A case of a cervico-isthmic pregnancy without abnormal location of placenta

Introduction

Cervico-isthmic pregnancy (CIP) is diagnosed when the gestational sac (GS) implants between the uterine cervix and isthmus. CIP is often complicated by placenta previa and placental adhesion [1] and can result in life-threatening bleeding during pregnancy or delivery [2–6]. On the other hand, we present a case of CIP without abnormal location of placenta and raised another clinical problem.

Case

A pregnant 39-year-old Japanese woman (gravid 3/para 2) presented with vaginal bleeding at 6 weeks’ gestation. Her last pregnancy resulted in missed abortion, and uterine curettage was performed. Other medical history was unremarkable. On transvaginal ultrasonography (TVS), the GS was located near the uterine cervix, and she was diagnosed with an inevitable abortion. A week later, an embryo with cardiac activity was noted, and she was referred on suspicion of a cervical pregnancy. TVS at 8 weeks’ gestation showed a fetus in the GS near the uterine cervix, and the endometrial line from the GS to uterine fundus was identified (Figure 1). On speculum examination, the cervix appeared normal, with no evidence of cervical pregnancy, and the patient was diagnosed with CIP. After being informed of the risks associated with CIP, she elected to continue the pregnancy. At 14 weeks, the uterine cavity was occupied, and the characteristic ultrasonographic findings became unclear. The cervical length was 23 mm, and there was no placenta previa. At 17 weeks, the cervical length shortened to 13 mm. At 21 weeks, fetal growth was good, the fetal membrane was visible, but the cervix was dilated to 3 cm without uterine contractions. Cervical incompetency was diagnosed, and an emergency cervical cerclage (McDonald operation) was conducted. At 28 weeks, suspicious ultrasonographic findings of placenta accreta, including significant myometrial thinning, loss of the retroplacental clear zone, and the presence of placental lacunae, were noted. Magnetic resonance imaging at 29 weeks confirmed that the placenta was located on the posterior wall of the uterus and that the length between the internal os and placental margin was 6 cm. Myometrial thinning was apparent, but the left uterine fundal portion was less affected (Figure 2). On imaging, placental location seemed normal, but the thickened myometrium was thought to represent the uterine fundus, and the thinning region, the excessive stretching of the isthmus caused by placental implantation. During the course of the pregnancy, the patient did not experience further vaginal bleeding. To mitigate any surgical bleeding, 1600 mL of autologous blood was collected during the pregnancy.

Figure 1

Ultrasonographic findings at 8 weeks’ gestation. The GS was located near the uterine cervix, and a fetal heartbeat was noted. The endometrial line ran from the GS to uterine fundus, and the uterine cavity was empty. The cervical length was preserved. Cx=uterine cervix, F=fetus, GS=gestational sac, Em=endometrial line.

Figure 2

MRI images at 29 weeks’ gestation. In the sagittal view, (A) the placenta is located on the posterior wall and far from the internal os. (B) While the myometrium was generally thin, the uterine cranial part remained thick, indicating that the uterine corpus was not as expanded. MRI=magnetic resonance imaging, Cx=uterine cervix, PI M=Placental margin, C=uterine corpus.

In the counseling for her operation, we proposed the choice to retain her uterus as our previous case [7]. However, the patient and her family did not plan future pregnancies, so a cesarean hysterectomy using bilateral common iliac artery balloon catheters was performed at 37 weeks. During laparotomy, a vesicouterine fold of the visceral peritoneum extended toward the cranial region. To prevent resection of the placenta during surgery, after confirming the placental location, a transverse incision of the lower part of the uterus was performed. A female infant weighing 2600 g, with Apgar scores of 6 and 8 at 1 and 5 min, respectively, was successfully delivered. The umbilical artery pH was 7.313. The placenta did not spontaneously detach after delivery, and to avoid massive hemorrhage, manual removal was not attempted. During the hysterectomy, the bilateral common iliac artery balloons were expanded immediately prior to excision of the cardinal ligament. During surgery, blood flow was interrupted for 20 min, and total blood loss was 2200 mL (including amniotic fluid). The patient was transfused with 1600 mL of autologous blood. The mother and child were in good general condition and were discharged on postoperative day 6.

Histological examination revealed a barrel-shaped uterus; the myometrium of the uterine corpus seemed thickened, and the cervix was significantly effaced (Figure 3). The placenta was located in the upper cervix and was difficult to exfoliate manually. The placental tissue was close to the uterine cervical tissue and extended into the myometrium, indicating placenta increta.

Figure 3

Macroscopic features of excised uterus. (A) The uterus was barrel-shaped; the myometrium of uterine corpus seemed thickened, and the cervix (Cx) was significantly effaced. (B) Histological examination revealed placental tissue penetrating into the myometrium, and the diagnosis of placenta increta was confirmed (arrows). Cx=uterine cervix, C=uterine corpus.

Discussion

An ultrasonographic diagnosis of CIP is made when the GS is located between the uterine cervix and corpus with an empty uterine cavity above the GS [6, 8]. For differentiation between CIP and a true cervical pregnancy, Strobelt et al. [6] reported that, on TVS during the first trimester, the GS is located more cranially in CIP and is found between the cervix and the decidualized functional endometrium. In this case, CIP was diagnosed based on the findings that the GS was located between the cervix and the uterine corpus, and the cervical length was preserved at 8 weeks’ gestation. However, from 14 weeks’ gestation, occupation of the uterine cavity and normal placement of the placenta made the diagnosis of CIP uncertain. Twelve cases of CIP without placenta previa have been reported [3, 4, 6, 8–14]. In seven of these, a diagnosis of CIP was made during or after delivery because of massive bleeding followed by the need for hysterectomy (Table 1). This suggests that CIP without placenta previa did not show significant ultrasonographic findings after the second trimester. Early ultrasonographic diagnosis during the first trimester is essential to explain the risks of continuing a CIP to the patient and to prepare for life-threatening massive bleeding during pregnancy and delivery.

In this case, a cervical incompetency was detected at 20 weeks’ gestation. There are few reports that focused on an association between a CIP and cervical incompetency. In five of 12 cases, cervical dilatation was noted during pregnancy, and in five cases, shortened cervical length was noted (Table 1). Cervical dilatation was more frequently encountered in multiparous patients than in primiparous patients, who mostly presented with a shortened cervix alone. Honda et al. [3] suggested monitoring of the cervical length to prevent preterm delivery because an enlarged GS in the uterine isthmus can cause cervical effacement and dilatation. We agree with their suggestion. In a CIP without placenta previa, because of excessive stretching of the isthmus, the internal os cannot remain closed after the second trimester, and evaluation of cervical length and dilatation is needed during the early second trimester. Further, cervical cerclage should be considered to avoid premature membrane rupture and/or preterm delivery.

In conclusion, CIP diagnosis during early gestation is essential. It is because CIP without placenta previa does not show any significant ultrasonographic findings, and the diagnostic delay will lead to maternal complications, such as massive bleeding and/or hysterectomy at delivery. Further, careful evaluation of cervical length and dilatation during the early second trimester could detect complications such as cervical incompetency.