The chance of a successful pregnancy declines considerably in women aged more than 35 years, irrespective of her reproductive history, according to new research in this week's British Medical Journal.
Danish researchers analysed the combined effects of maternal age and reproductive history on outcome of pregnancy in over 600,000 women between 1978 and 1992. They found that more than one fifth of all pregnancies in 35 year old women was unsuccessful - due to spontaneous abortion, ectopic pregnancy or stillbirth - and at 42 years of age more than half of the intended pregnancies was unsuccessful.
The risk of a spontaneous abortion varied from a minimum of 8% by the age of 22 years to over 84% by the age of 48 years or more, irrespective of previous reproductive problems. Similarly, the risk of an ectopic pregnancy also increased with increasing maternal age, from 1.4% of all pregnancies at the age of 21 years to 6.9% in women aged 44 years or more. Interestingly, the risk of stillbirth was still higher among women aged more than 35 years, but to a lesser extent than for spontaneous abortion and ectopic pregnancy.
These findings, say the authors, indicate that postponing pregnancy will increase the level of unsuccessful pregnancies and possibly the costs of health care. They conclude that women should be counselled more fully to ensure that these risks are taken into consideration when making decisions about reproduction.
In an accompanying editorial, researchers at Columbia University add that other aspects of reproduction, such as multiple births and congenital malformations, should also be considered by potential older parents yet are often beyond the scope of routine records. However, on a positive note, they suggest that a child born to older parents does have advantages. For instance, their experience and knowledge are bound to be greater than younger parents and their economic situation better. "Biological disadvantage is to a degree balanced by social advantage," they conclude.