What is the risk of pregnancy loss after amniocentesis as per Royal College of Obstetricians and Gynaecologists (RCOG) and International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) guidelines?

Risk of Pregnancy Loss After Amniocentesis According to RCOG and ISUOG Guidelines

According to current guidelines, the procedure-related miscarriage risk for genetic amniocentesis is approximately 0.25%-0.50% (1/400-1/200). 1

Procedure-Related Risks

The risk of pregnancy loss after amniocentesis varies based on several factors:

• Standard mid-trimester amniocentesis (15-18 weeks): 0.25%-0.50% (1/400-1/200) 1
• This is lower than the risk associated with chorionic villus sampling (CVS), which is approximately 0.5%-1.0% (1/200-1/100) 2, 1
• The background risk of spontaneous pregnancy loss in the second trimester is approximately 2-3% 1

A recent systematic review and meta-analysis from 2019 suggests that the procedure-related risk may be even lower than traditionally quoted:

• When comparing amniocentesis to control groups with similar risk profiles, the procedure-related risk was found to be only about 0.12% 3

Risk Factors for Increased Pregnancy Loss

Several factors have been identified that may increase the risk of fetal loss following amniocentesis:

• Maternal factors:

  • Advanced maternal age (OR: 2.0) 4
  • History of vaginal spotting (OR: 2.2) or serious bleeding (OR: 3.5) during pregnancy 4
  • History of multiple spontaneous abortions (OR: 3.0) or surgical abortions (OR: 2.1) 4
  • Presence of uterine fibromas (OR: 3.0) 4

• Procedure-related factors:

  • Stained amniotic fluid (OR: 6.1) 4
  • Operator experience (varies by center and practitioner) 1

Special Considerations for Twin Pregnancies

Twin pregnancies have specific considerations:

• The attributable risk of pregnancy loss before 24 weeks' gestation after mid-trimester amniocentesis in twin pregnancies is approximately 1.8% (1 in 56) 5
• More recent data from 2022 suggests lower rates with modern techniques, with pregnancy loss rates within 4 weeks after the procedure at 1.9% 6
• Twin pregnancies with abnormal ultrasound findings had a significantly higher rate of pregnancy loss (relative risk 4.81) 6

Timing Considerations

• Genetic amniocentesis is typically performed between 15-18 weeks' gestation 1
• Early amniocentesis (11-14 weeks) is considered investigational and may carry higher risks 1
• Late amniocentesis (after 24 weeks) has higher technical difficulty and potential complication rates 1

Other Potential Complications

• Infection (chorioamnionitis) occurs rarely (<0.1%) after amniocentesis 1
• Unlike CVS, amniocentesis is not associated with an increased risk of limb deficiency 2

Clinical Implications

• The timing of obtaining results from amniocentesis is relevant because of the increased risks for maternal morbidity and mortality associated with terminating pregnancy during the second trimester compared with the first trimester 2
• Earlier diagnosis through genetic amniocentesis has a psychological advantage before fetal movement is strongly felt 1

The procedure-related risk of miscarriage after amniocentesis should be discussed during pre-procedure counseling, along with the benefits of genetic diagnosis, to allow patients to make informed decisions about undergoing the procedure.