory movements at 36 weeks significantly reduced flow in the IVC compared with rest, 63.6 (95% CI, 44.4-88.1) mL/min vs. 186.0 (95% CI, 142.8-238.1) mL/min, respectively. The pressure gradient increased 14-fold during forced inspiration, from 0.64 to 8.76 mmHg.High-amplitude fetal inspiration substantially constricts the abdominal IVC and creates a negative pressure in the chest. The IVC constriction withholds abdominal blood, thus temporarily giving way to other flows.
The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) is a scientific organization that encourages sound clinical practice, teaching and research related to diagnostic imaging in women's healthcare. The ISUOG Clinical Standards Committee (CSC) has a remit to develop Practice Guidelines and Consensus Statements as educational recommendations that provide healthcare practitioners with a consensus-based approach for diagnostic imaging. They are intended to reflect what is considered by ISUOG to be the best practice at the time at which they are issued. Although ISUOG has made every effort to ensure that Guidelines are accurate when issued, neither the Society nor any of its employees or members accepts any liability for the consequences of any inaccurate or misleading data, opinions or statements issued by the CSC. They are not intended to establish a legal standard of care because interpretation of the evidence that underpins the Guidelines may be influenced by individual circumstances and available resources. Approved Guidelines can be distributed freely with the permission of ISUOG (info@isuog.org). This document is a Practice Guideline on how to perform Doppler ultrasonography of the fetoplacental circulation. It is of the utmost importance not to expose the embryo or fetus to unduly harmful ultrasound energy, particularly in the earliest stages of pregnancy. At these stages, Doppler recording, when clinically indicated, should be performed at the lowest possible energy levels. ISUOG has published guidance on the use of Doppler ultrasound at the 11 to 13 + 6-week fetal ultrasound examination1. When performing Doppler imaging, the displayed thermal index should be ≤ 1.0 and the exposure time should be kept as short as possible, usually no longer than 5–10 min. It is not the intention of this Guideline to define clinical indications, specify appropriate timing of Doppler examination in pregnancy or discuss how to interpret findings or the use of Doppler in fetal echocardiography. The aim is to describe pulsed Doppler ultrasound and its different modalities: spectral Doppler, color flow mapping and power Doppler, which are commonly used to study the maternal–fetal circulation. We do not describe the continuous-wave Doppler technique, because this is not usually applied in obstetric imaging; however, in cases in which the fetus has a condition leading to very high-velocity blood flow (e.g. aortic stenosis or tricuspid regurgitation), it might be helpful in order to define clearly the maximum velocities by avoiding aliasing. The techniques and practices described in this Guideline have been selected to minimize measurement error and improve reproducibility. They may not be applicable in certain clinical conditions or for research protocols. Details of the grades of recommendation used in this Guideline are provided in Appendix 1. Reporting of levels of evidence is not applicable to this Guideline. All Doppler modalities are based on three fundamental principles. (1) Moving structures change the frequency and amplitude of reflected ultrasound signals. Moving structures include not only blood, but also fetal vessels or tissues. This can generate a shift in the backscattered signals. (2) Analysis of the components of the reflected signals are utilized for different Doppler modalities: the shift in frequency for directional color and spectral Doppler, and the shift in amplitude for power Doppler ultrasound (PDU). (3) All color and power Doppler modalities are pulsed techniques, while spectral Doppler can be pulsed or continuous. PRF, or scale, is the frequency at which the ultrasound signals (pulses) are emitted; a low PRF allows signals from slow-moving targets to reach the transducer before the next pulse is emitted, whereas a high PRF will allow only high velocities to reach the ultrasound transducer before the next pulse. The wall filter is a barrier defined by a specific threshold frequency below which signals are not displayed in the