A 4-year retrospective study was conducted on 105 patients exhibiting vaginal bleeding during the first trimester of pregnancy. Cases were selected where the pregnancies were presumed to be viable by ultrasonic evidence of a gestational sac. An attempt was made to clarify the significance of the nidation site in relation to the occurrence of spontaneous abortion or placenta previa. The presence of a discernible gestational sac provided an unusual opportunity to evaluate the therapeutic effect of progestational agents administered in 45 of these pregnancies. Patients with first trimester bleeding had a significantly higher percentage of low implantation sites (25.8%) than the controls (4.8%). Patients with low implantation sites had a similar abortion rate as those with fundal and miduterine implantation sites. Serial scans of the same patient suggest that low implantation is a stage in, rather than a cause of, abortion. None of the 10 patients with low implantation sites progressing beyond 20 weeks' gestation manifested clinical evidence of placenta previa, mitigating against low implantation as a principle cause of this entity. Seventy-three percent of patients with hormonal support aborted an average of 19.7 days after their initial scan, while 66.7% of patients with no hormonal support aborted an average of 4.6 days after their first scan, indicating that progestational agents prolong but do not improve the outcome in threatened abortion. In I case, there was evidence of a gestational sac and subsequent development of a mole supporting the transitional concept for the genesis of hydaditiform mole.
© 1978 The American College of Obstetricians and Gynecologists