Wlook for an omen to postpone motherhood they are often encouraged to check their fertility. Although fertility is linked to age, the effect changes over time. Some 35-year-olds find they can’t get pregnant. Others manage on the first try.
The main reasons for declining fertility over the years are reductions in the number and quality of eggs in a woman’s ovaries. Unlike men, who manufacture sperm throughout their post-puberty lives, albeit in ever-increasing quantities, all of a woman’s potential eggs develop while she is still a fetus. A newborn girl has over 1m of them. By puberty, around 400,000 are left. When menopause comes, that’s down below 1,000, and it’s likely to be duds.
But currently available fertility tests do not count the number of eggs left and do not assess their quality. Rather, they rely on an indirect approach – sampling the hormones that are expected to be relevant. Hormone tests are of some value in assessing the timing of menopause and the success of egg retrieval. in vitro fertilization. But predict pregnancy? The evidence suggests they cannot.
Anne Steiner of the Duke Fertility Center in North Carolina doubts it. She suspects that hormone tests indicate how many eggs a woman lays, but that this isn’t the most important thing—it’s the quality of the eggs that matters.
Between 2008 and 2016 Dr Steiner and her colleagues ran the Time to Conceive study. The purpose was to determine whether hormone levels could indeed assess a woman’s fertility, independent of her age. The team then found that those levels had no value in predicting pregnancy in the year after the test. Now, as a follow-up to the original investigation, just published in Fertility and SterilityDr. Steiner has shown that they have no longer-term predictive power, either.
Time to Conceive looked at 750 women aged 30 to 44 who were living with a male partner who was not known to be infertile, who did not have an infertility diagnosis of their own, and who had recently started trying to get pregnant. The team took blood and urine samples from these volunteers and measured levels of three hormones that are often examined through fertility tests. They then followed each volunteer for a year. The upshot, published in 2017, was that hormone levels were uncorrelated with pregnancy within the 12-month window the researchers were looking at.
But perhaps, Dr. Steiner later speculated, that window was too narrow. So in 2020 she contacted the original participants again for a follow-up. She asked them if they would fill in a questionnaire about how many children they had, how long it took them to get pregnant and whether they had been diagnosed with infertility.
336 of them agreed to participate. Among these were 239 pregnancies, resulting in 225 live births. Worse, 73 participants were infertile. But the hormone levels in the tests done in the original study did not predict these results. There was no difference, the researchers found, between women with poor outcomes and those with normal ones.
In the case of one substance, for example – anti-ovulatory hormone, which is considered predictive because it is produced by cells in the ovum-bearing follicles of the ovaries, and is therefore believed to reflect the number of those follicles—79% of those who had low levels of birth. That was statistically indistinguishable from the 71% of mothers who had normal levels. So it is clear that the decrease in fertility, says Dr. Steiner, is not related to the decrease in the quantity of eggs, but probably to their quality. And how to measure that is still unknown. ■