Objective
We sought to describe the potential value of 11-14 weeks’ screening for placenta accreta (PA).
Study Design
Patients with a history of lower segment cesarean section were prospectively included between 11-13+6 weeks over a 1.5-year period. The first 258 were offered standard screening whereas the following 105 underwent screening for PA. Women were considered high-risk when the trophoblast overlapped the scar visualized by transvaginal ultrasound and low-risk otherwise.
Results
The group screened for PA did not differ from the nonscreened group for demographic characteristics. In all, 6 of 105 (5.8%) women were considered high-risk. In the nonscreened group, 1 case of PA was discovered during an elective repeat cesarean. In the screened population, 1 case of PA occurred in a high-risk patient allowing a conservative planned management at 35 weeks.
Conclusion
At 11-14 weeks, ultrasound may help risk stratification for PA with a specific follow-up. Early recognition of patients at risk might improve the perinatal outcome of PA.
Placenta accreta (PA) is a life-threatening obstetrical condition that occurs when a defect of the decidua basalis enables the direct apposition of chorionic villi to the myometrium. As a result, at least part of the placenta cannot separate after delivery and this may lead to severe obstetric hemorrhage. It has become the principal indication for postpartum hysterectomy as well as for related surgical injuries. The incidence of PA has increased 4-fold from 1994 through 2002, following the increase in cesarean delivery rates over the same period of time. Most PA present as placenta previa in the third trimester with an incidence of 9.3% in this group compared with 0.005% when the placenta is normally inserted. Among women with placenta previa, maternal age ≥35 years and previous cesarean delivery are independent risk factors, with an incidence of 2% for women aged <35 years and no cesarean section up to 38% in women aged ≥35 years and ≥2 previous cesarean sections.
It is important to diagnose PA prior to delivery, to allow for optimal concerted management planning and prevention of severe maternal morbidity and mortality. The diagnosis of PA by ultrasound and magnetic resonance imaging (MRI) in the second and third trimester of pregnancy remains largely speculative, even in high prevalence cohorts, and most cases are only diagnosed at the time of delivery in cases with prepartum or postpartum hemorrhage. The timing of the defective trophoblast implantation leading to PA suggests that this condition could be identified during the 11-14 weeks’ ultrasound.
Signs of PA have been recognized as early as the first trimester in several case reports. However, these findings have never been implemented in a prospective early screening strategy. The main aim of our study was to describe the potential use of routine 11-14 weeks’ scan for screening for PA in women with a history of delivery by lower segment cesarean section (LSCS).
Materials and Methods
The screening procedure for PA was defined in patients with a history of LSCS as follows: a transvaginal midsagittal plane was defined, including the cervical canal, the bladder, and the lower part of the gestational sac. Both the uterine scar and the location of the trophoblast were recognized and located. The relationship between the uterine scar and the trophoblast thus defined the high-risk group. A patient was considered high-risk when the scar was exposed within the uterine cavity above the lowest part of the gestational sac, which encompasses the cervix and part of the inferior segment together with a covering low-lying placenta ( Figure 1 ) . A patient was considered low-risk either when the uterine scar was protected within the cervicoisthmic canal ( Figure 2 , A) or when the trophoblast was not covering the internal os ( Figure 2 , B).
The population considered for this study comprises all consecutive cases of patients with a history of lower segment uterine scar over a 1.5-year period (September 2008 through March 2010) attending our unit for first-trimester screening at 11-13+6 weeks as defined by a crown-rump length between 45-84 mm. During a first period of time, patients were not specifically screened for placenta and scar location. In a second period, patients were screened for PA by transvaginal ultrasound.
All ultrasounds were performed using a General Electrics Voluson E8 or 730 Expert (GE Medical System Europe, Buc, France) with a 3.5- to 5-MHz or 6- to 8-MHz transvaginal transducer.
Demographic data as well as obstetrical and perinatal management and outcome were prospectively recorded in our electronic database (Astraia, Munich, Germany). Patients considered high-risk were followed up prospectively with serial ultrasound focusing on ultrasound signs of placental invasion in our unit up until delivery.
The statistical analysis was conducted using R ( www.r-project.org ). Quantitative variables are summarized by the median and interquartile range (25th-75th centile) and qualitative variables are described by N (%). Comparisons of demographic characteristics between the screened and nonscreened populations were performed using Mann-Whitney U tests for quantitative variables and Fisher exact tests for qualitative variables.
Since transvaginal ultrasound is offered routinely for first-trimester screening in our practice, this study did not require an institutional review board; however, written informed consent was obtained from all women.
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