Placenta Previa: Preponderance of Male Sex at Birth

Abstract

To determine the relation between placenta previa and male sex at birth, the 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 previa (n = 2,685) was compared with infant's sex for mothers without placenta previa (n = 445,270). For the meta-analysis, seven published articles were located and summary effects were calculated using both fixed-effect and random-effects models. In the present cohort study, the male:female ratio at birth was significantly higher in women with placenta previa (1.19) than in those without placenta previa (1.05) (p<0.001). The association of placenta previa with male sex persisted when the analysis was either stratified or adjusted for the effects of maternal age, maternal parity, maternal smoking during the index pregnancy, race/ethnicity, the infant's gestational age, 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 when women were carrying a viable male fetus as compared with a viable female fetus during pregnancy. The results were the same regardless of whether the present cohort study was included in the meta-analysis. In conclusion, the evidence obtained from these analyses strongly argues for an association between placenta previa and male sex at birth. The mechanism for this association remains to be determined.

Fetal sex and perinatal outcomes

“…The associations between placenta previa and male sex were maintained after the results were adjusted for maternal age, parity, smoking during pregnancy, race, gestational age and birth weight [4] . In the present study the only difference that was statistically signifi cant was the higher frequency of umbilical cord alterations (true knots and nuchal cord).…”

Sex and gender differences in newborn infants: why are boys at increased risk?

“…Furthermore, preterm rupture of membranes, polyhydramnios, infection and placental abruptio, appear to occur more frequently when the fetus is male [22,23]. Placenta previa has also been reported to be more common in women carrying male fetuses [24]. Male fetuses seem to be more severely affected by maternal alloimmunization to D-antigen, male fetal gender was associated with a need for earlier and more intrauterine blood transfusions, and male infants had higher neonatal mortality [25].…”

Risk factors for placenta previa in an Asian population

“…Although the etiology of placenta previa remains speculative, several risk factors associated with this condition have been established. These include advanced maternal age, multiparity, multiple gestation, smoking during pregnancy, a male fetus, previous abortion, previous cesarean delivery, and placenta previa in a previous pregnancy [1,2,4,7,9–11].…”