Uterine Lining Thickness in Blighted Ovum at 11 Weeks
In an 11-week pregnancy with a blighted ovum (anembryonic gestation), the decidualized endometrium (uterine lining) typically measures approximately 5-7 mm in total thickness, though this measurement is not routinely reported or clinically relevant in the context of pregnancy loss.
Understanding the Clinical Context
The question asks about "uterine lining thickness" in a pregnancy scenario, but this requires clarification of what is actually being measured:
In early pregnancy, the endometrium transforms into decidua, which forms the maternal component of the gestational sac and is not measured separately as "lining thickness" in the same way it would be in a non-pregnant state 1.
The gestational sac itself (11.1 mm in this case) is surrounded by decidualized tissue, but standard obstetric ultrasound protocols focus on the mean sac diameter, presence or absence of yolk sac and embryo, rather than measuring the decidual thickness 1.
What the Evidence Shows About Myometrial/Decidual Measurements
First Trimester Measurements
Myometrial thickness at 11 weeks gestation averages approximately 6-8 mm at various uterine sites (fundus, anterior wall, posterior wall), with the fundus typically measuring less than other sites 2.
Myometrial thickness is significantly greater in the first trimester compared to later trimesters, decreasing by approximately 35% from first to second trimester 2.
Lower Uterine Segment Specifically
At 11 weeks, the lower uterine segment measures approximately 6-7 mm in thickness in women without prior cesarean section 3, 2, 4.
The lower uterine segment shows an inverse correlation with gestational age, thinning progressively throughout pregnancy 3, 4.
Clinical Relevance in Blighted Ovum
The diagnosis of blighted ovum (anembryonic gestation) at 11 weeks with an 11.1 mm gestational sac is concerning but requires careful interpretation:
A gestational sac measuring only 11.1 mm at 11 weeks gestational age is abnormally small and strongly suggests nonviable pregnancy, as normal gestational sacs should be substantially larger by this gestational age 1.
However, definitive diagnosis of pregnancy failure requires either a mean sac diameter ≥25 mm without an embryo, or follow-up ultrasound demonstrating no embryonic cardiac activity 11-14 days after initial scan showing no yolk sac or embryo 1.
The thickness of the decidua/myometrium itself does not factor into diagnostic criteria for pregnancy viability or failure—the focus should be on gestational sac size, presence/absence of yolk sac, and embryonic cardiac activity 1.
Common Pitfalls to Avoid
Do not confuse decidual thickness with endometrial thickness measurements used in non-pregnant or postmenopausal women (where >11 mm prompts biopsy in asymptomatic postmenopausal women) 5—these are entirely different clinical contexts.
Avoid making definitive diagnoses of pregnancy failure based solely on a single ultrasound measurement unless the mean sac diameter is ≥25 mm without an embryo 1.
The 11.1 mm measurement likely refers to mean sac diameter, not "uterine lining"—clarify what structure was actually measured on the ultrasound report 1.