IVF Success Statistics Can Be Misleading

A nurse points out the image of a three-month-old fetus during a sonogram scan for Nancy Yin at a clinic in central China's Shaanxi province on Dec. 13, 2010.

Image: Ng Han Guan/Associated Press

After reading a recent Hard Evidence piece about whether fertility "drops off a cliff" at 35, I feel that some hard evidence about the chance of having a baby with IVF is needed. Some of the figures quoted in the article seem overly optimistic as does reporting on IVF at times and this may be because it is not clear what the denominator is. For example, the statement that "pregnancy rates are fairly stable (30-35%) for each embryo transferred up to the age of 30, but fall to 20% by 40 and are only 5% by 45" warrants examination.

IVF treatment involves a number of steps: fertility drugs to develop a number of eggs; retrieving the eggs; adding sperm to the eggs in the hope that embryos develop; and finally an embryo transfer (ET) procedure where an embryo is placed in the uterus in the hope that it will implant and grow into a baby. Unfortunately, there is a risk that things go wrong in each of these steps. The woman might not respond to the fertility drugs, eggs may not be recovered and live birth. embryos may not develop or implant. Even if the embryo does implant and a pregnancy is established, there is also still a risk of miscarriage.

So when we hear IVF success rate figures we need to ask if the rate is per started treatment cycle, per egg collection or per woman who reaches the stage of embryo transfer. Also, "pregnancy rate" is not the same as live birth rate because some pregnancies are lost.

To illustrate the point here are the most recent 2011 statistics about IVF success in Australia and New Zealand:

In that year 40,696 treatment cycles were started. Of these, 37,259 continued to the egg collection stage and 31,053 to the embryo transfer stage. As a result, 9,100 pregnancies were established and there were 6,928 births. So, if "success" is quoted as pregnancies per embryo transfer, the figure is 29%. If on the other hand it is quoted as the chance of a live birth per started cycle, this drops to 17%.

While 17% is a pretty grim figure it is the only honest way of reporting chance of success because what people want and expect when they start an IVF cycle is a live birth.

Then there is the impact that the womans age has on IVF success. The older the woman is the greater the risk at each stage that things wont go to plan. In 2011 the chance of a live birth per started treatment cycle was 25.3% for women aged 30-34 but only 6.6% for women aged 40-44 and a dismal 1.2% for women aged 45 or older. So, while fertility doesnt "drop off a cliff" at 35, the chance of conceiving (spontaneously and with IVF) and having a complication-free pregnancy and a healthy baby steadily declines after age 35 and after age 40 chances are slim.

Of all the women who had IVF in Australia and New Zealand in 2011, 26.5% were aged 40 or older, up from 22.8% in 2007. This means that for one in four women who start IVF, the chance of having a baby is around 6% each time they try. Or, put the other way around, 94 out of 100 attempts will not result in the birth of a baby.

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IVF Success Statistics Can Be Misleading