Myometrial thickness according to uterine site, gestational age and prior cesarean delivery

Association between placental location and cord insertion site with pre-eclampsia: a retrospective cohort study

OBJECTIVE

The relationship between placental location in pregnancies without previa and adverse pregnancy outcomes has not been well studied. Additionally, the impact of abnormal cord insertion sites remains controversial. Therefore, the objective of this study was to explore the adverse outcomes associated with placental location and abnormal cord insertion in nulliparous women and to assess their impact on pregnancy outcomes.

METHODS

This retrospective cohort study was conducted at a single tertiary hospital between January 2019 and June 2022. The study included nulliparous women with singleton pregnancies who delivered live infants and had available data on placental location and umbilical cord insertion site from a second- or third-trimester ultrasound. Placental location was categorized as anterior or posterior using transabdominal ultrasonography. The association between placental location/cord insertion site and pre-eclampsia was evaluated using multivariate logistic regression analysis. We compared the area under the curve to evaluate the impact of placental location and cord insertion site on pre-eclampsia.

RESULTS

A total of 2219 pregnancies were included in the study. Pre-eclampsia occurred significantly more frequently in the anterior group than in the posterior group (8.21% vs. 3.04%, p < .001). In multivariate analysis investigating the association between placental location and pre-eclampsia, anterior placenta and marginal cord insertion showed increased odds ratios for pre-eclampsia of 3.05 (95% confidence interval [CI] 1.68-6.58) and 3.64 (95% CI 1.90-6.97), respectively. Receiver operating characteristic (ROC) curves were constructed to predict pre-eclampsia using independent factors from multivariate analyses. Model I, including maternal age, pre-pregnancy body mass index, in vitro fertilization, chronic hypertension, overt diabetes, kidney disease, and hematologic diseases, achieved an area under the ROC curve of 0.70 (95% CI 0.65-0.75). Adding cord insertion site and placental location to the model (Model II) improved its predictive performance, resulting in an area under the ROC curve of 0.749 (95% CI 0.70-0.79, p = .02).

CONCLUSIONS

Anterior placenta and marginal cord insertion were associated with an increased risk of pre-eclampsia. Further studies on prospective cohorts are necessary to validate these findings.

Uterus and cervix anatomical changes and cervix stiffness evolution throughout pregnancy

The coordinated biomechanical performance, such as uterine stretch and cervical barrier function, within maternal reproductive tissues facilitates healthy human pregnancy and birth. Quantifying normal biomechanical function and detecting potentially detrimental biomechanical dysfunction (e.g., cervical insufficiency, uterine overdistention, premature rupture of membranes) is difficult, largely due to minimal data on the shape and size of maternal anatomy and material properties of tissue across gestation. This study quantitates key structural features of human pregnancy to fill this knowledge gap and facilitate three-dimensional modeling for biomechanical pregnancy simulations to deeply explore pregnancy and childbirth. These measurements include the longitudinal assessment of uterine and cervical dimensions, fetal weight, and cervical stiffness in 47 low-risk pregnancies at four time points during gestation (late first, middle second, late second, and middle third trimesters). The uterine and cervical size were measured via 2-dimensional ultrasound, and cervical stiffness was measured via cervical aspiration. Trends in uterine and cervical measurements were assessed as time-course slopes across pregnancy and between gestational time points, accounting for specific participants. Patient-specific computational solid models of the uterus and cervix, generated from the ultrasonic measurements, were used to estimate deformed uterocervical volume. Results show that for this low-risk cohort, the uterus grows fastest in the inferior-superior direction from the late first to middle second trimester and fastest in the anterior-posterior and left-right direction between the middle and late second trimester. Contemporaneously, the cervix softens and shortens. It softens fastest from the late first to the middle second trimester and shortens fastest between the late second and middle third trimester. Alongside the fetal weight estimated from ultrasonic measurements, this work presents holistic maternal and fetal patient-specific biomechanical measurements across gestation.

