Placental hormone that stimulates progesterone release from the corpus luteum
Useful in the first 6 weeks before confirming an intrauterine pregnancy (not useful after)
Fetal cardiac activity should be visible by 6 weeks on transvaginal ultrasound (TVUS)

Trajectory

Doubles every 2–3 days, peaks at 10 weeks
Red flag: <50% rise in 48 hours suggests abnormal pregnancy (e.g., ectopic, early pregnancy failure)

TVUS Findings Based on β-hCG

Gestational sac visible when β-hCG >1500–2000 IU/L
If non-viable pregnancy suspected: Serial β-hCG q2–3 days + repeat TVUS in 1 week

Monitoring in Failed Pregnancy

Notes

Early pregnancy bleeding + no visible gestational sac → Examine adnexa for ectopic
Adnexal mass (seen in >88% of ectopics) is the most common ultrasound finding
Discriminatory zone: β-hCG level where a gestational sac should be seen (typically 1500–2000 IU/L)
- Below zone: Diagnosis based on inadequate β-hCG rise
- Above zone: Diagnosis based on absent intrauterine pregnancy on TVUS

β-hCG in Pregnancy

Definition and Physiology

β-hCG is a placental hormone produced by syncytiotrophoblast cells that supports the corpus luteum by stimulating progesterone release
It plays a critical role in maintaining early pregnancy until the placenta takes over hormone production

Use and Actions

Essential for confirming early pregnancy status in the first 6 weeks before intrauterine pregnancy can be reliably visualised
Fetal cardiac activity is expected to be visible by approximately 6 weeks of gestation on ultrasound

Trajectory

β-hCG levels typically double every 2–3 days during early pregnancy
Levels peak around 10 weeks of gestation
A rise of less than 50% over 48 hours is a red flag for a non-viable or ectopic pregnancy

TVUS Findings Based on β-hCG

A gestational sac is usually visible on transvaginal ultrasound when β-hCG exceeds the discriminatory zone of 1500–2000 IU/L
In cases of suspected non-viable pregnancy, serial β-hCG measurements every 2–3 days are indicated along with a repeat TVUS in 1 week

Monitoring in Failed Pregnancy

β-hCG should be monitored weekly until levels become undetectable to ensure complete resolution of a failed pregnancy

Notes

In early pregnancy bleeding with no visible gestational sac on TVUS, careful examination of the adnexa is critical to rule out ectopic pregnancy
An adnexal mass is the most common ultrasound finding in ectopic pregnancies, observed in over 88% of cases
The discriminatory zone is key; below this threshold, diagnosis relies on inadequate β-hCG rise, while above this level, absence of an intrauterine pregnancy on TVUS indicates pathology
Serial β-hCG trends help differentiate between viable intrauterine pregnancies, failing pregnancies and ectopic pregnancies
Plateaued or suboptimal β-hCG rises warrant further investigation even if a gestational sac is not visualised
Combining biochemical monitoring with TVUS findings enhances diagnostic accuracy in early pregnancy complications

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