Morbidly Adherent Placenta: Ultrasound Assessment and Supplemental Role of Magnetic Resonance Imaging

Use of super resolution reconstruction MRI for surgical planning in Placenta accreta spectrum disorder: Case series

INTRODUCTION

Comprehensive imaging using ultrasound and MRI of placenta accreta spectrum (PAS) aims to prevent catastrophic haemorrhage and maternal death. Standard MRI of the placenta is limited by between-slice motion which can be mitigated by super-resolution reconstruction (SRR) MRI. We applied SRR in suspected PAS cases to determine its ability to enhance anatomical placental assessment and predict adverse maternal outcome.

METHODS

Suspected PAS patients (n = 22) underwent MRI at a gestational age (weeks + days) of (32+3±3+2, range (27+1-38+6)). SRR of the placental-myometrial-bladder interface involving rigid motion correction of acquired MRI slices combined with robust outlier detection to reconstruct an isotropic high-resolution volume, was achieved in twelve. 2D MRI or SRR images alone, and paired data were assessed by four radiologists in three review rounds. All radiologists were blinded to results of the ultrasound, original MR image reports, case outcomes, and PAS diagnosis. A Random Forest Classification model was used to highlight the most predictive pathological MRI markers for major obstetric haemorrhage (MOH), bladder adherence (BA), and placental attachment depth (PAD).

RESULTS

At delivery, four patients had placenta praevia with no abnormal attachment, two were clinically diagnosed with PAS, and six had histopathological PAS confirmation. Pathological MRI markers (T2-dark intraplacental bands, and loss of retroplacental T2-hypointense line) predicting MOH were more visible using SRR imaging (accuracy 0.73), in comparison to 2D MRI or paired imaging. Bladder wall interruption, predicting BA, was only easily detected by paired imaging (accuracy 0.72). Better detection of certain pathological markers predicting PAD was found using 2D MRI (placental bulge and myometrial thinning (accuracy 0.81)), and SRR (loss of retroplacental T2-hypointense line (accuracy 0.82)).

DISCUSSION

The addition of SRR to 2D MRI potentially improved anatomical assessment of certain pathological MRI markers of abnormal placentation that predict maternal morbidity which may benefit surgical planning.

Factors Limiting Magnetic Resonance Imaging Diagnosis of Placenta Accreta Spectrum

OBJECTIVE

Placenta accreta spectrum (PAS) disorders are characterized by an abnormal adherence of the placenta to the uterine myometrium. Magnetic resonance imaging (MRI) is an important adjunct in antenatal diagnosis. We sought to determine if there are patient and MRI characteristics that limit the accuracy of PAS diagnosis and degree of invasion.

STUDY DESIGN

We conducted a retrospective cohort analysis of patients who were evaluated for PAS by MRI from January 2007 to December 2020. Patient characteristics evaluated included number of prior cesarean deliveries, history of dilation and curettage (D&C) or dilation and evacuation (D&E), short interval pregnancy less than 18 months, and delivery body mass index (BMI). All patients were followed until delivery and MRI diagnosis was compared with final histopathology.

RESULTS

Of the 353 patients with suspected PAS, 152 (43%) underwent MRI evaluation and were included in the final analysis. In patients who underwent MRI evaluation, 105 (69%) had confirmed PAS on pathology. Patient characteristics were similar between groups and not associated with accuracy of MRI diagnosis. MRI was accurate in diagnosing PAS and the associated degree of invasion in 83 (55%) patients. Accuracy was associated with lacunae (8 vs. 0%, p = 0.02), abnormal bladder interface (25 vs. 6%, p = 0.002), and T1 hyperintensity (13 vs. 1%, p = 0.002). Of the 69 (45%) patients in whom MRI was inaccurate, overdiagnosis was seen in 44 (64%) patients and underdiagnosis in 25 (36%) patients. Overdiagnosis was significantly associated with dark T2 bands (45 vs. 22%, p = 0.005). Underdiagnosis was associated with earlier gestational age at MRI (28 vs. 30 weeks, p = 0.049) and lateral placentation (16 vs. 2.4%, p = 0.025).

CONCLUSION

Patient factors did not change MRI accuracy of PAS diagnosis. MRI is associated with a significant overdiagnosis of PAS when dark T2 bands are present, and underdiagnose PAS when performed earlier in gestation or when lateral placentation is present.

