Several reports have suggested that pregnancies conceived by assisted reproductive technologies (ART) have an increased risk of spontaneous abortion. These reports are difficult to evaluate because of the differences in definitions used and the compounding of other risk factors, particularly maternal age and pelvic abnormalities. Schieve and colleagues used data collected from more than 62,000 pregnancies resulting from ART to establish the risk for spontaneous abortion.

The data were gathered as part of mandated reporting to the Centers for Disease Control and Prevention about every ART procedure in the United States. The study concerned 181,340 ART embryo transfers during 1996, 1997, and 1998 in women 20 to 55 years of age. Uterine pregnancy documented by sonography resulted from 63,855 (35.2 percent) of the procedures. The outcome of these pregnancies was established by follow-up with the patient or her obstetric professional. Data were available on 62,228 pregnancies.

The overall spontaneous abortion rate was 14.7 percent; however, this rate varied with the age of the mother and the source of the oocyte. The spontaneous abortion rate ranged from 10.1 percent in women 20 to 29 years of age to 39.3 percent in women older than 43 years who conceived using their own oocytes. When donor eggs were used, the rate—13.1 percent—varied little with maternal age. The methods associated with the highest rates of spontaneous abortion were those using frozen and thawed embryos. Women younger than 30 years who conceived using their own oocytes and freshly fertilized embryos had a 10 percent spontaneous abortion rate, but this rate tripled if the mother was 40 years or older. Other factors associated with an increased rate of spontaneous abortion were a history of spontaneous abortions, multiple ART attempts, use of clomiphene, and surrogate pregnancies.

The authors conclude that spontaneous abortion rates in patients using ART and their own oocytes and freshly fertilized embryos were slightly lower than the expected spontaneous abortion rate in women of comparable age. The quality of the oocyte or embryo is critical to success following ART.