Placenta previa: Preponderance of male sex at birth

To determine the relation between placenta previa and male sex at birth, th e authors conducted two types of analysis: 1) a historical cohort analysis of singleton live births in New Jersey hospitals during 1989-1992 (N = 447, 963); and 2) a meta-analysis of previously published studies on the subject , For the cohort analysis, subject mother-infant dyads were identified from linked birth certificate and maternal and infant hospital claims data. The infant's sex for mothers with an international Classification of Diseases, Ninth Revision, Clinical Modification, code of 641.0-641.1 for placenta pr evia (n = 2,685) was compared with infant's sex for mothers without placent a previa (n = 445,270), For the meta-analysis, seven published articles wer e located and summary effects were calculated using both fixed-effect and r andom-effects models. In the present cohort study, the male:female ratio at birth was significantly higher in women with placenta previa (1.19) than i n those without placenta previa (1.05) (p < 0.001), The association of plac enta previa with male sex persisted when the analysis was either stratified or adjusted for the effects of maternal age, maternal parity, maternal smo king during the index pregnancy, race/ethnicity, the infant's gestational a ge, and the infant's birth weight. The meta-analytic results from the fixed -effect and random-effects models showed a 14% excess of placenta previa wh en women were carrying a viable male fetus as compared with a viable female fetus during pregnancy. The results were the same regardless of whether th e present cohort study was included in the meta-analysis, In conclusion, th e evidence obtained from these analyses strongly argues for an association between placenta previa and male sex at birth. The mechanism for this assoc iation remains to be determined.