July 2003
From European Society for Human Reproduction and Embryology
Women are more likely to suffer recurrent miscarriages if their first child
is a boy
Madrid, Spain: Women who give birth to a boy as their first child are more
likely to suffer subsequent miscarriages than women whose first baby is a
girl, an international conference of fertility experts heard today (Tuesday
1 July).
Dr Ole Christiansen, a consultant registrar at the Rigshospitalet Fertility
Clinic in Copenhagen, Denmark, told the annual conference of the European
Society of Human Reproduction and Embryology, that giving birth to a boy
first was not only a risk factor for subsequent miscarriages, but for women
who suffered unexplained secondary recurrent miscarriages (SRM) it could
mean that they never managed to carry a child to full term again unless
doctors gave them appropriate treatments.
Dr Christiansen said: "Giving birth to a son is known already to be a
prognostically negative factor in many obstetrical complications. Therefore
we wanted to assess the impact of the gender of the first child on the
outcome of subsequent pregnancies among patients with unexplained secondary
recurrent miscarriages.[1]"
He studied 204 SRM patients admitted to clinics between 1986 and 2000, and
obtained information on subsequent pregnancy outcome in 181 patients
admitted before 2000. Among the patients admitted before 2000, only 54.4% of
those who gave birth to a boy in their first pregnancy had given birth to a
second live baby by January 2002, compared with 73% of women whose first
child was a girl.
Amongst a subset of women who did manage to have a second child after a
series of miscarriages, those whose first child was a boy had an average of
3.9 miscarriages before achieving a second birth, while women whose first
child was girl had 3.5 miscarriages before delivery of a second child
65533; a small but statistically significant difference. Average birth
weights of the second children tended to be 181g higher where the first-born
was a girl.
Dr Christiansen said: "Our study shows that the majority (54.4%) of those
who gave birth to a boy in their first pregnancy go on to have a second
child. However this percentage is lower than for those who gave birth to a
girl first. Among my patients I have at least 50 who never have a second
child after the first birth of a boy, whereas approximately 20 patients did
not experience another birth after having a girl. So there are patients who
will never get a second child in both groups, but the risk is larger among
women whose first child was a boy."
He believes that the way women's immune systems react to male foetuses is
the explanation for his finding and that therefore it will be possible to
treat successfully women who suffer from SRMs. "These women may have raised
an immunological reaction against tissue types that are expressed on the
surface of the placenta in pregnancies with boys," he said. "The placenta is
created from the foetus and if it is a boy it will carry these male-
specific tissue types. The mother's immune system may be reacting by forming
antibodies, but also the mother's white blood cells may be reacting against
the placenta."
The first pregnancy is able to proceed to full term because the pregnancy is
safely established by the time the mother's immune system starts to react
to the male foetus. However, it is possible that the immune systems remains
activated after delivery and affects subsequent pregnancies, believes Dr
Christiansen.
"This is an epidemiological study, so we cannot be sure that such an
immunological reaction is the explanation for our findings. However, no
genetic disorder following the known rules of inheritance, can explain the
findings. The impact of the gender of the first-born child on successive
pregnancies is suggestive of something that has memory and only two tissues
in the body are thought to have memory: the central nerve system and the
immune system. Together with a PhD student, I have planned a series of
genetic studies and immunological experiments to confirm or reject the
theory of an impact of male specific antigens on the reproductive
performance of women with SRM."
However Dr Christiansen believes his theory is probably correct because he
has conducted two placebo-controlled trials in which infusions of
intravenous immunoglobulin have been given to women with SRM to try to make
their immune systems tolerate the male-specific antigens. This treatment
increased the live birth rate by a factor of 2.3, whereas no effect could be
detected in women who had never had a child and who suffered recurrent
miscarriages.
"For many years it has been well-known that pregnancies with boys carry an
increased risk for a long series of obstetrical complications compared with
girl pregnancies. We believe that our research will be able to clarify
whether these complications may be related to immunization against male-
specific antigens. If this turns out to be the case, then I believe that we
already have a quite efficient treatment, as our trials have shown."
Abstract no: O-163 (Tuesday, 15.45hrs CET, Paris room)
Notes
[1] SRM is defined as at least three consecutive miscarriages after a
pregnancy that lasted more than