SUMMARY:

Implantation of a pregnancy within the scar or uterine defect from a prior cesarean delivery is called a Cesarean Scar Pregnancy (CSP).  CSP is a complication of early pregnancy and carries significant risks of severe maternal morbidity. It should not be expectantly managed. However, optimal treatment between surgical, medical, or minimally invasive therapies are currently unknown.  Patients who choose expectant management, although not recommended, should be delivered between 34w7d and 35w6d by repeat cesarean with strong counseling regarding subsequent risks for repeat CSP

BACKGROUND:

• Occurs when the blastocyst implants in the scar from prior cesarean delivery, hypothesized to be microscopic dehiscence of scar tract
• Implantation occurs within the uterine cavity and can therefore result in live infant, unlike true ectopic pregnancies outside the uterus
• Incidence
  • Increasing incidence due to increased rates of cesarean delivery and improved imaging to detect CSP

Typical Clinical Presentations

• Average gestational age at presentation: 7.5 weeks
  • Estimated incidence 1:1800 to 1:2656
• Variable clinical presentation
  • Typically presents in first trimester | Rarely second trimester
  • Asymptomatic: 33%
  • Painless vaginal bleeding: 33%
  • Uterine rupture and hemoperitoneum: Rare
• Two types of implantation patterns for CSP
  • Endogenic (“on the scar”): Variable outcomes due to growing towards the uterine cavity
  • Exogenic (“in the niche”): Most often results in placenta accreta spectrum requiring hysterectomy

Risk Factors

• Prior cesarean delivery
  • Unclear if multiple prior cesarean sections increase risks of CSP
  • Approximately 50% of patients may have only a single prior cesarean delivery
• Prior cesarean section for breech presentation may be a risk factor
  • Malpresentation may result in less developed lower uterine segment | Thicker hysterotomy has greater risk for poor healing | Higher risk for subsequent microscopic dehiscence
  • No data to link CSP and prior hysterotomy closure technique

DIAGNOSIS:

Ultrasound

• Primary imaging modality
• Transvaginal ultrasound has highest resolution and is considered the optimal modality
  • Findings of low anterior gestational sac should raise diagnostic suspicion for CSP
  • Recommend high degree of suspicion given morbidity of delayed diagnosis
• Proposed ultrasonographic criteria (Not all are required)
  • Empty uterine cavity and empty endocervix
  • Embedded placenta or gestational sac seen within hysterotomy scar
  • Gestational sac that fills shallow area representing healed hysterotomy site (the “niche”) | <8 weeks gestation has triangular sac | >8 weeks rounded or oval gestational sac
  • Myometrial layer between gestational sac and bladder is either thin (1 to 3mm) or completely absent
  • CSP with rich vascular pattern
  • Confirmation of pregnancy via embryonic or fetal pole or yolk sac (or both, with or without fetal cardiac activity)
• Other ultrasonographic findings
  • Lower uterine segment bulging in the midline on transabdominal view

Other Diagnostic Modalities

• 3D ultrasound and MRI
  • Benefit vs transvaginal ultrasound is unclear
• Laparoscopy
  • Has been used to confirm CSP with bulge at level of prior cesarean scar towards the bladder in an otherwise normal uterus

TREATMENT:

Optimal management for treatment of CSP is unknown

• Limited number of RCTs
• Balance between preserving maternal health and preserving fertility

Surgical Management of CSP

• SMFM suggests

…operative resection (with transvaginal or laparoscopic approaches when possible) or ultrasound-guided vacuum aspiration be considered for surgical management of CSP and that sharp curettage alone be avoided

• Sharp curettage alone not recommended due to high complication rates and requires additional treatment in approximately 50% of cases
  • Ultrasound-guided vacuum aspiration may be a superior alternative with lower complication rates and higher efficacy than curettage alone
• Consider gravid hysterectomy is those who do not desire future fertility

Medical Management and Adjunct Treatment

• SMFM suggests

…intragestational methotrexate for medical treatment of CSP, with or without other treatment modalities

We recommend that systemic methotrexate alone not be used to treat CSP

• Intragestational injection
  • 20-gauge needle
  • Transvaginal approach under ultrasound guidance
  • Sac aspiration prior to injection
  • Methotrexate: Comparable to ectopic pregnancy dosing | Consider 1mg/kg up to 50mg
  • KCl: Can also be used | Highly effective in heterotopic twin pregnancies
• Uterine artery embolization
  • In combination with other modalities may increase efficacy while decreasing complications, particularly bleeding
• Newer techniques: Tamponade of CSP using foley catheter
  • Double-balloon catheter (used for cervical ripening) prevents bleeding and terminates the CSP by compressing the gestational sac blood supply
  • SMFM considers this approach to “be well tolerated and efficacious, which supports a potential option that warrants further study”

Expectant Management of CSP

• Not recommended
• Counsel regarding risks:
  • Severe morbidity: Massive hemorrhage | Uterine rupture | PAS
  • Maternal death: Increased risk
  • Repeat cesarean delivery between 34w0d and 35w6d  

Note: Due to possibility of late preterm delivery and hemorrhage risk, administer betamethasone administration for fetal lung maturity and include a multi-disciplinary team with Level III/IV facility

Future Pregnancy Risks

• Subsequent pregnancies have an increased risk for recurrent CSP and consequent severe maternal morbidity and mortality
• Patient with subsequent pregnancies after CSP require
  • Close sonographic monitoring <8 weeks of gestation
  • Repeat cesarean section between 34w0d and 35w6d
  • Administer betamethasone as medically indicated
  • Massive hemorrhage precautions: Plan for delivery at a Level III/IV center with a multi-disciplinary team

KEY POINTS:

• High risk of complication in the second and third trimester with hysterectomy ranging from 50-100%
  • If unsure diagnosis: short follow up or second opinion or MRI should be considered
• Surgical management should include
  • Operative resection or ultrasound-guided vacuum aspiration
  • Avoid sharp curettage alone
• Medical treatment of CSP should include
  • Intragestational methotrexate with or without other treatment modalities
  • Avoid systemic methotrexate alone
• Expectant management of CSP is not recommended
  • If patient opts for this approach, manage similar to PAS with multi-disciplinary team and late preterm delivery
  • The only exception where expectant management can be considered is in the case of a non-viable pregnancy | However, expectant management is associated with a 20% increased risk for AV malformation following resolution and may take several months to resolve
• Risks of subsequent CSP should be discussed
  • Include discussion of LARC and other effective contraceptive methods
• Contribute data to the Cesarean Scar Pregnancy Registry (see ‘Learn More – Primary Sources’ below)

Learn More – Primary Sources:

SMFM Consult Series #49 – Cesarean Scar Pregnancy

Cesarean Scar Pregnancy Registry

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