H. Svarre Nielsen1, A.M. Andersen Nybo2, O.B. Christiansen1 1The Fertility Clinic - Section 4071, Obstetrics and Gynaecology, Copenhagen O, Denmark 2 National Institute of Public Health, The Childrens Programme, Copenhagen O, Denmark
Introduction: Sex-mismatch between donor and recipient is correlated to a poorer prognosis in transplantation medicine. A significantly higher frequency of Graft Versus Host Disease (GVHD) is seen when sisters with a pregnancy history donate bone marrow to their HLA identical brother. It is believed that women in pregnancies with boys become primed against HY-specific minor histocompatibility antigens (HY) that are only present in males. When bone marrow from these women is introduced in the male recipient an immune response against HY is established and causes the increased frequency of GVHD. We have previously reported that a first-born boy is associated with a less favourable reproductive potential among patients with secondary recurrent miscarriage (SRM) referred to the Danish Recurrent Miscarriage Clinic between 1986-2000 and followed up to 14 years. Here, we aimed, with an extended study population, to quantify the impact of a first-born boy on the live-birth rate in the first pregnancy after referral adjusting for relevant prognostic factors in patients with SRM. We focused only on the first pregnancy after referral to get an exact estimate of the effect without influence of reproductive compensation.
Material and Methods: Pregnancy outcome information on the first pregnancy after referral was procured in two groups of SRM patients referred to the Danish Recurrent Miscarriage Clinic between 1986 and 1999 (cohort 1) and between 2000 and 2005 (cohort 2), respectively. Live birth as the outcome variable was analysed in a logistic regression analysis with the following explanatory variables: first-born boy, age, no. of miscarriages, change of partner, and treatment.
Results: Significantly more of the 276 patients had had a first-born boy compared to a first-born girl both in cohort 1 and 2 (p=0.01). In cohorts 1 and 2, 54% and 66% of patients with a first-born boy had a subsequent live birth, compared to 75% and 81% of those with a first-born girl. Among the 221 patients who became pregnant after referral, the only two variables significantly predicting live birth were a first-born boy OR: 0.43 (0.2-0.8), p=0.007 and the number of previous miscarriages OR: 0.73 (0.6-0.9), p=0.013.
Conclusions: Sex of the first-born child is the most important prognostic factor in women with SRM followed by the number of previous miscarriages. The correlation between a first-born boy and a poorer prognosis might be explained by a maternal immunological reaction towards male specific HY.