Gestation sac can be seen in ultrasound at:
A. Six weeks gestation
B. Eight weeks gestation
C. Ten weeks gestation
D. Five weeks gestation
Correct Answer: A. Six weeks gestation
Explanation
Gestational sac can be seen on ultrasound at about 4½–5 weeks of gestation.
Explanation
- The gestational sac is the earliest sonographic sign of pregnancy.
- It becomes visible before the embryo or fetal heartbeat.
By type of ultrasound:
- Transvaginal ultrasound (TVS):
- Gestational sac seen at 4.5–5 weeks
- More sensitive and detects pregnancy earlier
- Transabdominal ultrasound (TAS):
- Gestational sac seen at 5–6 weeks
Why this happens
- Early in pregnancy, the embryo is too small to be seen.
- The gestational sac forms first within the uterine cavity and enlarges as pregnancy progresses.
Clinical importance
- Confirms intrauterine pregnancy
- Helps rule out ectopic pregnancy
- Used for early dating of pregnancy
✅ Correct answer: Around 5 weeks (4½–5 weeks on transvaginal ultrasound)
Other Options Details
Below is a general description of fetal/embryonic development at each gestational age, which is commonly asked in obstetrics and embryology exams:
A. Six weeks gestation
- The embryo is about 5–6 mm long.
- Heart is beating and can often be detected on ultrasound.
- Limb buds (upper and lower) appear.
- Neural tube has closed.
- Eyes and ears begin to form.
- The pregnancy is clearly visible on ultrasound.
B. Eight weeks gestation
- The embryo is about 2–3 cm long.
- All major organs are formed (organogenesis complete).
- Fingers and toes are more distinct.
- Face becomes recognizable.
- At the end of 8 weeks, the embryo is now called a fetus.
- Tail disappears.
C. Ten weeks gestation
- The fetus is about 3–4 cm long.
- External genitalia start developing (sex not clearly identifiable yet).
- Head is large compared to body.
- Fetal movements begin (not felt by mother).
- Placenta is well established.
D. Five weeks gestation
- The embryo is about 2–4 mm long.
- Primitive heart tube forms (may just start beating).
- Neural tube formation is ongoing.
- Limb buds are not yet well developed.
- Gestational sac and yolk sac are visible on ultrasound.
Summary Table
Gestational Age Key Features 5 weeks Neural tube, early heart 6 weeks Heartbeat, limb buds 8 weeks Organogenesis complete, fetus formed 10 weeks Fetal movements, genital development
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Writer: Vandita Singh, Lucknow (GS India Nursing Group