Sonographic measurement of amniotic fluid volume in the first trimester of pregnancy

Amniotic sac diameter reference interval in early pregnancy between 7 and 10 weeks' gestation

OBJECTIVE

To establish a normal reference interval for amniotic sac diameter (ASD) between 7 + 0 and 9 + 6 weeks' gestation and its relative size in relation to gestational sac diameter (GSD) and the embryo crown-rump length (CRL).

METHODS

This was a prospective, cross-sectional study of consecutive women presenting to the Early Pregnancy Unit, University College Hospital, London, UK, between August 2022 and June 2023. We included live, normally sited, singleton pregnancies with a normal 20-week anomaly scan. We collected 120 cases per gestational week, from 7 + 0 to 9 + 6 weeks' gestation, totaling 360 cases. We performed an inter- and intraobserver variability assessment in the measurement of mean ASD in 30 patients. Regression analyses were used to establish reference intervals for GSD and CRL, ASD and CRL, GSD and ASD, and GSD/ASD ratio and CRL. A fitted regression line was calculated, along with a 90% prediction interval and R2 value.

RESULTS

There was good interobserver agreement (mean ± SD difference, 0.007 ± 1.105 mm (95% limits of agreement (LoA), -2.160 to 2.174 mm)) and good intraobserver agreement for Observer A (mean ± SD difference, -0.080 ± 0.741 mm (95% LoA, -1.532 to 1.372 mm)) and Observer B (mean ± SD difference, -0.014 ± 0.919 mm (95% LoA, -1.814 to 1.786 mm)) in the measurement of mean ASD. Regression analyses showed a statistically significant association between each pair of values (P < 0.001 for all). There was a significant quadratic association between mean GSD and CRL (R2 = 56%), mean GSD and ASD (R2 = 60%) and GSD/ASD ratio and CRL (R2 = 68%), and a significant cubic association between mean ASD and CRL (R2 = 90%). The regression equations were used to quantify the values of ASD and GSD/ASD ratios for a range of CRL values and gestational ages.

CONCLUSION

Our study has produced comprehensive reference intervals for amniotic sac size in early pregnancy, which could be used in routine clinical practice. © 2024 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

In utero lung gene transfer using adeno-associated viral and lentiviral vectors in mice

Virus-mediated gene transfer to the fetal lung epithelium holds considerable promise for the therapeutic management of prenatally diagnosed, potentially life-threatening inherited lung diseases. In this study we hypothesized that efficient and life-long lung transduction can be achieved by in utero gene therapy, using viral vectors. To facilitate diffuse entry into the lung, viral vector was injected into the amniotic sac of C57BL/6 mice on embryonic day 16 (term, ∼ 20 days) in a volume of 10 μl. Vectors investigated included those based on adeno-associated virus (AAV) (serotypes 5, 6.2, 9, rh.64R1) and vesicular stomatitis virus G glycoprotein (VSV-G)-pseudotyped HIV-1-based lentivirus (LV). All vectors expressed green fluorescent protein (GFP) under the transcriptional control of various promoters including chicken β-actin (CB) or cytomegalovirus (CMV) for AAV and CMV or MND (myeloproliferative sarcoma virus enhancer, negative control region deleted) for LV. Pulmonary GFP gene expression was detected by fluorescence stereoscopic microscopy and immunohistochemistry for up to 9 months after birth. At equivalent vector doses (mean, 12 × 10(10) genome copies per fetus) three AAV vectors resulted in long-term (up to 9 months) pulmonary epithelium transduction. AAV2/6.2 transduced predominantly cells of the conducting airway epithelium, although transduction decreased 2 months after vector delivery. AAV2/9-transduced cells of the alveolar epithelium with a type 1 pneumocyte phenotype for up to 6 months. Although minimal levels of GFP expression were observed with AAV2/5 up to 9 months, the transduced cells immunostained positive for F480 and were retrievable by bronchoalveolar lavage, confirming an alveolar macrophage phenotype. No GFP expression was observed in lung epithelial cells after AAV2/rh.64R1 and VSV-G-LV vector-mediated gene transfer. We conclude that these experiments demonstrate that prenatal lung gene transfer with AAV vectors engineered to target pulmonary epithelial cells may provide sustained long-term levels of transgene expression, supporting the therapeutic potential of prenatal gene transfer for the treatment of congenital lung diseases.

