There is a steady and continuing trend towards later childbearing in all Western European countries. In England and Wales, the fertility rate for women in their thirties has now overtaken that for younger women. Over the last three decades, the average age of women having their first baby has risen and is currently 27.5 in England and Wales. Births to over-35s have shown the steepest rise, more than doubling in the last 20 years, and nine per cent of all first live births are to women in this age group.
These women are the lucky ones; the statistics hide the large number of couples who are unsuccessful in starting a family because they have left it too late. Fertility is usually lost 8-10 years before menopause, and the average age of menopause in Western Europe is 51. Increasing numbers of referrals to Assisted Conception clinics are for older couples, and unfortunately success rates reduce substantially with increasing age of the female partner. In the UK, government-funded IVF is limited to women under 40.
When women do conceive, the risk of miscarriage rises dramatically with age, and at least 50 per cent of pregnancies are lost in the over-40's. The majority are due to genetic abnormalities associated with poor egg quality, and there is a parallel rise in the risk of Down's syndrome which is approximately one in 100 for a woman giving birth at 40.
The outcome of pregnancy is also poorer, with rising stillbirth and neonatal death rates in older mothers. Complications of pregnancy such as gestational diabetes, hypertension, abruption and placenta praevia and pre-term delivery all increase, even though the trend to late motherhood has been led by the healthiest women in higher socio-economic groups. Late first childbirth has also contributed significantly to the rising Caesarean section rate, which reaches 50 per cent for first births over 40.
Ovarian failure remains an untreatable condition. Egg donation transforms the chance of pregnancy, but of course the child is genetically unrelated to the woman. Moreover, egg donation is not available in all countries as regulations vary widely, and it is highly expensive and thus unattainable for many couples.
A novel strategy for preserving the opportunity of fertility is for young women to freeze their eggs. Subsequently the oocytes can be thawed, fertilised (using intra-cytoplasmic sperm injection) and transferred to the uterus. The first human live births resulting from previously frozen oocytes date from the late 1980s, but the initial results were poor and the technique was not taken up again until the late 1990's. The world literature suggests that a live birth rate of 10 per cent is a reasonable estimate; however, recent reports indicate that the live birth rate may not be far below that of frozen embryos.
At present this technology is usually offered to young women about to undergo chemotherapy or radiotherapy for cancer, which will render them menopausal. Some couples going through IVF may choose to cryopreserve spare oocytes instead of supernumerary embryos for religious or ethical reasons. In Italy the restriction on embryo freezing and the limitation on number of eggs to be fertilized has driven the need to develop oocyte freezing. An increasing number of women are turning to Assisted Conception units for egg freezing for social reasons; they are keen to preserve their chance of having children but have not found a partner and are aware that time is running out. The demand for egg freezing is certain to increase.
The reasons for delayed parenthood are complex. More women have entered higher education and seek satisfying career development; there is good availability of effective contraception, backed up in some countries by safe legal abortion; young people seek to achieve financial security before embarking on parenthood; there is a higher incidence of breakdown of relationships. These issues deserve further sociological research.
Women may not be aware of the difficulties and dangers of late pregnancy, the delay in conceiving, the risk of miscarriage and chromosomal abnormality. The media contain very positive images of celebrities enjoying late motherhood (with or without assistance), but little on its risks. We need to make information available to women on their fertility, and how it declines with age. Perhaps the education system needs to take responsibility for this. There are very few decisions more important than having children. Education is essential, and providing information on the medical consequences of delayed conception may help couples to plan their lives, to have children in the safest years from 20 to 35, and avoid the heartbreak of infertility and pregnancy loss.