Relationship of initial chorionic sac diameter to abortion and abortus karyotype based on new growth curves for the 16th to 49th post-ovulation day.

In order to determine whether initial chorionic sac diameter is related to subsequent abortion, abortus karyotype, or birth weight and length, chorionic sac diameter was prospectively measured by transvaginal ultrasound in 700 singleton pregnancies before post-ovulation day 31, the latest day cardiac activity becomes detectable in normal pregnancy. Results were compared to values for the 10th to the 90th centiles, determined from 227 measurements of in-vitro fertilization and gamete intra-Fallopian transfer pregnancies. The abortion rate was 23.9% [95% confidence interval (CI) 19.2%, 28.6%] when initial chorionic sac diameter was below the 50th centile, compared to 6.9% (95% CI 4.9%, 9.4%) when equal to or above the 50th centile. Chorionic sac diameter was below the 50th centile in all anembryonic abortions and in 62% of embryonic abortions. Triploidy, trisomy 47 + 16, or trisomy 16 and the presence of satellite bodies on chromosome 22 were the only abortus karyotypes significantly associated with small chorionic sac diameter. Initial chorionic sac diameter was not associated with birth weight or length. We conclude that chorionic sac diameter is decreased in anembryonic and embryonic abortion and that normal pregnancy outcome may be expected in 90-95% of pregnancies in which initial chorionic sac diameter is equal to or above average.