A Sustainable Translational Sheep Model for Planned Cesarean Delivery of Contraction-Free Ewes

We evaluated whether the sheep constitutes a useful translational model to evaluate anatomical and surgical aspects of cesarean delivery (CD) from a human medical perspective with the aim of both maternal and neonatal well-being. Our hypothesis was that CD in contraction-free ewes is not associated with major complications. Primary endpoint was the transferability of anatomical conditions and surgical techniques of CD from the ewe to the human. Secondary endpoints were maternal and fetal survival, occurrence of retained fetal membranes, metritis, mastitis, or wound infections. Forty-eight Merino ewes were delivered by CD after 95% gestation (142-144 days). Both ewes and newborn lambs were cared for intensively after the delivery. Ovine uterine anatomy during CD appeared slightly different but comparable to the human uterus. Uterine incisions were mostly performed in the uterine horns, not in the uterine corpus. The ovine uterine wall is thinner than in humans. All ewes survived without any major complications. Seventy-seven (88.5%) out of 87 live-born lambs survived without any complications. The contraction-free ewe constitutes an appropriate and safe model to evaluate anatomical and surgical aspects of CD from a human medical perspective. We present a step-by-step manual for successfully planned cesarean delivery for sheep including the perioperative management illustrated with photographs and a five-minute video. With adequate planning and a reasonable number of staff, it is possible to safeguard both maternal and neonatal survival. This sustainable translational medicine model offers additional potential for the offspring to be used for further research studies (e.g., transgenerational inheritance research).

Risk factors of MRI findings for predicting patient outcomes of placenta accreta spectrum and placenta previa after prophylactic balloon occlusion of the internal iliac artery

PURPOSE

Our study aimed to identify the risk factors of magnetic resonance imaging (MRI) findings for predicting patient outcomes of placenta accreta spectrum (PAS) and placenta previa after prophylactic balloon occlusion of the internal iliac artery (PBOIIA).

MATERIALS AND METHODS

This retrospective analysis was performed using the clinical records of 46 patients diagnosed with PAS and placenta previa who underwent PBOIIA during caesarean section (CS). The possible clinical risk factors for adverse maternal outcomes were evaluated by consulting patients' clinical records. The inclusion criteria for the massive bleeding group were as follows: estimated blood loss (EBL) > 2500 mL, packed red blood cell (pRBC) transfusion (>4 units), and need for hysterectomy or transcatheter arterial embolization after delivery. The MRI features were compared between the massive and non-massive bleeding groups.

RESULTS

Patients in the massive bleeding group (n = 22) had a significantly longer operation time (p < 0.001), more EBL (p < 0.001), more pRBC transfusions (p < 0.001), and a prolonged postoperative hospital stay (p < 0.05). MRI features showed a T2 dark bands, placenta bulge, and abnormal blood vessels in the placental bed more frequently in the massive bleeding group (p < 0.05). In the multiple logistic regression analysis, T2 dark bands (odds ratio 9.1, p = 0.048) and placental bulge (odds ratio 5.1, p = 0.014) remained statistically significant.

CONCLUSION

T2 dark bands and placental bulges observed on an MRI can predict adverse maternal outcomes in patients with PAS and placenta previa undergoing PBOIIA. If these findings are observed on a preoperative MRI, effective management strategies should be prepared for the possibility of massive hemorrhage during CS.

Association between lower uterine wall thickness measured at 18-22 weeks of gestation and risk of Preterm Birth: a prospective cohort study

Background

Preterm labour prediction has been relied on history of previous preterm birth and cervical length of current pregnancy. However, universal cervical length measurement has some limitation. We aim to find a surrogate marker of cervical length to close the gap in preterm prevention program and lower uterine wall thickness seems promising. We generate the nomogram of lower uterine wall thickness during 18–22 weeks of gestation and evaluate the accuracy of LUW thickness as a predictor of preterm delivery before 37 weeks.

