Up to one in three women experience vaginal bleeding during the first few months of the pregnancy, and many wonder how they can make sure the pregnancy is viable. In a study published in the Obstetrics & Gynecology journal, the authors reviewed records of patients with first-trimester vaginal bleeding who were evaluated with serum beta hCG levels and ultrasound.

Higher hCG levels were associated with a greater proportion of ultimately viable pregnancies.

The authors found that  90% of the time in viable pregnancies one would expect to see the gestational sac at 1,918 mIU/ml, the yolk sac at 5,412 mIU/ml and the fetal pole at 24,599 mIU/ml.

They found that  99% of the time one would expect to see the gestational sac at 3,510 mIU/ml, the yolk sac at 17,716 mIU/ml and the fetal pole at 47,685 mIU/ml.

The "threshold value" the lowest value at which one would expect to see something on ultrasound was:

• Gestational sac: 390 mIU/ml
• Yolk sac: 1,094 mIU/ml
• Fetal pole: 1,394 mIU/ml

This study showed that a viable pregnancy can be diagnosed at lower beta hCG levels and with better ultrasound equipment than previously published.