First-Trimester Cesarean Scar
Pregnancy Evolving Into Placenta
Previa/Accreta at Term
Jara Ben Nagi, MD, Dede Ofili-Yebovi, MD, Mike Marsh, MD, Davor Jurkovic, MD
lacenta accreta is a rare but serious obstetric condition that is associated with considerable maternal morbidity and mortality.1A preoperative diag-nosis of placenta accreta is difficult, and it is usually established at cesarean delivery or on histologic examination after obstetric hysterectomy for post-partum hemorrhage. In women with placenta previa, an abnormally adherent pla-centa is suspected when there is an absent decidual interface between the plapla-centa and the myometrium. Another sign is the presence of unusually dilated vessels at the placental site.2,3Although the reported accuracy of sonographic diagnosis in the third trimester is reasonably high, late detection is of limited value because it does not prevent the serious complications of placenta accreta.
The first-trimester diagnosis of pregnancy implantation in a previous cesarean deliv-ery scar has been reported in recent years.4,5This condition is difficult to differentiate from cervical pregnancy, and it is likely that before the use of high-resolution transvagi-nal sonography, cesarean scar pregnancies were diagnosed and treated as cervical ectopic pregnancies. Cervical pregnancies rarely progress to term, whereas cesarean scar pregnancies may do so because of their position at the level of the internal os.
In 60% to 70% of cesarean scar pregnancies, there is clear evidence of trophoblast penetrating the endometrial-myometrial junction. It has been postulated that first-trimester cesarean scar pregnancies that invade the myometrium may develop into placenta previa/accreta if the pregnancy is allowed to progress.5In this report, we describe the case of a first-trimester cesarean scar pregnancy with evidence of myome-trial involvement that was managed expectantly and developed into placenta pre-via/accreta at term.
Received April 26, 2005, from the Early Pregnancy and Gynaecology Assessment Unit (J.B.N., D.O.-Y., D.J.) and Department of Obstetrics and Gynecology (M.M.), King’s College Hospital, London, England. Revision requested May 31, 2005. Revised manuscript accepted for publication June 16, 2005. Address correspondence to Davor Jurkovic, MD, Early Pregnancy and Gynecology Assessment Unit, King’s College Hospital, Denmark Hill, London SE5 8RX, England.
E-mail: davor.jurkovic@kcl.ac.uk
Case Report
A 37-year-old woman, gravida 6, para 3, with a history of vaginal bleeding at 5 weeks’ gestation was admitted for an early sonographic scan. The pregnancy was planned, and the size of the gestational sac corresponded to her certain menstrual dates. She had undergone 3 cesarean deliveries in the past. The first was an emergency cesare-an delivery at 40 weeks for fulminating preeclampsia. Subsequently, she had 2 elective cesarean deliveries at term, both of which were performed because of the
tory of previous emergency cesarean delivery. All of her children were living and healthy. She also had 2 first-trimester miscarriages before the cur-rent pregnancy that were treated by evacuation of the retained products of conception. Her gynecologic and medical histories were unre-markable.
First Trimester
A transvaginal scan performed at a gestational age of 5 weeks 5 days revealed a 3.7-mm gesta-tional sac. The sac was located at the level of the internal os. There was a wide gap in the anterior myometrium, which was covered only by a thin layer of echogenic tissue. The gestational sac was implanted into this gap, which was presumed to represent a deficient uterine cesarean delivery scar. In view of the small size of the sac and the history of vaginal bleeding, it was believed that there was a good chance that the pregnancy would miscarry. A decision was therefore made to continue with expectant management and to repeat the scan 1 week later.
The patient continued to have intermittent vaginal bleeding. At 6 weeks 3 days, she returned for another scan, which showed a viable embryo within the gestational sac. The sac was embed-ded deep within the myometrium and complete-ly filled the myometrial defect (Figure 1). In view of these findings, she was informed that the preg-nancy could develop into placenta previa/accre-ta and that she would be at risk of having major hemorrhaging that would require a hysterecto-my if the pregnancy were allowed to progress. After discussion, the patient decided to continue with the pregnancy and was asked to return 2 weeks later for another scan.
A follow-up sonographic scan was performed at 8 weeks 4 days, by which time the vaginal bleeding had stopped (Figure 2). On the sono-graphic scan, the embryo was developing nor-mally. The placenta was seen herniating through the left anterolateral aspect of the uterine wall toward the bladder and the left adnexa. Once again, she was counseled about the risks of seri-ous complications later in pregnancy, but she decided to continue with expectant manage-ment. An antenatal visit was arranged, and she was also scheduled for a routine nuchal translu-cency scan.
Second Trimester
The patient returned to the fetal medicine unit for a nuchal scan at 12 weeks 5 days. The fetus appeared normal, and the estimated risk of tri-somy 21 was 1:732. She was reassured by this result and decided against invasive testing for chromosomal abnormalities.
She returned at 14 weeks 5 days for shared hos-pital care. At admission, her blood pressure was 125/80 mm Hg, her hemoglobin level was 12.6 g/dL, and she had a positive test result for sick-le cell trait. Her blood group was A, RH D-posi-tive, and she had positive test results for anti-M antibodies. She was then seen at regular 4-week intervals by her community midwife. She remained asymptomatic and had a fetal
anoma-Figure 1.Sonographic image at 6 weeks’ gestation showing
Figure 2.Longitudinal section of the uterus showing the gesta-tional sac implanted in the anterior uterine wall. The trophoblast is herniating toward the left adnexa through the gap in the myometrium.
ly scan at 22 weeks 5 days, which showed no evi-dence of fetal structural defects; however, the placenta was noted to be low.