Methods

This prospective cohort study included 524 Thai singleton pregnant women at 18–22 weeks of gestation between November 2016 and October 2017. After signing informed consent, transabdominal ultrasonography was performed to examine fetal anatomical structures and to measure LUW thickness. The results were blinded to the caregivers. The outcomes of all pregnancies were followed. The LUW thickness at 10th percentiles was established and was correlated with the outcomes of pregnancy. The performance of LUW thickness at 10th percentile as a predictor of preterm delivery was calculated. The intra-observer and inter-observer reliability of measurement were assessed by intraclass correlation coefficient and Bland-Altman plot.

Results

Of the 524 pregnant women, 64 (12.2%) delivered before 37 weeks of gestation. The reference value of lower uterine wall thickness at 18–22 weeks was established. Mean and 10th percentile of LUW thickness were 6.2 and 4.5 mm respectively. The inter-observer and intra-observer variation of measurement were small (intraclass correlation coefficient = 0.926 and 0.989 respectively). Using LUW thickness at less than 4.5 mm as a predictor of preterm delivery, we found a 2.37 folds increased risk of preterm delivery after adjustment of other factors (p = 0.037). Sensitivity, specificity, positive predictive value and negative predictive value were 14% (95% CI: 6.64–25.02), 92.8% (95% CI: 90.06–95.12), 22.5% (95% CI: 12.66–36.76) and 88% (95% CI: 86.92–89.08) respectively.

Conclusions

The measurement of LUW thickness by transabdominal ultrasonography is feasible and reproducible. The risk of delivery before 37 weeks of gestation is increased significantly if the LUW thickness at 18–22 weeks is less than 4.5 mm.

Trial registration

The study protocol was approved by institutional ethical committee (COA No. Si 657/2016).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-022-04902-w.

Longitudinal ultrasonic dimensions and parametric solid models of the gravid uterus and cervix

Tissue mechanics is central to pregnancy, during which maternal anatomic structures undergo continuous remodeling to serve a dual function to first protect the fetus in utero while it develops and then facilitate its passage out. In this study of normal pregnancy using biomechanical solid modeling, we used standard clinical ultrasound images to obtain measurements of structural dimensions of the gravid uterus and cervix throughout gestation. 2-dimensional ultrasound images were acquired from the uterus and cervix in 30 pregnant subjects in supine and standing positions at four time points during pregnancy (8-14, 14-16, 22-24, and 32-34 weeks). Offline, three observers independently measured from the images of multiple anatomic regions. Statistical analysis was performed to evaluate inter-observer variance, as well as effect of gestational age, gravity, and parity on maternal geometry. A parametric solid model developed in the Solidworks computer aided design (CAD) software was used to convert ultrasonic measurements to a 3-dimensional solid computer model, from which estimates of uterine and cervical volumes were made. This parametric model was compared against previous 3-dimensional solid models derived from magnetic resonance frequency images in pregnancy. In brief, we found several anatomic measurements easily derived from standard clinical imaging are reproducible and reliable, and provide sufficient information to allow biomechanical solid modeling. This structural dataset is the first, to our knowledge, to provide key variables to enable future computational calculations of tissue stress and stretch in pregnancy, making it possible to characterize the biomechanical milieu of normal pregnancy. This vital dataset will be the foundation to understand how the uterus and cervix malfunction in pregnancy leading to adverse perinatal outcomes.

The use of sonographic myometrial thickness measurements for the prediction of time from induction of labor to delivery

BACKGROUND

Several attempts have been made to find tools for the prediction of successful induction of labor. Sonographic myometrial thickness has not yet been investigated regarding its use as a clinical tool for the course of labor induction.

OBJECTIVE

To evaluate the role of sonographic measurement of myometrial thickness in the prediction of the time interval to successful vaginal delivery after induction of labor.