Doppler image. Gain is the amplification of signals. The quality and reproducibility of the recordings can be improved by knowledge of these Doppler settings and how to adjust them. Using real-time color Doppler ultrasound, the main branch of the uterine artery is located easily at the cervicocorporeal junction. Doppler velocimetry measurements are usually performed near to this location, either transabdominally2 or transvaginally3-5. While absolute velocities are of little or no clinical importance, semiquantitative assessment of the velocity waveforms is commonly employed. Measurements should be reported independently for the right and left uterine arteries, and the presence of notching should be noted. (GOOD PRACTICE POINT) Notching is defined qualitatively as reduced early diastolic velocities before the maximum diastolic velocity in the Doppler waveform. The severity of notching is defined by the difference between the lower early and the maximum diastolic velocities6. Note that, in women with congenital uterine anomaly, assessment of uterine artery Doppler indices and their interpretation is unreliable, since all published studies have been on women with (presumed) normal anatomy. (GOOD PRACTICE POINT) There is a significant difference in Doppler indices measured at the fetal end (intra-abdominal)11, in a free loop and at the placental end of the umbilical cord12. The impedance is highest at the fetal end, and absent/reversed EDV is likely to be seen first at this site. Reference ranges for umbilical artery Doppler indices at each of these sites have been published11, 13. For the sake of simplicity and consistency, by convention, measurements should be made in a free cord loop. (GOOD PRACTICE POINT) The decision to use a free loop of the cord was made early in the history of Doppler ultrasound and has been applied with great clinical success. However, in multiple pregnancies, and/or when comparing repeated measurements longitudinally, recordings from fixed sites, i.e. fetal end, placental end or intra-abdominal portion, may be more reliable. Appropriate reference ranges should be used according to the site of interrogation. Figure 3 shows examples of acceptable and unacceptable velocity waveform recordings and Figure 4 illustrates the influence of the vessel wall filter. Note that, in multiple pregnancy, assessment of umbilical artery blood flow can be challenging, since there may be difficulty in assigning a cord loop to a particular fetus. It is therefore better to sample the umbilical artery just distal to the abdominal insertion of the umbilical cord. However, the impedance there is higher than that in a free loop and that at the placental cord insertion, so appropriate reference charts are needed. (GOOD PRACTICE POINT) Note also that, in a two-vessel cord, at any gestational age, the diameter of the single umbilical artery is larger than the arterial diameter would be if there were two arteries14. Due to the different hemodynamics, the recorded velocity waveform in such cases should be interpreted with caution when using conventional reference ranges. (GOOD PRACTICE POINT) S/D ratio, RI and PI are the three best known indices to describe arterial flow velocity waveforms. All three are highly correlated. RI and S/D ratio estimate the relationship between PSV and EDV in the Doppler waveform (RI = (S − D)/S, S/D ratio = S/D, where S is peak systolic velocity and D is end-diastolic velocity). PI takes into account the PSV, the EDV and the time-averaged mean of the maximum frequency shift over the cardiac cycle (PI = (S − D)/TAMX, where S is peak systolic velocity, D is end-diastolic velocity and TAMX is the maximum velocity recorded in the MVE averaged over the cardiac cycle; TAMX should not be confused with time-averaged intensity-weighted mean velocity (TAV or Vm)). In Doppler waveforms showing dynamic changes in the systolic or diastolic components (i.e. in case of uterine artery waveform with presence of notching, or reversed EDV in umbilical artery waveform), PI gives a better estimate of the characteristics of the waveform than do RI or S/D ratio. PI shows a linear correlation with vascular resistance, as opposed to both S/D ratio and RI, which show a parabolic relationship with increasing vascular resistance31. Additionally, PI does not approach infinity when there are absent or reversed diastolic values. PI is the index recommended for use in clinical practice and research. (GOOD PRACTICE