The effect of female age on the likelihood of a live birth from one in-vitro fertilisation treatment

In reply: The pregnancies and live births I reported are all attributable to IVF intervention. The physiological and pharmacological reasons for this certainty follow.

Firstly, neither an egg-retrieval treatment nor an embryo-transfer treatment (both of which require hormone administration from the start of menstruation) can be embarked on if a woman is pregnant. This is established not just by the fact of menstrual bleeding, but by showing low levels of oestradiol and progesterone. Thus, no treatment cancellations or retrieval failures were for reasons of pregnancy.

In an egg-retrieval treatment cycle, preovulatory eggs are removed from mature follicles with high efficiency, and so are not available to be ovulated, which virtually precludes natural conception in the retrieval cycle.

As described in my article, transfer of cryostored embryos occurs during a month in which the ovaries are suppressed by the cyclical regimen of ethinyl oestradiol and a progestin (used to develop the endometrium predictably). The effect is that of the sequential oral contraceptive regimens of the 1960s,1 and ovulation is reliably inhibited.

Tonti-Filippini’s estimate of a 25%–30% annual natural pregnancy likelihood with just 12 months’ infertility would be more or less correct for couples in their 20s, but does not pertain to our population (median age, 36 years; median duration of infertility, 3.5 years). The arithmetic that predicts an expected, approximately 5% annual natural conception for such a population is given in Jansen.2

The time during which natural pregnancy could have occurred began with the month after the egg-retrieval cycle and ended, as reported, with the month before either (a) an embryo transfer resulted in a live birth, or (b) the last stored embryo from that retrieval was transferred. There were no natural conceptions that we know of, but, even if there were, such pregnancies would not and could not have been attributed to IVF treatment. Thus, the published figures are reliable.

I reported the implantation rate per embryo for women under the age of 35 as 24.7%. Subtracting the reported 10.5% miscarriage risk yields a live-birth rate of 24.7% minus (24.7% × 0.105), or about 22% per embryo transferred, which is indistinguishable from the expected 20% natural monthly fertility rates among normal couples of this age group.3 Similar calculations yield 11% live births per embryo for those 35–39 years, and 4% live births for those over 40 years. With present practices at Sydney IVF (Day 5 blastocyst transfers, generally single embryos), the chance of a baby per embryo transferred is 41% (< 35 years), 24% (35–39 years) and 12% (> 40 years).

The embryo implantation and live birth data Tonti-Filippini reveals for live births per embryo in Victoria are therefore very low compared with the IVF results I report.