STUDY DESIGN

A prospective study was conducted including term singleton pregnancies with a vertex presentation designated for balloon induction at 38-42 weeks gestation. Prior to induction, abdominal sonographic myometrial thickness was assessed at five locations: lower uterine segment (above and below the reflection of the urinary bladder), mid-anterior wall, fundus and posterior uterine wall. Induction of labor was then carried out with a trans-cervical Foley catheter that was substituted with intravenous oxytocin after balloon expulsion. The parameters assessed were successful induction of labor resulting in a vaginal delivery and the time interval from balloon insertion to balloon expulsion, the time interval from initiation of oxytocin administration to delivery and the total time from balloon insertion to delivery.

RESULTS

Fifty-two women were recruited to the study. Indications for labor induction were: post-date pregnancy (48.1%), gestational diabetes mellitus (19.2%), oligohydramnios (11.5%), gestational hypertensive disorders (5.8%) and other indications (15.4%). Vaginal delivery was achieved in 46 patients (88.5%). A statistically significant correlation was found between fundal and posterior uterine wall myometrial thickness and time from induction to balloon expulsion (r = 0.36, p = 0.03; r = - 0.35, p = 0.05, respectively). This correlation remained significant in a multivariate logistic regression model controlling for confounders. A correlation between myometrial thickness and the total time from induction to delivery was not statistically significant.

CONCLUSION

Myometrial fundal and posterior uterine wall thickness in women undergoing labor induction with a balloon catheter was found to be correlated with the interval from balloon insertion to expulsion. Our findings support further investigations into the use of sonographic myometrial thickness as part of the assessment prior to induction of labor.

Anterior placenta previa in the mid-trimester of pregnancy as a risk factor for neonatal respiratory distress syndrome

This study investigated whether anterior placenta previa in the second trimester is associated with neonatal respiratory distress syndrome (RDS). The neonates delivered by 2067 women between 2007 and 2015 were evaluated for the presence of RDS through birth records. The location of the placenta and the presence of placenta previa during the second and third trimesters were assessed and recorded. Demographic, prenatal, and perinatal records were reviewed. Anterior placenta previa in the second and third trimesters was correlated with RDS. Infants with lower gestational ages and birth weights had higher rates of RDS. Multivariate logistic regression analysis identified a significant association between anterior placenta previa in the second trimester and neonatal RDS. Anterior placenta previa in the second trimester is associated with neonatal RDS. Obstetricians should be aware that anterior placenta previa detected during the second trimester, irrespective of whether the placenta will migrate in the third trimester, may be an independent risk factor for neonatal RDS.

Spontaneous uterine rupture and surgical repair at 21 weeks gestation with progression to live birth: a case report

BACKGROUND

Uterine rupture in the non-laboring uterus is a rare occurrence, which can lead to significant morbidity and mortality for the mother and fetus. Management of this presentation is complex at pre-viable gestations.

CASE PRESENTATION

A 35 year old primigravid woman with multiple previous myomectomies presented with spontaneous complete thickness uterine rupture at 21 weeks gestation. A 10 cm myometrial defect and iatrogenic amniotomy were surgically corrected with fetal preservation. This led to pregnancy continuation to 32 weeks gestation when elective cesarean delivery resulted in excellent neonatal outcome.

CONCLUSIONS

Early surgical diagnosis, multidisciplinary team approach, iatrogenic amniotomy and continuous two-layer myometrial closure were factors that contributed to pregnancy prolongation in this large myometrial rupture.