Early intra-amniotic gene transfer using lentiviral vector improves skin blistering phenotype in a murine model of Herlitz junctional epidermolysis bullosa

Mutations of the LAMB3 gene cause a lethal form of junctional epidermolysis bullosa (JEB). We hypothesized that early intra-amniotic gene transfer in a severe murine model of JEB would improve or correct the skin phenotype. Time-dated fetuses from heterozygous LAMB3(IAP) breeding pairs underwent ultrasound guided intra-amniotic injection of lentiviral vector encoding the murine LAMB3 gene at embryonic day 8 (E8). Gene expression was monitored by immunohistochemistry. The transgenic laminin-β3 chain was shown to assemble with its endogenous partner chains, resulting in detectable amounts of laminin-332 in the basement membrane zone of skin and mucosa. Ultrastructually, the restoration of ∼60% of hemidesmosomal structures was also noted. Although we could correct the skin phenotype in 11.9% of homozygous LAMB3(IAP) mice, none survived beyond 48 h. However, skin transplants from treated E18 homozygous LAMB3(IAP) fetuses maintained normal appearance for 6 months with persistence of normal assembly of laminin-332. These results demonstrate for the first time long-term phenotypic correction of the skin pathology in a severe model of JEB by in vivo prenatal gene transfer. Although survival remained limited due to the limitations of this mouse model, this study supports the potential for treatment of JEB by prenatal gene transfer.

Reference intervals of gestational sac, yolk sac and embryo volumes using three-dimensional ultrasound

OBJECTIVES

To create reference intervals of gestational sac volume (GSV), yolk sac volume (YSV), embryo volume (EV), crown-rump length (CRL) and gestational sac diameter (GSD) in the first trimester of pregnancy using three-dimensional ultrasound.

METHODS

Women in the first trimester of pregnancy were invited to participate in the study. Inclusion criteria were well-established dates, and that the women were non-smokers and healthy, without any medical disorders. Three-dimensional ultrasound volumetric data (GSV, YSV, EV) were collected together with standard two-dimensional measurements of CRL and GSD. For each measurement separate regression models were fitted to estimate the mean and SD at each gestational age. The 5(th), 50(th) and 95(th) centiles were derived using a combination of these regression models.

RESULTS

One hundred and sixty-six women at between 6 and 12 weeks' gestation were scanned once. The mean ( +/- SD) maternal age was 29.4 ( +/- 5) years. There were no miscarriages and no congenital abnormalities were noted. Mean gestational age at delivery was 39.3 ( +/- 1.4) weeks and mean birth weight was 3.3 ( +/- 0.4) kg. The CRL centiles fitted a cubic model and the GSD centiles fitted a linear model. The centiles for YSV fitted a quadratic model on the modified log-transformed data. The centiles for GSV and EV were modeled using quantile regression.

CONCLUSION

Reference intervals and centile charts for first-trimester GSV, YSV and EV have been created in addition to CRL and GSD using rigorous methodology.

Nomogram of amniotic fluid volume at 7 to 10+6 weeks of pregnancy by three-dimensional ultrasonography using the rotational method (VOCAL)

PURPOSE

To establish normative data for amniotic fluid volume (AFV) between 7 and 10+6 weeks gestation using three-dimensional ultrasonography (3DUS).

METHODS

A cross-sectional study involving 74 normal pregnancies was performed to assess AFV. All measurements were performed using an endocavitary volumetric transducer. The VOCAL (virtual organ computer-aided analysis) method was used for volumetric calculations, with a 30 degrees rotation angle. The AFV was obtained subtracting the embryonic volume from the amniotic sac volume. To analyze the correlation between AFV and gestational age, regression models were constructed and adjustments were made using the determination coefficient (R2). The following AFV values were obtained for each week: mean, median, standard deviation, minimum and maximum. The method proposed by Royston and Wright was used to calculate the reference intervals according to crown-rump length (CRL).

