exposed to the pesticide DDT in the womb could delay a woman becoming
pregnant as an adult, researchers suggest.
chemical has already been linked to premature births and low birthweights.
was banned in the USA and UK around 30 years ago after concerns
were raised over its effects on the environment, animal and human
it is still used in some developing countries to kill malaria-carrying
researchers began following a group of pregnant women in California
in the early 1960s.
took blood samples from them while they were pregnant, and were
then able to follow them and their children through the following
this research, the team from the Centre for Research on Women's
and Children's Health at the Berkeley Public Health Institute looked
at maternal blood concentrations of DDT and DDE, a by-product of
the chemical in 289 women.
then compared them with how long it took their daughters to become
pregnant around 30 years later.
daughters, who were aged between 27 and 31, were asked about the
number of menstrual cycles during which they had used no contraception
to establish the period in which they could have become pregnant.
researchers then devised a "fecundability ratio" in which
the probability of becoming pregnant in each menstrual cycle was
compared with levels of exposure to the DDT.
found the higher the concentrations of DDT in their mother's blood,
the longer it took the daughters to become pregnant.
daughters' probability of becoming pregnant fell by 32% for each
10 microgrammes of DDT per litre of blood.
the daughter's chances of becoming pregnant increased by one- sixth
per 10 microgrammes per litre increase of DDE concentrations in
researchers suggest this may be because DDE offsets the harmful
effects of male hormones called androgens which have been linked
to polycystic ovaries, a cause of infertility.
although DDT may delay pregnancy, DDE may protect against this cause
researchers say this may be why large variations in human fertility
have not been seen since the introduction of DDT.
Barbara Cohn, who led the research, told BBC News Online: "This
is the first scientific report to make a link between DDT and reproductive
impact on women exposed in the womb.
opens up the potential for studying the effect of exposure to many
other substances, such as other environmental chemicals."
said more work would also be needed to see exactly how DDT might
affect the reproductive system.
Cohn added: "While it is reassuring that possible harmful effects
of DDT may be reduced by its conversion to DDE, women still experienced
delays in becoming pregnant.
findings could eventually lead to new understanding about the causes
and prevention of sub-fertility."
Dr Richard Sharpe, a senior scientist at the Medical Research Institute,
told BBC News Online:"This is very interesting and intriguing
it's just not immediately obvious how DDT is exacting that effect."
research is published in The Lancet.