A firstborn boy is suggestive of a strong prognostic factor in secondary recurrent miscarriage: a confirmatory study

OBJECTIVE: To test our previously generated hypothesis that women with secondary recurrent miscarriages with a firstborn boy have a poorer pregnancy prognosis than those with a firstborn girl.

DESIGN: A study of a retrospective and a prospective cohort.

SETTING: The Danish recurrent miscarriage clinic.

PATIENT(S): Two cohorts of 175 and 130 consecutive patients with unexplained secondary recurrent miscarriage referred from 1986 to 1999 (cohort 1) and 2000 to 2005 (cohort 2), respectively.

MAIN OUTCOME MEASURE(S): The odds ratio (OR) for a live birth in the first pregnancy after referral in those with a firstborn boy compared with a firstborn girl in each of the two cohorts. The corresponding OR for a live birth adjusted for relevant prognostic variables in the combined group of patients.

RESULT(S): The crude ORs for a live birth in those with a firstborn boy compared with a firstborn girl were very similar in cohorts 1 and 2 (OR = 0.35, 0.33). In the adjusted analysis only two of five included variables significantly predicted live birth: a firstborn boy and the number of previous miscarriages.

CONCLUSION(S): Male sex of the firstborn child is a strong negative prognostic factor in women with secondary recurrent miscarriage. A possible explanation is an abnormal maternal immune response against male-specific minor histocompatibility (HY) antigens.