Serial transvaginal ultrasound scans and β-human chorionic gonadotropin levels in early singleton and multiple pregnancies

To determine if serum β-hCG levels are higher in multiple gestations than in singleton pregnancy at the time of intrauterine sac visualization and the first appearance of fetal heart activity as documented by serial transvaginal ultrasound (US). Prospective analysis of serial transvaginal US findings in 19 pregnancies correlated with serum hCG levels during early gestation. Reproductive endocrinology division of the University of Arkansas for Medical Sciences, Little Rock, Arkansas. Nineteen infertility patients were studied after conceiving. Thirteen underwent IVF or GIFT, 4 received hMG therapy, 1 was treated with clomiphene citrate, and 1 pregnancy followed spontaneous ovulation. Transvaginal US and hCG levels were obtained every Monday, Wednesday, and Friday from 20 to 22days after ovulation until the appearance of fetal heart activity. Initial sac visualization occurred at lower serum hCG levels in singleton versus multiple pregnancies (2,180±1,170 versus 7,028±4,280 mIU/mL, mean±SD). Sacs were always seen when the serum hCG level (mIU/mL) was ≥1,161 in singleton, 1,556 in twin, 3,372 in triplet, and 9,399 in quadruplet pregnancies. Failure to observe an intrauterine sac by transvaginal US in the presence of serum hCG levels in the 1,000 to 2,000 mIU/mL range is not pathognomonic for an ectopic gestation. Clinical symptomatology, risk of multiple pregnancies, and gestational age must also be considered.