A large percentage of mothers carrying twins in this decade have undergone some type of fertility treatment. Such women tend to be older and the literature is showing that infertile women have a profound increase in spontaneous pregnancy loss even after the early documentation of fetal cardiac activity. In addition, an abrupt increase in spontaneous abortion rates was seen in women over the age of 35 years. A recent study from a perviously infertile population reported a seven percent incidence of spontaneous abortion after the early detection of fetal cardiac activity by transvaginal ultrasonography. Additionally, another study evaluating pregnancy outcomes in 293 pregnancies in previously infertile women with early documentation of fetal cardiac activity reported an incidence of spontaneous pregnancy loss of 11 percent.
Miscarriage also occurs more frequently with increased maternal age in fertile women.
A large study in a fertile population reviewed the transabdominal sonograms of women presenting before 10 weeks of gestation for prenatal care. The overall loss rate after seeing the fetal heart was 2.1 percent. In this study of fertile women, the miscarriage rates ranged from 1.6 percent to 2.6 percent for patients less than 39 years of age. A miscarriage rate of 13.6 percent was noted in patients more than 40 years of age. Ultrasound detection of fetal cardiac activity has been shown to have a higher positive predictive value for viability than the presence of either a gestational sac alone or the use of biochemical markers.