There are many factors which make having babies less important or more difficult for young couples than it used to be, including going on to higher education, developing a career, and financial pressures to stay in the job market. Also, many people don’t find a partner they want to have children with until later in life or just don’t feel ready to become parents when they’re younger.

The availability and range of effective contraception has also played a significant part in the trend. This has an impact not only on couples delaying starting a family until they are older, but also on having smaller families.

Age and fertility
Putting off starting a family until your career is established or your debts cleared can have its problems. Fertility falls more sharply for women as they age than for men.

As you can see from the chart below, women are most fertile between the ages of 20 and 24. As women grow older the likelihood of getting pregnant falls steeply while the likelihood of infertility rises sharply. Men can remain fertile for much longer but male fertility still declines with age, albeit less dramatically.

Chart: How Pregnancy rates decline with time

Both of the line graphs are for women who do not have any specific fertility problems.

Source: Management of the Infertile Woman by Helen A. Carcio and The Fertility Sourcebook by M. Sara Rosenthal

Chart: How Pregnancy rates decline with time compared with other body fuctions

How long does it take to conceive?
According to the Human Fertilisation and Embryology Authority, “At 35 you’re half as fertile as when you were at 25; at 40 you’re half as fertile as when you were 35″. This means that it can suddenly take much longer to get pregnant when you hit your late thirties or early forties and you may have problems conceiving at all.

Most couples (92 per cent) will conceive within two years if they do not use contraception and have regular sex. Regular sex means making love every two to three days throughout your cycle; this optimises your chances of conceiving.

That leaves 8 per cent of couples in the general population who do not conceive within two years. If you are over 35 and keep on trying for another year you may still get pregnant but in the next few years your chances of conceiving start to fall rapidly; 6 per cent of women aged 35 years and 23 per cent of those aged 38 years will not have conceived after three years of regular unprotected sex.

This is why it is so important to seek help for infertility treatment sooner rather than later if you are over 35 and finding that positive pregnancy test elusive. It is recommended that most couples try for at least a year before seeking help but if you are over 35 and having problems conceiving you should seek help earlier.

Why does fertility decline so rapidly?
As women get older, there are a number of factors that can make it more difficult to conceive. In addition, as we age, our general health can decline. Existing conditions may worsen or new illnesses may develop, which can impact on fertility too.

Fertility factors that change, as we grow older, include:
• Ovarian reserve – this is the number of functioning follicles left on the ovaries. As you get older you have fewer viable eggs left; in cases of early menopause, the eggs run out much sooner than usual.

• Menstrual cycle – as women approach the menopause their menstrual cycles can become irregular and shorter.

• Lining of the womb – the endometrium may become thinner and less hospitable to a fertilised egg.

• Mucus secretions – vaginal secretions can become less fluid and more hostile to sperm.

• Diseases affecting the reproductive system – some conditions can damage the reproductive organs as time passes, or worsen if not treated properly, including endometriosis, PCOS, and chlamydia.

• Chronic illnesses – some illnesses can have a negative impact on fertility.

• Weight problems – Being overweight or obese can make it more difficult to become pregnant.

Women typically have a decrease in fertility beginning in their early 30s.  On average, a woman in her mid-30s or older will take longer to conceive than a younger woman.  At age 30 to 35, fertility is 15 to 20 percent below maximum.  From age 35 to 39, the decrease is 25 to 50 percent.  From 40 to 45, the decrease is 50 to 95 percent.

Age-related declines in fertility may be at least partly due to less frequent ovulation or to other problems such as endometriosis.  Endometriosis is a condition in which tissue similar to that lining the uterus attaches to the ovaries or fallopian tubes and interferes with conception.

If you are over 35 and trying to conceive, you should see a physician after trying for around six months.  Some studies have shown that about one-third of women between age 35 and 39 and two-thirds of women over 40 have fertility problems.  When they do get pregnant, women older than 35 may have a higher risk of developing gestational diabetes, preeclampsia, and placenta previa. There is also a potentially higher risk of having a baby with low birth weight, and of chromosomal abnormalities such as Down syndrome.

Many cases of infertility can be treated successfully.  While women over age 35 may have more difficulty conceiving, they also have a greater chance of bearing twins. The likelihood of naturally conceived (without fertility treatment) twins peaks between ages 35 and 39.