KEY POINTS

· Patient factors are not associated with MRI accuracy of PAS diagnosis.. · MRI overdiagnoses PAS invasion when there are dark T2 bands.. · MRI underdiagnoses PAS invasion when performed earlier in gestation.. · Underdiagnosis of PAS is associated with lateral placentation..

Developments in functional imaging of the placenta

The placenta is both the literal and metaphorical black box of pregnancy. Measurement of the function of the placenta has the potential to enhance our understanding of this enigmatic organ and serve to support obstetric decision making. Advanced imaging techniques are key to support these measurements. This review summarises emerging imaging technology being used to measure the function of the placenta and new developments in the computational analysis of these data. We address three important examples where functional imaging is supporting our understanding of these conditions: fetal growth restriction, placenta accreta, and twin-twin transfusion syndrome.

Placenta accreta spectrum: the pattern and character of intraplacental blood flow by color and spectral Doppler

PURPOSE

To characterize intraplacental blood flow patterns in placenta accreta spectrum (PAS) with color and spectral Doppler imaging.

METHODS

Thirty-two patients at risk for PAS underwent ultrasound imaging with both color and spectral Doppler. The placenta was inspected for areas of vascularity by color Doppler, particularly within the lower uterine segment. Spectral Doppler waveforms were obtained from these vessels and categorized as either intraplacental or subplacental (myometrial), venous or arterial, fetal or maternal (based on heart rate). Arterial waveforms were measured for heart rate, peak systolic velocity, end diastolic velocity, and resistive index. Statistical comparisons were made between cases with and without PAS using Fisher exact tests (categorical variables) and Mann-Whitney U tests (numerical indices). Interobserver agreement was characterized with kappa coefficients.

RESULTS

At delivery, there were 19 cases with PAS and 13 without PAS. On ultrasound studies, clustered intraplacental vascularity was found in the lower uterine segment in 66% of cases (95% of PAS cases and 23% cases without PAS; p < 0.0001). Maternal arterial waveforms were found within the vascular cluster in 84% of PAS cases and 15% of cases without PAS (p < 0.0001). A traversing fetal artery was found within the vascular cluster in 56% of cases (84% PAS cases and 15% cases without PAS; p = 0.001). Venous waveforms were found in 84% of PAS cases and 15% of cases without PAS. Interobserver agreement was good to excellent.

CONCLUSION

Intraplacental blood flow pattern in PAS is characterized by an intraplacental vascular cluster containing low-resistance maternal arterial flow and transplacental fetal arteries.

The maximum length of T2-dark intraplacental bands may help predict intraoperative haemorrhage in pregnant women with placenta accreta spectrum (PAS)

PURPOSE

To investigate the relationship between the maximum length of T2-dark intraplacental bands (MLTIB) and intraoperative haemorrhage in pregnant women with placenta accreta spectrum (PAS).

METHODS

Between February 2018 and February 2021, 86 pregnant women with PAS who delivered in Taizhou Hospital of Zhejiang Province and underwent preoperative magnetic resonance imaging (MRI) examination were retrospectively recruited. The presence of T2-dark intraplacental bands, placental/uterine bulge, loss of retroplacental T2-hypointense line, myometrial thinning, bladder wall interruption, focal exophytic mass, and abnormal vascularization of placental bed were recorded, and the MLTIB was measured. The relative risk ratios of the MRI findings and intraoperative bleeding were measured. Receiver operating characteristic (ROC) analysis was used to evaluate the ability of the MLTIB to help predict intraoperative haemorrhage in pregnant women with PAS.

RESULTS

Of the 86 pregnant women, 32 had intraoperative blood loss ≥ 1000 ml; of these, 18 had intraoperative blood loss ≥ 2000 ml. Abnormal vascularization of placental bed was associated with the highest relative risk ratio for the detection of intraoperative haemorrhage (RR = 10.66), followed by the presence of T2-dark intraplacental bands (RR = 8.02). The optimal cut-off of the MLTIB for predicting intraoperative haemorrhage (≥ 1000 ml) in pregnant women with PAS was 28.95 mm, and the AUC was 0.91 (sensitivity: 84%; specificity: 91%). The optimal cut-off of the MLTIB for predicting massive intraoperative haemorrhage (≥ 2000 ml) was 35.65 mm, and the AUC was 0.94 (sensitivity: 89%; specificity: 85%).

