Impact of sex on perinatal mortality and morbidity in twins.
OBJECTIVE
Twin studies offer opportunities to investigate mechanisms underlying sex-associated differences in perinatal outcomes. The objective of the study was to investigate sex-related differences in perinatal complications.


METHODS
A cohort of 16,045 twin pregnancies - 32,090 twins - was explored for obstetric complications, perinatal and infant mortality, and neonatal morbidities.


RESULTS
Twin pregnancies with a female fetus had an increased risk for preeclampsia, but otherwise there were no pregnancy complications associated with fetal sex. After birth, female-female twins had lower early neonatal and infant mortality, and lower risk for respiratory morbidities than male-male twins at all gestational ages. In unlike-sexed twin pairs, very preterm males had higher respiratory morbidity than females and, females were at higher risk for being growth restricted.


CONCLUSIONS
Male-male twins have higher respiratory morbidity and neonatal mortality than female-female twins. In unliked-sexed twin pairs, the males seem to be protected by having a female co-twin.
Emma Elsmén
EE
Steen
Karin
K
Källén
Karel
K
Maršál
Mikael
M
Norman
Lena
L
Hellström-Westas
D000328:Adult; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D007234:Infant, Premature; D008297:Male; D007744:Obstetric Labor Complications / Q000453:epidemiology; D054238:Perinatal Mortality; D011247:Pregnancy; D059285:Pregnancy, Twin; D012127:Respiratory Distress Syndrome, Newborn / Q000453:epidemiology; D012727:Sex Characteristics; D012737:Sex Factors; D013548:Sweden / Q000453:epidemiology; D014427:Twins / Q000706:statistics & numerical data*