Third Trimester
The pregnancy continued without complica-tions, and she returned to our unit for another scan at 26 weeks. The scan revealed an anterior placenta previa with a thin, bulging, and defi-cient lower uterine segment (Figure 3). The decidual interface between the placenta and the myometrium was partially absent, and there were large dilated blood vessels in the same area. These sonographic features were suggestive of a placenta accreta.
She remained generally well, and 2 additional scans at 34 and 36 weeks confirmed the diagno-sis of placenta previa/accreta. A decision was made to admit her for an elective cesarean deliv-ery at 37 weeks 5 days. Her preoperative hemoglobin level was 10.3 g/dL. Four units of blood were cross-matched.
Cesarean Delivery
The operation was performed under general anesthesia. The entry into the peritoneal cavity was difficult because of the presence of scar tis-sue. The bladder was adherent to the lower uter-ine segment. The myometrium of the lower segment was severely deficient. The placenta protruded toward the left adnexa and was cov-ered with a thin layer of peritoneum. The
blad-der was dissected from the uterus, and the lower segment was incised. A healthy male neonate weighing 3.4 kg was delivered, with Apgar scores of 4 and 8 at 1 and 5 minutes, respectively. The placenta was firmly adherent to the myometri-um from which it could not be separated com-pletely (Figure 4). Severe hemorrhage ensued and could not be contained by uterotonics and conservative surgical measures; therefore, a decision was made to perform an emergency subtotal hysterectomy. The estimated blood loss was approximately 3500 mL, but the operation was otherwise uncomplicated. Two units of blood were transfused intraoperatively. Her post-operative hemoglobin level was 7.8 g/dL, but the recovery was otherwise uneventful. She was dis-charged to home 4 days later, and iron tablets were prescribed.
Histologic Findings
Macroscopic examination of the uterus showed that the lower uterine segment was dilated. On the left lateral side of the uterine wall, a 6 ×5-cm area of the myometrium measured only 0.3 cm in thickness and was covered by adherent blood. Microscopic analysis of the lower uterine seg-ment sections revealed the presence of interme-diate trophoblast and mature chorionic villi, which were extending deep into the myometri-um. No chorionic villi were found within the uterine cavity. The final histologic diagnosis was placenta increta.
Figure 3. Sonographic image at 26 weeks’ gestation revealing anterior placenta previa with large dilated blood vessels in the anterior uterine wall, which is suggestive of placenta accreta.
Figure 4. At the time of the cesarean delivery after the birth, the placenta remains firmly adherent to the myometrium, which is typical of placenta accreta.
Postnatal Visit
At a follow-up visit 6 weeks after the operation, the patient was well, and her abdominal incision was completely healed. She was advised to continue with routine smear tests in the future, and no fur-ther visits were arranged. She was asked for per-mission to present her case for publication to a scientific journal, and she gave her verbal consent.
Discussion
Our case shows that a successful diagnosis of placenta previa/accreta developing within a deficient cesarean delivery scar can be made during the first trimester of pregnancy. The crite-ria for a diagnosis of pregnancy implantation into uterine cesarean delivery scars have been described previously and include the visualiza-tion of a defect within the anterior uterine wall.6 The diagnosis of pregnancy implantation in a deficient scar is not difficult during the first few weeks of pregnancy because the gestational sac is very small, and the implantation site can be identified accurately. Furthermore, the lower segment is relatively thick, which facilitates the detection of a myometrial defect. At present, it is impossible to speculate whether a first-trimester diagnosis of placenta previa/accreta is more accurate and reproducible compared with a sec-ond-trimester diagnosis; however, it is interest-ing that in this case the diagnosis of abnormally adherent placenta was not suspected on trans-abdominal scans performed during the second trimester in our tertiary referral fetal medicine unit. It is unclear whether pregnancy implanta-tion over an apparently well-healed cesarean scar is also likely to result in placenta previa/acc-reta at term.
Most cases of first-trimester cesarean scar
preg-uterine scar. It has also been shown that abnor-mally adherent placentas account for 50% to 65% of all obstetric hysterectomies, 66% of which have a history of previous cesarean deliveries.12
The clinical importance of this complication is also illustrated by the most recent United Kingdom Confidential Enquiry into Maternal Deaths,13 which showed that 4 women died of placenta previa between 2000 and 2002. All of them had at least 1 previous cesarean delivery, with a histologic diagnosis of placenta accreta in 3 (75%) of 4 cases.
A first-trimester diagnosis of abnormal placen-tation gives women the option to choose between expectant management and termina-tion of pregnancy. Terminatermina-tion of pregnancy during the first trimester is complicated by sub-stantial hemorrhage in 20% to 40% of cases, but the risk of hysterectomy is low. The possibility of conserving the uterus is important to women who have not completed their families; however, should the woman opt for expectant manage-ment, antenatal care should be similar to that of other women with the diagnosis of major placen-ta previa. Early diagnosis helps ensure that senior medical staff are present at the time of delivery or miscarriage should an obstetric hysterectomy be required. This may not reduce the risk of hys-terectomy, but it is likely to decrease the chance of surgical complications and death.
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