CONCLUSION

MLTIB was related to intraoperative haemorrhage in pregnant women with PAS. An MLTIB greater than 28.95 mm is an effective predictor of intraoperative haemorrhage. An MLTIB of 35.65 mm or greater strongly suggests the possibility of massive intraoperative haemorrhage.

Clinical analysis of second-trimester pregnancy termination after previous caesarean delivery in 51 patients with placenta previa and placenta accreta spectrum: a retrospective study

BACKGROUNDS

Pregnancy termination during the second trimester in patients with placenta previa and placenta accreta spectrum (PAS) is a complex and challenging clinical problem. Based on our literature review, there has been a relative increase in the number of such cases being treated by hysterotomy and/or local uterine lesion resection and repair. In the present study, a retrospective analysis was conducted to compare the clinical outcomes when different management strategies were used to terminate pregnancy in the patients with placenta previa and PAS.

METHODS

A total of 51 patients who underwent pregnancy termination in the second trimester in Beijing Obstetrics and Gynecology Hospital between June 2013 and December 2018 were retrospectively analyzed in this study. All patients having previous caesarean delivery (CD) were diagnosed with placenta previa status and PAS.

RESULTS

① Among the 51 patients, 16 cases received mifepristone and misoprostol medical termination, 15 cases received mifepristone and Rivanol medical termination, but 1 of them was transferred to hysterotomy due to failed labor induction, another 20 cases were performed planned hysterotomy. There was no placenta percreta cases and uterine artery embolization (UAE) was all performed before surgery.② There were 31 cases who underwent medical termination and 30 cases were vaginal delivery. Dilation and evacuation (D&E) were used in 20 cases of medical abortion failure and in all 30 cases of difficult manual removal of placental tissue. ③ A statistically significant difference was found among the three different strategies in terms of gestational weeks, the type of placenta previa status, main operative success rate and β-HCG regression time (P < 0.05). ④ There were 4(7.8%) cases who were taken up for hysterectomy because of life-threatening bleeding or severe bacteremia during or after delivery and hysterotomy. The uterus was preserved with the implanted placenta partly or completely left in situ in 47(92.2%) cases. Combined medical and/or surgical management were used for the residual placenta and the time of menstrual recovery was 52(range: 33 to 86) days after pregnancy termination.

CONCLUSIONS

Terminating a pregnancy by vaginal delivery through medical induction of labor may be feasible if clinicians have an overall understanding of gestational age, the type of placenta previa status, the type of placenta accreta, and patients concerns about preserving fertility. A collaborative team effort in tertiary medical centers with a very experience MDT and combined application of multiple methods is required to optimize patient outcomes.

Placental adhesion disorder: magnetic resonance imaging features and a proposal for a structured report

Placental adhesion disorder encompasses the various types of abnormal placentation that occur when the chorionic villi penetrate the uterine wall. Placenta accreta has become more common, mainly because of the increasing rates of cesarean section. Although ultrasound is the first-line imaging modality for evaluation of the placenta, it plays a limited role in cases of posterior placenta accreta and inconclusive findings. In such cases, magnetic resonance imaging (MRI) is indicated, mainly because it is a more accurate means of identifying placental invasion of extrauterine structures in high-risk pregnant women. In this review article, we present the ten major and minor MRI features of placental adhesion disorder, as described in the international literature. In addition, we propose a template for structured reports of MRI examinations of the placenta. We have also devised a guided questionnaire in order to identify risk factors in patients scheduled to undergo such examinations, with the objective of facilitating the multidisciplinary treatment planning needed in order to minimize maternal morbidity and mortality.

Management of patients with placenta accreta spectrum disorders who underwent pregnancy terminations in the second trimester: A retrospective study

PURPOSE

To analyse the management of patients with placenta accreta spectrum (PAS) disorders who underwent 2^nd trimester pregnancy terminations.

METHOD

The records of patients with PAS disorders who underwent 2^nd trimester pregnancy terminations were collected and analysed.