RESULTS

Mean AFV increased from 3.97 cm3 (range 1.17-10.97 cm3) at 7 to 7+6 weeks to 23.33 cm3 (ranging from 11.93 to 32.41 cm3) at 10 to 10+6 weeks of pregnancy. There was a significant correlation between AFV and gestational age (R2=0.635) and between AFV and CRL (R2=0.756). Mean AFV increased from 7.81 cm3 (ranging from 0.18 to 15.43 cm3) to 50.28 cm3 (range 16.49-84.07 cm3) for CRL between 12 and 40 mm.

CONCLUSIONS

Reference limits for AFV using 3DUS were generated for pregnancies between 7 and 10+6 weeks according to CRL.

Amniotic fluid volumetry by three-dimensional ultrasonography during the first trimester of pregnancy

In a longitudinal prospective study, we quantitated the amniotic fluid volume (AFV) of 25 normal fetuses by endovaginal 3-D ultrasonography (3D-US) from the 8th to the 11th week of pregnancy. AFV by 3D-US was obtained by subtracting the volumetric measurement of the embryo (EV) from the amniotic sac volume (ASV). EV and ASV were obtained by virtual organ computer-aided analysis (VOCAL), using 6 degrees of rotation. AFV increased from 5.75 to 42.96 cm(3) from the 8th to the 11th week (ANOVA, p < 0.05), with a correlation between gestational age and AFV (p < 0.001, r(2) = 98.1%). We conclude that there was an increase in AFV assessed by 3D-US. The AFV values for normal fetuses can be used for comparison with those detected in pregnancies with risk of fetal loss.

Sonographic assessment of amniotic fluid volume between 11 and 24 weeks of gestation: construction of reference intervals related to gestational age

OBJECTIVE

At present, most of the methods for sonographic assessment of amniotic fluid volume are unreliable in the second trimester of pregnancy, or else they do not present nomograms related to gestational age.

DESIGN

The aim of this prospective cross-sectional study was to construct normal reference ranges of four ultrasound parameters for the evaluation of amniotic fluid volume which could be applied in the second trimester. For these parameters we calculated normal curve limits suitable for use in clinical practice.

SUBJECTS

From a population of normal pregnant women between the 12th and the 24th weeks of gestation undergoing a routine ultrasound examination during 1997 at our institute, 273 were found to be suitable for the study, after the exclusion of all cases which presented any feto-maternal pathology or complications up to the 24th week.

METHODS

The largest 'amniotic pocket' in a vertical direction, free of small fetal parts and umbilical cord, was measured: the maximum vertical and transverse diameters were measured on the same scan; the mean diameter and the product of the two diameters were calculated. The 'mean amniotic fluid diameter', the 'two-diameter pocket', the 'largest vertical pocket' and the 'largest transverse pocket' were the four sonographic parameters considered.

RESULTS

The four parameters correlated well with gestational week and with the biparietal diameter; the normal reference intervals and normal curve were then calculated. All these parameters were found to have good intra- and interoperative reproducibility.

CONCLUSIONS

We conclude that the use of an ultrasound semiquantitative method based on the measurement of a single amniotic fluid pocket and involving normal reference intervals according to gestational age could improve the early diagnosis of amniotic fluid variations during the second trimester, although this has yet to be confirmed by extensive clinical trials.

Measurements of organ volume by ultrasonography

In a clinical context, measurements of organ volume are often performed in the diagnosis and follow-up of patients with a variety of diseases. Ultrasonography is a cheap, widely available and non-hazardous imaging modality to use for estimation of volumes, and a range of two- and three-dimensional methods have emerged to accomplish this task. This paper reviews some of the ultrasound methods available in cardiology, gastroenterology, nephrology/urology and gynaecology/obstetrics. Using two-dimensional (2D) ultrasound, the simplest method of calculating the volume of an organ is based on the multiplication of three diameters perpendicular to each other. These 2D methods are often based on geometrical assumptions which may introduce significant errors in volume estimation. Therefore, volume estimation based on three-dimensional (3D) ultrasound has been developed to increase accuracy and precision. At present, the process of making 3D images based on ultrasonography is divided into five steps: data acquisition, data digitization, data storage, data processing and data display. In conclusion, ultrasonography is a useful and reliable tool to calculate volumes of organs. In particular, 3D ultrasonography seems promising in this respect and appears to be superior to 2D ultrasonography in accuracy and precision in volume measurements.