Effect of Co-twin Fetal Sex on Fetal Anthropometry and Birth Time in Twin Pregnancies

Published:February 20, 2021DOI:



      This study of twin deliveries aimed to examine the effect of fetal sex and fetal sex of the co-twin on fetal anthropometry and length of gestation.


      Pregnancies were grouped as male/male, male/female, and female/female. Birth weight, head circumference, body length and delivery time of newborns were compared between unlike-sex and like-sex twin pregnancies.


      A total of 1028 pregnant women who met the inclusion criteria were enrolled in the study. Of these pregnancies, 32.6% (n = 335) were male/male, 33.4% (n = 343) were male/female, and 34.0% (n = 350) were female/female. The discordant (male/female) newborns had a higher total birth weight than concordant twins (P = 0.015). Compared with male newborns from male/female twin pregnancies, male newborns from male/male pregnancies were found to be 129 grams heavier, 0.7 cm longer, and had a 0.4 cm larger head circumference (P<0.001, P=0.023, and P = 0.039, respectively). Pregnancies with male/female fetuses had statistically significantly longer gestations than pregnancies with male/male and female/female fetuses (P = 0.003 and P = 0.004, respectively). The shortest mean gestation was observed in the male/male group. Male/male pregnancies had a 1.53 times higher risk of preterm delivery than male/female pregnancies and a 1.51 times higher risk than female/female pregnancies (OR 1.53; 95% CI 1.07–2.19 and OR 1.51; 95% CI 1.06–2.16, respectively).


      This study suggests that, in twin pregnancies, birth weight, head circumference, and body length are affected by the sex of the co-twin. Male sex is associated with shorter gestation and male/male twin pregnancies are at higher risk for preterm labour.



      Cette étude sur les grossesses gémellaires visait à examiner l'incidence du sexe fœtal des jumeaux sur l'anthropométrie fœtale et la durée de la gestation.


      Les grossesses ont été réparties en 3 groupes de sexe fœtal : masculin/masculin, masculin/féminin et féminin/féminin. Le poids à la naissance, le périmètre crânien, la taille et la durée de l'accouchement des nouveau-nés ont été comparés entre les grossesses de jumeaux de sexes différents et les grossesses de jumeaux de même sexe.


      Au total, 1 028 femmes enceintes répondant aux critères d'inclusion ont participé à l’étude. De ces grossesses, 32,6 % (n = 335) étaient du groupe de sexe fœtal masculin/masculin; 33,4 % (n = 343), masculin/féminin; et 34,0 % (n = 350), féminin/féminin. Le poids total à la naissance était plus élevé chez les jumeaux de sexes différents (masculin/féminin) que chez les jumeaux de même sexe (P = 0,015). Comparativement aux nouveau-nés masculins issus d'une grossesse gémellaire masculin/féminin, ceux issus d'une grossesse gémellaire masculin/masculin étaient 129 g plus lourds, étaient 0,7 cm plus longs et avaient un périmètre crânien 0,4 cm plus grand (P < 0,001, P = 0,023 et P = 0,039, respectivement). Une augmentation statistiquement significative de la durée de gestation a été observée pour les grossesses de type masculin/féminin par rapport à celles de types masculin/masculin et féminin/féminin (P = 0,003 et P = 0,004, respectivement). La durée de gestation moyenne la plus courte a été observée dans le groupe masculin/masculin. Le risque d'accouchement prématuré des grossesses masculin/masculin est 1,53 et 1,51 fois plus élevé par comparaison aux grossesses masculin/féminin et féminin/féminin, respectivement (RC : 1,53; IC à 95 % : 1,07–2,19 et RC : 1,51; IC à 95 % : 1,06–2,16, respectivement).


      Cette étude indique que, en cas de grossesse gémellaire, le poids à la naissance, le périmètre crânien et la taille sont influencés par le sexe des jumeaux. Le sexe masculin est associé à une gestation plus courte, et le risque d'accouchement prématuré est le plus élevé en cas de grossesse gémellaire masculin/masculin.


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