Study finds Rh factor not linked to GBS status. (Large Retrospective Analysis).

BANFF, ALTA.--Pregnant women who are Rh-factor negative don't appear to be at higher risk of group B streptococcus colonization than their Rh-positive counterparts, Dr. Philip Mead said at the annual meeting of the Infectious Diseases Society for Obstetrics and Gynecology.

That's reassuring news, but it's not necessarily the end of the story. New evidence still needs to be reconciled with earlier reports showing that Rh-negative women were twice as likely as Rh-positive patients to be colonized with group B streptococcus (GBS), said the professor and chair emeritus of ob.gyn. at the University of Vermont, Burlington.

In a retrospective study, Dr. Mead and his colleagues investigated database records for 7,652 women who delivered at the university hospital from Jan. 1, 1998, through December 2001 . Specimens were collected for culture by separate swabs of the vaginal introitus and anorectum at 3537 weeks' gestation. A total of 1,951 women (25%) were GBS colonized and 5,701 were GBS negative. There was no relationship between GBS colonization rates and Rh status among the 6,423 Rh-positive and 1,229 Rh-negative patients. About 25% of each Rh group was colonized.

There also was no relationship between ABO blood groups and colonization rates.

Dr. Mead said that that the initial concern about blood type and GBS risk arose with a 1978 study showing that women with blood type B were twice as likely to be colonized with GBS and that their colonized newborns were more likely to develop neonatal GBS than those born to women with A or O blood types. Blood type B was detected in 16% of the total population but in 30% of the colonized infants.

The investigator for this study was so convinced of the relationship between blood type and GBS risk that she suggested blood group B be considered a new risk factor for colonization with GBS.

In 1980, however, Dr. Mead and his colleagues found no association between ABO blood group ...