Monday, August 06, 2007

Baby boys raise future miscarriage risk

Mothers whose first child is a boy are then more likely to suffer recurrent miscarriages than those bearing a girl first, suggests a new study.

Baby boys are already known to be more taxing for mothers, requiring more energy during gestation and being heavier at birth than girls. But the researchers believe a fundamental immune response from the mother to foreign male antigens or proteins is to blame for the miscarriage link.

Ole Christiansen, a consultant registrar at the Rigshospitalet Fertility Clinic in Copenhagen, Denmark, and colleagues carried out an epidemiological analysis of 181 women with secondary recurrent miscarriage admitted to clinics between 1986 and 2000. Secondary recurrent miscarriage describes a scenario in which a woman has at least three failed pregnancies after giving birth a first time.

For women whose first baby was a girl, 73 per cent had given birth to another living child by January 2002. In contrast, only 54 per cent of women who had given birth to a son in their first pregnancy had a second baby.

The researchers also found that, among the women who did have second babies, those who had boys first suffered an average of 3.9 miscarriages before their second child arrived. Those who had a daughter first suffered an average of 3.5 miscarriages before the second child - a small but statistically significant difference.

Immunological reaction
But in some cases, a second baby never arrives. "Among my patients, I have at least 50 who never have a second child after the birth of a boy, whereas approximately 20 patients did not experience another birth after having a girl," Christiansen told New Scientist.

He says some women may suffer a raised immunological reaction against tissue types expressed on the surface of the placenta in a pregnancy with a boy, as the placenta is created from the fetus.

"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," he says. If this is correct, the first pregnancy would sensitise the mother's immune system and cause it to react more strongly in subsequent pregnancies.

For similar reasons bone marrow transplants from a sister to a brother are known to be much riskier than from a brother to a brother, he says, and this risk is even greater if the sister has previously been pregnant.

Christiansen presented the findings at the European Society of Human Reproduction and Embryology's annual meeting in Madrid on Tuesday.


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