RESULTS

Twenty-eight patients were included; 8 (28.6%) patients received prenatal diagnoses and 20 (71.4%) patients received postnatal diagnoses. In the prenatal diagnosis group, scheduling hysterotomy and placenta removal were performed in 5 patients with complete placenta previa and previous caesarean delivery without hysterectomy or postpartum haemorrhage, and medical termination was performed in 3 patients, 2 of whom retained the placenta in situ. In the postnatal diagnosis group, the placenta remained in situ in 11 patients, and in 13 (46.4%) patients overall, adjuvant treatments were applied to the patients, and the abnormally implanted placenta was passed 43.5 (range: 7-102) days after termination. A complication associated with the placenta left in situ included intrauterine infection in one case. Uterus preservation was achieved in all the patients.

CONCLUSIONS

For patients with PAS disorders with complete placenta previa and previous caesarean delivery, hysterotomy is a safe choice for terminating a 2^nd trimester pregnancy. When it is impossible to manually remove the placenta, leaving the placenta in situ with the administration of adjuvant treatment is a good choice for uterus preservation.

Risk scoring system with MRI for intraoperative massive hemorrhage in placenta previa and accreta

BACKGROUND

Placenta previa and accreta are serious obstetric conditions that are associated with a high risk of intraoperative massive hemorrhage.

PURPOSE

To develop a scoring system for intraoperative massive hemorrhage combining MRI and clinical characteristics to predict the risk of massive hemorrhage in placenta previa and accreta STUDY TYPE: Retrospective cohort study.

SUBJECTS

In all, 374 patients consisting of 259 patients with placenta previa and accreta after previous cesarean section (CS) for the derivation cohort and 115 patients for the validation cohort.

FIELD STRENGTH/SEQUENCE

1.5T single-shot fast spin-echo sequence. [Correction added on October 23, 2019, after first online publication: The field strength in the preceding sentence was corrected.] ASSESSMENT: Using the derivation cohort, clinical and MRI data were collected and multivariable logistic regressions analysis was conducted to develop a scoring system for prediction of intraoperative massive bleeding (blood loss volume > 2000 mL). Finally, the scoring system was validated on 115 patients.

STATISTICAL TESTS

Student's t-test, Mann-Whitney U-test, X ² statistics, multivariable analysis, and receiver operating characteristic (ROC) analysis.

RESULTS

Ten indicators, including clinically maternal age (1 point), preoperative hemoglobin level (1 point), gravidity number (1 point), number of CS (1 point), and MRI T₂ dark intraplacental bands (4 points), cervical canal length (3 points), placenta thickness on the uterine scar area (4 points), empty vascular shadow of the uterus (1 point), low signal discontinuity in the muscular layer of the posterior wall of the bladder (6 points) and attachment position of the placenta (1 point) were imputed. From the ROC analysis, a total score of 7 points was identified as the optimal cutoff value, allowing good differentiation of intraoperative massive bleeding in the derivation cohort (AUC, 0.863; 95% confidence interval [CI]: 0.811-0.916) and in the validation cohort (AUC, 0.933; 95% CI: 0.885-0.980).

DATA CONCLUSION

The scoring system for intraoperative massive hemorrhage consists of MRI and clinical indicators, and using a cutoff value of 7 points for a high risk of massive bleeding, the developed scoring system could accurately assess the risk of intraoperative massive hemorrhage in patients with placenta previa and accreta. This scoring system can potentially reduce the incidence of intraoperative massive bleeding by identifying patients at high risk.

LEVEL OF EVIDENCE

3 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2020;51:947-958.

Pre-clinical magnetic resonance imaging of retroplacental clear space throughout gestation

INTRODUCTION

Visualization of the retroplacental clear space (RPCS) may provide critical insight into the development of abnormally invasive placenta (AIP). In this pre-clinical study, we characterized the appearance of the RPCS on magnetic resonance imaging (MRI) during the second half of gestation using a liposomal gadolinium contrast agent (liposomal-Gd).

MATERIALS AND METHODS

Studies were performed in fifteen pregnant C57BL/6 mice at 10, 12, 14, 16, and 18 days of gestation. MRI was performed on a 1T permanent magnet scanner. Pre-contrast and post-contrast images were acquired using T1-weighted gradient-recalled echo (T1w-GRE) and T2-weighted fast spin echo (T2w-FSE) sequences. Animals were euthanized after imaging and feto-placental units harvested for histological examination. Visualization of the RPCS was scored by a maternal-fetal radiologist and quantified by measuring the contrast-to-noise ratio (CNR) on T1w images. Feto-placental features were segmented for analysis of volumetric changes during gestation.

