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Understanding Fertility Success Rates

Patients ask for advice on understanding fertility success rates.

When reviewing the Fertility Clinic Summary Report published by SART and the CDC, it is important to understand exactly what you are reading.

Different practices may take care of different types of patients, and we are all specifically instructed to remind our patients that both SART and the CDC state that it is not scientifically valid to compare the results of different practices to one another. The official CDC report contains an overview of the data as well as an explanation of the clinic-specific reports. In addition, a National Clinic Summary Report from SART is available by visiting their website This report also provides data for each of the clinics that report to SART.

Reported age groups in fertility success data

When one reviews either the CDC or SART reports, it is important to critically review the statistics for the appropriate age groups that is displayed across the top of the columns of numbers. These age groups are:

  • <35
  • 35-37
  • 38-40
  • 41-42

Once a couple locates the age group of the female partner, the relevant numbers (which are percentages) can be found under the appropriate column. The categories that are most important to examine include; the number of cycles performed by a program in a given year, the percentage of retrievals resulting in live births, the percentage of transfers resulting in live births, the implantation rate and the average number of embryos transferred.

Many of the categories are self-explanatory. For example, the Percentage of Retrievals Resulting in Live Births indicates how many of the patients in an age group who underwent egg retrieval actually delivered a child, divided by the total number of patients in that age group who underwent a retrieval.

Other categories require some explanation

The Percentage of Transfers Resulting in Live Births
This data does not include the patients who had egg retrieval but did not have an embryo transfer. Some of these patients underwent egg retrieval in order to freeze their eggs. Other patients underwent egg retrieval but did not undergo an embryo transfer because their oocytes failed to fertilize, or if they did fertilize, their embryos failed to develop. Some patients may have had good quality embryos but did not undergo the embryo transfer because of a family emergency, a medical complication, or they were at high risk of developing a complication such as ovarian hyperstimulation syndrome.

The Implantation Rate
This data indicates the percentage of the embryos that were transferred to the patient’s uterus that actually implanted. Programs such as ours that have high pregnancy rates typically transfer fewer embryos in the hope of avoiding higher order multiple pregnancies (greater than twins).

The Average Number of Embryos Transferred
The number of embryos transfer should be low for younger patients and higher for older patients. SART has a recommended number of embryos to transfer for each age group. If the female is <35 years of age, SART recommends the transfer of 1-2 embryos. Women who are 35-37 should have 2-3 embryos transferred. Women 38-40 should have 3-4 embryos per transfer. After age 40, SART recommends up to 5 embryos per transfer.