What is the risk of miscarriage at 6 weeks of gestation?

Risk of Miscarriage at 6 Weeks of Gestation

The risk of miscarriage at 6 weeks of gestation is approximately 9.4% for asymptomatic women with confirmed fetal cardiac activity on ultrasound. 1

Risk Factors and Epidemiology

• The overall risk of miscarriage decreases significantly with advancing gestational age, from 9.4% at 6 completed weeks to 4.2% at 7 weeks, 1.5% at 8 weeks, 0.5% at 9 weeks, and 0.7% at 10 weeks. 1
• Worldwide, an estimated 23 million miscarriages occur annually, with a pooled risk of 15.3% among all recognized pregnancies. 2
• The population prevalence of women who have experienced one miscarriage is 10.8%, two miscarriages is 1.9%, and three or more miscarriages is 0.7%. 2

Risk Factors for Miscarriage

• Maternal age (younger than 20 years and older than 35 years) is a significant risk factor for miscarriage. 2
• Paternal age over 40 years increases miscarriage risk. 2
• Very low or very high body mass index (BMI) is associated with increased risk. 2
• Previous history of miscarriage significantly increases the risk of subsequent pregnancy loss. 2
• Lifestyle factors including smoking, alcohol consumption, stress, and working night shifts are associated with increased miscarriage risk. 2
• Environmental factors such as air pollution and pesticide exposure may contribute to pregnancy loss. 2

Predictive Factors for Pregnancy Continuation

• Embryonic/fetal heart rate (E/FHR) is the best single ultrasound predictor of pregnancy continuation, with a specificity and positive predictive value of 95.3% and 97.2%, respectively. 3
• An E/FHR greater than 113 beats per minute at 6 weeks is a strong predictor of pregnancy continuation. 3
• A combination of three ultrasound parameters (E/FHR >113 beats per minute, crown-rump length >19.9 mm, and gestational sac diameter >27.3 mm) has a specificity and positive predictive value of 98% and 99% for predicting pregnancy continuation. 3
• In pregnancies following assisted reproductive technology, maternal age, fetal heart activity, mean uterine artery pulsatility index, and serum glycodelin-A levels at 6 weeks can effectively identify pregnancies at risk of first-trimester miscarriage. 4

Consequences of Miscarriage

• Physical consequences include bleeding and infection. 2
• Psychological consequences include increased risk of anxiety, depression, post-traumatic stress disorder, and suicide. 2
• Miscarriage, especially recurrent miscarriage, is a sentinel risk marker for future obstetric complications including preterm birth, fetal growth restriction, placental abruption, and stillbirth. 2
• Pregnancy loss is also associated with longer-term health problems such as cardiovascular disease and venous thromboembolism. 2

Management Considerations

• For women experiencing threatened miscarriage, clinical parameters that could predict fetal viability include spotting/mild bleeding (versus heavy bleeding) and progesterone treatment. 3
• Progesterone levels are strongly predictive of miscarriage risk in women presenting with threatened miscarriage between 6-10 weeks gestation. 5
• The first trimester, particularly weeks 6-10, corresponds to the period of organogenesis and carries the highest risk for malformations if exposed to teratogens. 6
• Women without symptoms who have confirmed fetal cardiac activity at their first prenatal visit have a good prognosis, with over 98% chance of continuing beyond 20 weeks if presenting at 8 weeks or later. 1

Special Considerations

• Exposure to certain medications during early pregnancy may increase miscarriage risk, particularly during the period of organogenesis (6-10 weeks). 6
• Surgery during the first trimester carries a slightly higher risk of miscarriage and should be carefully considered. 6
• Diagnostic procedures such as chorionic villus sampling (CVS) carry a procedure-related miscarriage risk of approximately 0.5%-1.0%, while amniocentesis carries a risk of 0.25%-0.50%. 6

Understanding these risk factors and predictive indicators can help provide appropriate counseling and management for women in early pregnancy, particularly at the critical 6-week gestational age.