The Centers for Disease Control and Prevention (CDC) has released its report on assisted reproductive technology (ART) procedures conducted in the United States in 2002. Data for the report were collected from nearly all U.S. medical centers that provide fertility treatment, as mandated in 1992 by the Fertility Clinic Success Rate and Certification Act. Analysis was carried out by treatment type (e.g., patient or donor egg, freshly fertilized or thawed embryo, number of embryos transferred) and patient characteristics (e.g., age, diagnosis, previous births or procedures). The findings will help prospective parents make informed decisions about treatment.
More than 115,000 ART procedures were performed in the United States in 2002, resulting in the births of 45,751 infants. Because transfer of multiple embryos remains common, more than one half of infants born through ART are from multiple births, compared with 3 percent in the general population, and ART-born infants account for around 17 percent of all multiple births. The substantially increased risks of multiple births, such as hemorrhage and hypertension in the mother and low birth weight, mortality, and long-term disability in the infants, must be taken into account when considering the use of ART treatment. In 2002, about 95 percent of triplets and higher multiples born through ART had a low birth weight, compared with 9 percent of single-birth infants; 97 percent of triplets and higher multiples were born preterm, compared with 15 percent of single-birth infants.
Rates of pregnancy, live birth, and multiple births varied with patient and treatment factors. According to the CDC report, procedures using freshly fertilized embryos and donor eggs yielded the highest rates of multiple births (42 percent), followed by procedures using freshly fertilized embryos and the patient’s own eggs (35 percent). Procedures using freshly fertilized embryos and donor eggs had around double the rates of pregnancy, live birth, and single-infant birth (58, 50, and 29 percent, respectively) compared with procedures using thawed embryos and the patient’s own eggs.
Factors strongly associated with risk of multiple births included number of embryos transferred and patient age. In women who used freshly fertilized embryos from their own eggs, the most common procedure—transfer of two or more embryos—increased the chances of live birth and the risk of multiple births; this risk varied with the patient’s age. Rates of live birth and multiple births increased with the number of embryos transferred in women 41 to 42 years of age, and were higher with transfer of three or more embryos in women 38 to 40 years of age. Women 37 years or younger had higher single-birth rates with transfer of two embryos than with three.
Rates of live birth and multiple births in women who used freshly fertilized embryos from their own eggs decreased as patient age increased. Live birth rates decreased from 43 percent in women younger than 35 years to 7 percent in women older than 42 years (from 26 to 6 percent, respectively, for single birth). Multiple birth rates decreased from 39 percent for women younger than 35 years to 7 percent for those older than 42 years.
The CDC report states that ART is a major risk factor for multiple births, and that efforts should be made to limit the number of embryos transferred. In most instances this would minimize the risk of multiple births without lowering the chances of success, especially for younger women. For this to become general practice, however, patients and physicians need to view treatment success in terms of single-infant pregnancies and births, which are measures of better patient outcomes.
The report cautions that because the data are recorded by procedure rather than by patient, the analysis does not account for those patients whose attempts at pregnancy fail and who undergo more than one treatment per year; thus, the report may underestimate the per-patient success rate.