What is the gestational age range that distinguishes second trimester uterine loss from intrauterine death?

Gestational Age Definitions: Second Trimester Loss vs Intrauterine Fetal Death

Second trimester uterine loss is defined as pregnancy loss occurring before 20 weeks of gestation, while intrauterine fetal death (IUFD) is defined as fetal death occurring at or after 20 weeks of gestation. 1, 2

Standard Gestational Age Thresholds

• The critical threshold distinguishing these two entities is 20 weeks (20 0/7 weeks) of gestation, which represents the internationally accepted definition for IUFD 1, 2, 3

• Pregnancy losses occurring before 20 weeks are classified as miscarriages or second trimester losses, not intrauterine fetal deaths 1

• The periviable period, which includes the transition zone, extends from 20 0/7 weeks to 25 6/7 weeks of gestation, where outcomes range from near-certain death to potential survival with significant morbidities 1

Clinical Context and Terminology

• First trimester losses occur before 14 weeks of gestation and are typically managed differently than second trimester losses 4

• Second trimester losses span from 14 weeks to just before 20 weeks (14 0/7 to 19 6/7 weeks) 1, 4

• IUFD or stillbirth begins at 20 0/7 weeks and continues through term pregnancy 2, 3

Management Implications of This Distinction

• The 20-week threshold has significant clinical implications, as uterine evacuation procedures for fetal demise at or after 20 weeks carry different risks compared to earlier gestational ages 4

• Gestational age of 20 weeks or greater is significantly associated with increased maternal morbidity during evacuation procedures (OR 2.59; 95% CI 1.39-4.84) 4

• Most fetal deaths in monoamniotic twin pregnancies occurring before 20 weeks are classified as spontaneous miscarriage rather than IUFD 1

Critical Considerations for Accurate Classification

• Accurate pregnancy dating is essential for proper classification, with first-trimester ultrasound crown-rump length (CRL) measurement being the gold standard for establishing gestational age 5, 6

• CRL measurement between 8-13 weeks provides accuracy within ±5-7 days, which is critical for determining whether a loss falls just before or after the 20-week threshold 5

• When a discrepancy of ≥5 days exists between last menstrual period and CRL dating in the first trimester, the CRL-based gestational age should be adopted for all clinical decision-making 5