POINT) There is currently no high-level evidence to indicate how either CPR or UCR should be utilized in clinical management. Two indices are described for pulsed-wave Doppler analysis of the veins. The most commonly used is the pulsatility index for veins (PIV)32. This is calculated as PIV = (Vs − Va)/TAMX, where Vs is the peak forward velocity during ventricular systole and Va is the lowest forward velocity or peak reversed velocity during atrial contraction (the ‘a-wave’). The peak velocity index for veins (PVIV) is reported less frequently and is not featured on most auto-measure packages. PVIV is calculated as (Vs − Va)/Vd, where Vd is the peak forward velocity during atrial contraction (diastole). The use of PIV is recommended in clinical practice. (GOOD PRACTICE POINT) This Guideline presents the most commonly used techniques in clinical obstetrics, backed by solid scientific documentation. We are aware of important uses and sections of the circulation not mentioned herein, although these vessels and measurements may be of crucial importance in certain individuals. These vessels include, for example, the umbilical vein, hepatic artery, left portal vein and superior vena cava. However, the principles presented in this Guideline are valid for all fetal Doppler examinations. A. Bhide, Fetal Medicine Unit, St George's University Hospital and St George's University of London, London, UK G. Acharya, Division of Obstetrics and Gynecology, Department of Clinical Science, Intervention and Technology, Karolinska Institutet & Center for Fetal Medicine, Karolinska University Hospital, Stockholm, Sweden and Women's Health and Perinatology Research Group, Faculty of Medicine, University of Tromsø and University Hospital of Northern Norway, Tromsø, Norway A. Baschat, Johns Hopkins Center for Fetal Therapy, Department of Gynecology & Obstetrics, Johns Hopkins University, Baltimore, MD, USA C. M. Bilardo, Department of Obstetrics and Gynecology Amsterdam UMC, Amsterdam and Academic Medical Center Groningen, University of Groningen, Groningen, The Netherlands C. Brezinka, Univ Klinik fuer Gynaekologie und Geburtshilfe, Innsbruck, Austria D. Cafici, Sociedad Argentina de Ultrasonografía en Medicina y Biología, Argentina C. Ebbing, Department of Obstetrics and Gynecology, Haukeland University Hospital, and Department of Clinical Medicine, University of Bergen, Bergen, Norway E. Hernandez-Andrade, Department of Obstetrics and Gynecology and Reproductive Sciences, McGovern Medical School, University of Texas, Health Science Center at Houston (UTHealth), Houston, TX, USA K. Kalache, Gynaecology, Charité, CBF, Berlin, Germany J. Kingdom, Maternal-Fetal Medicine Division, Department of Obstetrics & Gynaecology, Mount Sinai Hospital, University of Toronto, Toronto, Canada T. Kiserud, Department of Clinical Science, University of Bergen and Department of Obstetrics and Gynecology, Haukeland University Hospital, Bergen, Norway S. Kumar, Mater Research Institute, University of Queensland, Brisbane, Australia W. Lee, Texas Children's Fetal Center, Texas Children's Hospital Pavilion for Women, Department of Obstetrics and Gynecology, Baylor College of Medicine, Houston, TX, USA C. Lees, Centre for Fetal Care, Queen Charlotte's & Chelsea Hospital, Imperial College Healthcare NHS Trust, London, UK and Department of Development & Regeneration KU Leuven, Leuven, Belgium K. Y. Leung, Department of Obstetrics and Gynaecology, Queen Elizabeth Hospital, Hong Kong G. Malinger, Division of Ob-Gyn Ultrasound, Lis Maternity Hospital, Tel Aviv Sourasky Medical Center and Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel G. Mari, Women's Health Institute, Department of Obstetrics and Gynecology, Cleveland Clinic Foundation, Cleveland, OH, USA F. Prefumo, Division of Obstetrics and Gynaecology, Department of Clinical and Experimental Sciences, University of Brescia, Brescia, Italy W. Sepulveda, FETALMED – Maternal-Fetal Diagnostic Center, Fetal Imaging Unit, Santiago, Chile B. Trudinger, Department of Obstetrics and Gynaecology, University of Sydney, Sydney, Australia This Guideline should be cited as: ‘Bhide A, Acharya G, Baschat A, Bilardo CM, Brezinka C, Cafici D, Ebbing C, Hernandez-Andrade E, Kalache K, Kingdom J, Kiserud T, Kumar S, Lee W, Lees C, Leung KY, Malinger G, Mari G, Prefumo F, Sepulveda W, Trudinger B. ISUOG Practice Guidelines (updated): use of Doppler velocimetry in obstetrics. Ultrasound Obstet Gynecol 2021; 58: 331–339.’
