Age and reproductive outcomes

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Produced by The Fertility Society of Australia: Pre-Conception Health Special Interest Group and Your Fertility
Last updated June 2016

Fertility declines with age, so if you are thinking about having a baby, consider trying sooner rather than later. Here are some facts about how age affects women’s and men’s fertility and their chance of having a healthy baby.

Age and fertility

Female and male fertility decrease with age. For women fertility starts to slowly decline when they are in their early thirties. Around age 35 the decline speeds up and by age 40 the chance of conceiving has fallen by half. The biological reason for this is that, as women age, the total number of eggs in their ovaries and their quality decline. The average age of menopause is about 51 years
(and this has not changed over the centuries) and this marks the absolute end of fertility but in fact, it is rare for a woman to conceive in the 10 years leading up to menopause. In part this is because the quality of the eggs that are released is compromised; at age 40 about 75% of eggs are chromosomally abnormal which reduces the chance of pregnancy and increases the risk of miscarriage.

While many women in their late thirties and early to mid-forties give birth to healthy babies, it is an undisputable fact that increasing age (beyond age 35) reduces a woman’s likelihood of conceiving and giving birth. Here are some facts about the relationship between female age and fertility:

– the monthly chance of conception decreases from 20% for women aged 30 to 5% for women aged 40

– the risk of chromosomal abnormalities in the fetus increases from 1 in 385 in women aged 30 to 1 in 63 in women aged 40

– less than 10% of women in their early twenties experience pregnancy loss compared with more than 50% of women aged 42 or more.

In men the fertility decline starts later and is more subtle. But it does happen. Women in couples where the man is over the age of 45 take five times longer to conceive than those where the man is in his twenties.

Age and IVF success

IVF can help people with infertility have a family but the technology cannot make up for the natural decline in fertility that happens as women get older. Based on a report of almost 200,000 women in the UK who had IVF between 1999 and 2007, the chance of having a baby after three IVF treatment cycles, including the transfer of any frozen embryos, for different age groups were:

Age and fertility table
These figures apply to women who use their own eggs. If an older woman uses eggs from a younger donor, her chance is the same as that of a woman in the donor’s age group.

Age and pregnancy health

The proportion of pregnancies that miscarry increases with age. The risk of miscarriage is 10% at age 20 and 90% among women aged 45. Women whose male partner is aged over 45 are twice as likely to miscarry as those whose partner is in his twenties.

The risk of pregnancy complications also increases with age. While they are still rare complications, the risk of gestational diabetes, placenta praevia (when the placenta covers part of or the whole cervix which increases the risk that it detaches), caesarean section, and still birth increase after age 35.

Age and the new baby

Because of changes in eggs and sperm that occur as we age, children of older parents have a slightly higher risk of birth defects, chromosomal abnormalities and autism spectrum disorder. However, it is important to remember, that although the risk increases, most babies are born healthy, irrespective of their parents’ age. It is estimated that the risk of a baby having a chromosomal abnormality is approximately 1 in 400 for a woman aged 30 and 1 in 100 for a woman aged 40.