Association of Placental Jets and Mega-Jets With Reduced Villous Density

Spiral arteries (SAs) lie at the interface between the uterus and placenta, and supply nutrients to the placental surface. Maternal blood circulation is separated from the fetal circulation by structures called villous trees. SAs are transformed in early pregnancy from tightly coiled vessels to large high-capacity channels, which is believed to facilitate an increased maternal blood flow throughout pregnancy with minimal increase in velocity, preventing damage to delicate villous trees. Significant maternal blood flow velocities have been theorized in the space surrounding the villi (the intervillous space, IVS), particularly when SA conversion is inadequate, but have only recently been visualized reliably using pulsed wave Doppler ultrasonography. Here, we present a computational model of blood flow from SA openings, allowing prediction of IVS properties based on jet length. We show that jets of flow observed by ultrasound are likely correlated with increased IVS porosity near the SA mouth and propose that observed mega-jets (flow penetrating more than half the placental thickness) are only possible when SAs open to regions of the placenta with very sparse villous structures. We postulate that IVS tissue density must decrease at the SA mouth through gestation, supporting the hypothesis that blood flow from SAs influences villous tree development.

A Parameterized Ultrasound-Based Finite Element Analysis of the Mechanical Environment of Pregnancy

Preterm birth is the leading cause of childhood mortality and can lead to health risks in survivors. The mechanical functions of the uterus, fetal membranes, and cervix have dynamic roles to protect the fetus during gestation. To understand their mechanical function and relation to preterm birth, we built a three-dimensional parameterized finite element model of pregnancy. This model is generated by an automated procedure that is informed by maternal ultrasound measurements. A baseline model at 25 weeks of gestation was characterized, and to visualize the impact of cervical structural parameters on tissue stretch, we evaluated the model sensitivity to (1) anterior uterocervical angle, (2) cervical length, (3) posterior cervical offset, and (4) cervical stiffness. We found that cervical tissue stretching is minimal when the cervical canal is aligned with the longitudinal uterine axis, and a softer cervix is more sensitive to changes in the geometric variables tested.

Biomechanics of the human uterus

The appropriate biomechanical function of the uterus is required for the execution of human reproduction. These functions range from aiding the transport of the embryo to the implantation site, to remodeling its tissue walls to host the placenta, to protecting the fetus during gestation, to contracting forcefully for a safe parturition and postpartum, to remodeling back to its nonpregnant condition to renew the cycle of menstruation. To serve these remarkably diverse functions, the uterus is optimally geared with evolving and contractile muscle and tissue layers that are cued by chemical, hormonal, electrical, and mechanical signals. The relationship between these highly active biological signaling mechanisms and uterine biomechanical function is not completely understood for normal reproductive processes and pathological conditions such as adenomyosis, endometriosis, infertility and preterm labor. Animal studies have illuminated the rich structural function of the uterus, particularly in pregnancy. In humans, medical imaging techniques in ultrasound and magnetic resonance have been combined with computational engineering techniques to characterize the uterus in vivo, and advanced experimental techniques have explored uterine function using ex vivo tissue samples. The collective evidence presented in this review gives an overall perspective on uterine biomechanics related to both its nonpregnant and pregnant function, highlighting open research topics in the field. Additionally, uterine disease and infertility are discussed in the context of tissue injury and repair processes and the role of computational modeling in uncovering etiologies of disease. WIREs Syst Biol Med 2017, 9:e1388. doi: 10.1002/wsbm.1388 For further resources related to this article, please visit the WIREs website.

Measurements of the lower uterine segment during gestation

PURPOSE

To establish normal values for the lower uterine segment (LUS) thickness and to recognize factors that may affect these values.

METHODS

In this cross-sectional study, we measured the LUS thickness in women between 11 and 41 weeks gestation. Women with placental abnormalities and fetal anomalies were excluded. Fetal weight, location of placental implantation, and cervical length were estimated. The LUS was examined to identify the thinnest zone and evaluated using the transvaginal approach with an empty urinary bladder. Full LUS thickness was measured with a caliper at the inner surface of the posterior bladder wall and another caliper at the interface between the amniotic fluid and the decidua. The myometrium was measured with the first caliper at the interface between the amniotic fluid and the deciduas and the second between the bladder wall and the myometrium. Normal values for the LUS were established throughout gestation, and correlations between the LUS gestational age, fetal weight, previous cesarean section, and other parameters were examined.