Monitoring fetuses at risk for developing anemia or placental compromise involves serial assessments of blood flow in the middle cerebral artery (MCA). However, the reference ranges for the indices currently in use are based on cross-sectional studies. The purpose of the present study was to establish new reference ranges suitable for serial measurements of MCA Doppler velocities and indices, and to provide terms for conditional reference intervals for individual serial measurements. 161 healthy women with low-risk pregnancies were included after written consent in a prospective longitudinal observational study approved by the Regional Committee of Medical Research Ethics. The participants were examined 3–5 times during the second half of pregnancy using ultrasound imaging and Doppler techniques. Peak systolic velocity (PSV), time averaged maximum velocity (TAV), and Pulsatility Index (PI) was determined. Regression models and multilevel modelling were used to establish means and reference ranges. Terms for calculating conditional reference intervals were also established. Our new reference ranges are based on a total of 566 observations and show increasing velocities throughout pregnancy (Table 1). The interval between the 10th and 90th percentiles widens during the last 10 weeks of pregnancy. The PI reference curve is an inverted U with turning point around 30 weeks. New longitudinal reference ranges of MCA blood velocity and indices differ slightly from previous cross-sectional studies and are recommended as more appropriate for the serial evaluation of the fetus than the existing charts, particularly if conditional percentiles are calculated for the individual measurements. Table 1. Reference ranges presented as percentiles for PI, PSV and TAV of the MCA.
We appreciate the development in the field of obstetric ultrasound recently presented by Gjessing et al. in this Journal1, providing a new method of predicting the day of delivery based on second-trimester biometry. We think it is a valuable study, but have some concerns with regards to the authors' methods. The authors state in the Abstract that their study was based on data collected prospectively. We cannot see that this classification is justified since there is no information that the measurements were taken with the object of developing a new method according to a protocol established before the data collection started. Rather, this study is a retrospective analysis of a population that attended the ultrasound unit either for a routine second-trimester scan or based on a clinical indication. It is not clear whether the study population was in fact unselected. The authors excluded 1935/45 343 (4.3%) because of malformations and excluded another 1137 since they were examined because of possible abnormal fetal growth. However, it can be inferred that a considerable proportion (possibly 10%) of those who were regarded as being eligible for the statistical analysis had one or more repeat scans (36 982 had 41 343 scans). The Norwegian population is only offered one ultrasound scan during pregnancy, on the basis of a consensus recommendation, but the authors have not accounted for the indications for a second measurement or discussed to what extent this might influence the statistics. In Norway, the routine scan is performed between gestational weeks 17 and 20, which is reflected in the numbers of the study: there was a substantial step up in number of participants in this time period (corresponding to a biparietal diameter of 40–50 mm in Table 1). Before this period, ultrasound examinations are commonly done on clinical indication and for risk assessment. By including fetuses at 13–16 weeks of gestation, the authors have based their statistics on an unknown large number of participants with clinical problems. The same could be said for pregnancies examined at 20–24 weeks of gestation; they represent a different population compared with those conventionally scanned at 17–20 weeks. What were the indications for doing the scan outside the conventional 17–20 weeks of gestation, and how were the women distributed in these groups? In a recent prospective study2, 3 we were able to show that for the 10% of fetuses that were most dolichocephalic, the biparietal diameter (BPD) method missed the day of spontaneous birth by − 3.0 days (95% CI, − 4.5 to − 1.4) compared with the head circumference (HC) method's 0.9 days (95% CI, − 0.6 to 2.4): a good reason for contemplating using HC rather than BPD. The midwives trained at the center in Trondheim have been recommended to measure the fronto-occipital diameter in fetuses considered to be dolichocephalic, and to use this information in order to assign an expanded virtual BPD for the calculation of gestational age and day of confinement. We cannot see that the authors have given any account of these fetuses or how this procedure influenced the statistics. Large databases represent advantages when conducting statistical analysis, but carry inherent weaknesses when it comes to controlling the quality of the material. We therefore believe that the authors' new method of calculating the remaining days of pregnancy should be tested in a prospective study. T. Kiserud* , S. L. Johnsen , S. Rasmussen* , * Department of Clinical Medicine, University of Bergen, Bergen, Norway, Department of Obstetrics and Gynecology, Haukeland University Hospital, Bergen, Norway, Medical Birth Registry of Norway, Locus of Registry Based Epidemiology, University of Bergen and the Norwegian Institute of Public Health, Bergen, Norway
