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Grand Rounds

In Twin Pregnancies Does Sex of One Twin Affect Body Size or Gestation Time?

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BACKGROUND AND PURPOSE:

  • Bayraktar et al. (Journal of Obstetrics and Gynecology Canada, 2021) examined the effect of fetal sex of twins and fetal anthropometry and length of gestation in twin deliveries

METHODS:

  • Twin pregnancy study
  • Exposures
    • Male/male twin pregnancies
    • Male/female twin pregnancies
    • Female/female twin pregnancies
  • Primary outcomes
    • Birth weight
    • Head circumference
    • Body length
    • Delivery time

RESULTS:

  • 1028 women with twin pregnancies
    • Male/male: 32.6%
    • Male/female: 33.4%
    • Female/female: 34.0%
  • Discordant twins (male/female pairs) had a higher total birth weight than concordant twins (male/male or female/female pairs; 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 (P<0.001)
    • 0.7 cm longer (P=0.023)
    • 0.4 larger in head circumference (P=0.039)
  • Pregnancies with male/female fetuses had statistically significantly longer gestations, compared to
    • Pregnancies with male/male twins (P=0.003)
    • Pregnancies with female/female twins (P=0.004)
  • Male/male twin pregnancies had the shortest mean gestation time and were at a higher risk of preterm delivery
    • Compared to male/female pregnancies: OR 1.53 (95% CI, 1.07 to 2.19)
    • Compared to female/female pregnancies: OR 1.51 (95% CI, 10.6 to 2.16)

CONCLUSION:

  • For twin pregnancies, the sex of the co-twin affects the other twin’s body size and birth weight
  • Male/male twin pregnancies had the shortest mean gestation time, and had approximately 1.5 times higher risk of preterm delivery
  • The authors state

Although hormonal differences and the effect of testosterone are factors, fetal weight is relatively higher in male than in female fetuses; therefore, the exact mechanism remains unclear

Although some of the differences are clinically minor, they are meaningful 

Learn More – Primary Sources:

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

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Related ObG Topics:

Twin Pregnancy Outcomes Following Confirmation of Viability in the First Trimester
What is the Actual Relative Risk of Preeclampsia in Twins Compared to Singletons?
Planned C-Section or Vaginal Delivery in Twins?

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