RESULTS

Contrast-enhanced T1w images enabled the visualization of structural changes in placental development between days 10-18 of gestation. Although the placental margin on the fetal side was clearly visible at all time points, the RPCS was partially visible at day 10 of gestation, and clearly visible by day 12. Hematoxylin and eosin (H&E) staining of the placental tissue corroborated MRI findings of structural and morphological changes in the placenta.

CONCLUSIONS

Contrast-enhanced MR imaging using liposomal-Gd enabled adequate visualization of the retroplacental clear space starting at day 12 of gestation. The agent also enabled characterization of placental structure and morphological changes through gestation.

Use of Postpartum Magnetic Resonance Imaging for Diagnosis and Classification of Retained Placenta Tissue

OBJECTIVE

To study the potential application of magnetic resonance imaging (MRI) for classification of retained placental tissue (RPT) in the uterus postnatally.

METHODS

Twenty-two patients with clinically or pathologically proven RPT were studied.

RESULTS

The thickness ratio (D1/D2) of invaded (D1) to normal (D2) myometrium could be categorized into 3 groups (>0.6, 0.1-0.6, and <0.1) correlating with the 3 types of RPT: accreta vera (RPA), increta (RPI), and percreta (RPP) (r = -0.861, P < 0.01). After uterine arterial embolization, the RPT showed lower signal intensity than the myometrium without flow voids on T2-weighted images. Two cases of RPP showed gradual enhancement, except 1 case of infection and 2 cases that did not involve enhancement examinations, whereas 17 cases of RPA and RPI showed early enhancement.

CONCLUSIONS

Magnetic resonance imaging can facilitate diagnosis of RPT severity. Dynamic contrast enhancement can indicate RPT activity and blood supply, thereby ensuring appropriate clinical decision making.

Management strategies for patients with placenta accreta spectrum disorders who underwent pregnancy termination in the second trimester: a retrospective study

Background

The unique clinical features of pregnancy termination in the second trimester with concurrent placenta accreta spectrum (PAS) disorders place obstetricians in a complex and delicate situation. However, there are limited data on this rare and dangerous condition. The objective of this research was to investigate and evaluate the clinical management strategies of this patient group.

Methods

The medical records of patients who were diagnosed and treated in our hospital from December 2005 and December 2015 were retrospectively reviewed.

Results

A total of 29 patients were included in this analysis. A prenatal diagnosis was suspected in 8 (27.6%) patients, and the remaining 21 (72.4%) patients were diagnosed after pregnancy termination in the second trimester. In the subgroup with a prenatal diagnosis, a planned hysterotomy was performed in 7 patients who had total placenta previa and previous cesarean delivery. The remaining patient received medical termination. A subtotal hysterectomy was performed in 3 (10.3%) patients for life-threatening bleeding during hysterotomy, and the uterus was preserved with an in situ placenta in the remaining 5 patients. In the subgroup with a postnatal diagnosis, the implanted placenta remained partly or completely in situ in all 21 patients under informed consent. Ultimately, the implanted placenta remained partly or completely in situ in 26 (89.7%) patients in the two subgroups. With the application of adjuvant treatments, including uterine artery embolization and medication followed by curettage under ultrasound guidance, the implanted placenta was passed 76.6 (range: 19 to 192) days after termination. Uterus preservation was achieved in all 26 patients. The complications associated with conservative management included delayed postnatal hemorrhaging (2 cases, 7.7%), fever (6 cases, 23.1%), G1 transaminase disorder (4 cases, 15.4%), and myelosuppression (1 case, 3.8%). Seven women (26.9%) had a spontaneous pregnancy after conservative management, and no patient experienced recurrent PAS disorders.

Conclusions

Leaving the implanted placenta in situ is the preferred choice for patients with PAS disorders who underwent pregnancy termination in the second trimester and desired fertility preservation. Multiple adjuvant treatment modalities, either alone or in combination, may help to promote the passing or absorption of the implanted placenta under close monitoring.

Scoring model to predict massive post-partum bleeding in pregnancies with placenta previa: A retrospective cohort study

AIM

We aimed to identify factors associated with massive post-partum bleeding in pregnancies with placenta previa and to establish a scoring model to predict post-partum severe bleeding.