RESULTS

Overall, 350 women were included in our study. Median parity was 1 (0-6) and the majority (62%, 218/350) of women have not had a previous cesarean section. The LUS thickness inversely correlated with gestational week (Pearson's r = -0.11, p < 0.03). When stratifying the linear regression model to women with and without a history of a previous cesarean section, it was demonstrated that gestational age was moderately correlated with LUS only in the second group of patients (Pearson's r = -0.16, p = 0.1 and Pearson's r = -0.47, p < 0.0001, respectively). During the post term period, patients who had had a previous cesarean section had significantly thinner LUS compared with patients who had not had a previous cesarean section (46 mm ± 20 versus 59 mm ± 20, p = 0.002, respectively). Neither parity nor the number of previous cesarean sections were found to correlate with the thickness of the LUS (p > 0.05). Multivariate linear regression (R(2) = 0.215, F(2, 63) = 9.021, p < 0.001) demonstrated that both gestational week (β = -0.13, p < 0.04) and cesarean section (β = -0.01, p < 0.0001) were independent factors associated with the thickness of the LUS; for every 1 week increase in gestational week, there was a 1.3 mm decrease in the total thickness of the LUS CONCLUSIONS: We have established reference ranges for LUS thickness throughout gestation. The LUS thickness decreases throughout gestation in singleton pregnancies and is significantly thinner in postterm period pregnant women with a previous cesarean section.

[Management of pregnancies with a previous cesarean]

The cesarean rate in France has reached 21% in 2010. With a maintained fertility rate, management of a pregnant woman with a previous caesarean scar is becoming a daily situation for most obstetrical teams. Considering the small rate of vaginal birth after cesarean (VBAC), we will try to establish an up-to-date review of the benefits and risks of encouraging trial of VBAC. This information can help professionals provide adequate counselling women or couples.

Predicting uterine rupture in women undergoing trial of labor after prior cesarean delivery

Uterine rupture is the most serious complication for women undergoing trial of labor (TOL) after prior cesarean delivery. While rates of uterine rupture vary significantly according to a variety of clinically associated risk factors, the absolute risk for this complication ranges between 0.5 and 4 percent. Previous vaginal delivery and prior successful vaginal birth after cesarean delivery confer the lowest risk of rupture on women attempting TOL. In contrast, multiple prior cesareans, short interpregnancy interval, single layer uterine closure, prior preterm cesarean, labor induction and augmentation have all been suggested in some studies as factors which may increase the rate of uterine rupture. While considering these risk factors is important in counseling women regarding childbirth following cesarean delivery, the infrequency of uterine rupture coupled with relatively weak associations for most risk factors has prevented the development of an accurate prediction tool for uterine rupture. Preliminary studies suggest that sonographic evaluation of the uterine scar may hold some promise for identifying women at risk.

Chronic fetal and maternal instrumentation in pregnant sheep: effect on gestation length and birthweight

The objective was to compare gestation length in chronically instrumented (laboratory) pregnant sheep (n = 131) and in the breeding flock (n = 476) that provided the experimental sheep. In the breeding flock, gestation length was normally distributed and varied between 141 and 151 days (mean = 147 +/- 0.1 days). In the laboratory sheep, gestation length varied between 128 and 151 days (mean = 142 +/- 1 day), and was bimodal, with 35.9% delivering preterm (<141 days). To examine potential factors that contributed to the preterm birth, a severity score was used, which comprised surgery characteristics, number of experiments and maternal or fetal complications. There was a significant inverse linear relationship (P < 0.001) between the total severity score and gestation length. The median values for the surgical (15 v. 12), overall complication (6 v. 2), maternal complication (2 v. 0) and fetal complication (2 v. 2) components were significantly greater in the preterm compared with the term groups. There was no relationship between fetal number and gestation length in either group. It is concluded that in chronic pregnant sheep preparations, there is a significant incidence of preterm birth and that this is associated with the severity of the surgical intervention and with several maternal and fetal complications.