METHODS

A retrospective cohort study was performed in 506 healthy singleton pregnancies with placenta previa from 2006 to 2016. Cases with intraoperative blood loss (≥2000 mL), packed red blood cells transfusion (≥4), uterine artery embolization, or hysterectomy were defined as massive bleeding. After performing multivariable analysis, using the adjusted odds ratios (aOR), we formulated a scoring model.

RESULTS

Seventy-three women experienced massive post-partum bleeding (14.4%). After multivariable analysis, seven variables were associated with massive bleeding: maternal old age (≥35 years; aOR 1.79, 95% confidence interval [CI] 1.00-3.20, P = 0.049), antepartum bleeding (aOR 4.76, 95%CI 2.01-11.02, P < 0.001), non-cephalic presentation (aOR 3.41, 95%CI 1.40-8.30, P = 0.007), complete placenta previa (aOR 1.93, 95%CI 1.05-3.54, P = 0.034), anterior placenta (aOR 2.74, 95%CI 1.54-4.89, P = 0.001), multiple lacunae (≥4; aOR 2.77, 95%CI 1.54-4.99, P = 0.001), and uteroplacental hypervascularity (aOR 4.51, 95%CI 2.30-8.83, P < 0.001). We formulated a scoring model including maternal old age (<35: 0, ≥35: 1), antepartum bleeding (no: 0, yes: 2), fetal non-cephalic presentation (no: 0, yes: 2), placenta previa type (incomplete: 0, complete: 1), placenta location (posterior: 0, anterior: 1), uteroplacental hypervascularity (no: 0, yes: 2), and multiple lacunae (no: 0, yes: 1) to predict post-partum massive bleeding. According to our scoring model, a score of 5/10 had a sensitivity of 81% and a specificity of 77% for predicting massive post-partum bleeding. The area under the receiver-operator curve was 0.856 (P < 0.001). The negative predictive value was 95.9%.

CONCLUSION

Our scoring model might provide useful information for prediction of massive post-partum bleeding in pregnancies with placenta previa.

Diagnosis of abnormally invasive posterior placentation: the role of MR imaging

Abnormally invasive placentation is becoming more common with a recent increase in cesarean sections and maternal age, among other risk factors. Ultrasonography is the first line-imaging, but it can be difficult to diagnose when limiting factors are present. Failure to recognize this serious placental abnormality precludes us from making the appropriate plan for the delivery and consequently can lead to fatal results. In this report, we present a case in which magnetic resonance imaging was used to diagnose posterior placenta increta missed by multiple sonographic examinations in a patient with previous myomectomies, and we also include a review of the literature on this topic. It is our conclusion that magnetic resonance imaging is superior to sonography to diagnose abnormally invasive placentation in cases of posterior placenta previa and high pretesting probability.

Prophylactic abdominal aorta balloon occlusion during caesarean section: a retrospective case series

BACKGROUND

The management of patients with morbidly adherent placenta has been described using vascular balloon catheters placed in the iliac arteries, but rarely in the aorta. This case series presents our experience with prophylactic lower abdominal aorta balloon occlusion in 45 women.

METHODS

The records of patients in our centre who underwent caesarean section between May 2013 and June 2014 were retrospectively analysed for the use of prophylactic lower abdominal aorta balloon occlusion.

RESULTS

Forty-five cases were identified. All patients had a morbidly adherent placenta, including placenta accreta (n=22), placenta increta (n=20) and placenta percreta (n=3). A subtotal hysterectomy was performed in four cases. Eleven of the 45 patients received red blood cell transfusion of a mean of 1.7 units. Mean preoperative and postoperative haemoglobin concentrations were 10.1g/dL and 9.4g/dL, respectively. Mean estimated blood loss was 835mL [range 200-6000mL]. The incidence of complications was 4.4% (2/45), including one case of lower extremity arterial thrombosis and one case of ischaemic injury to the femoral nerve. Follow up at one year was completed in 22 patients at which time all babies were well.

CONCLUSIONS

Prophylactic lower abdominal aorta balloon occlusion has the potential to reduce intraoperative blood loss, transfusion and hysterectomy rate in patients with morbidly adherent placenta undergoing caesarean section. Careful patient selection is critical as the technique may be associated with potentially serious complications.