Fetal sex contributes to the determination of obstetric outcome, as pregnancies carrying male babies seem to have an increased risk of maternal-fetal complications. Most studies have been conducted on singleton pregnancies, whereas less evidence is available for twins. A 10-year retrospective observational study was conducted on a cohort of 1180 women with twin pregnancy delivered at a single tertiary hospital. Clinical data on maternal characteristics, and obstetric and neonatal outcomes were collected, and the analysis was performed on monochorionic (MC) and dichorionic (DC) diamniotic twins separately. The group of DC twins included 837 cases, and those conceived by assisted reproductive technologies (ART) were more likely to have one or both female fetuses rather than males. The incidence of hypertensive disorders of pregnancy (HDP) was higher in same-sex pairs than in opposite-sex pairs. No differences were found regarding other obstetric and neonatal outcomes among the three sex-pairing groups. The MC twins group included 228 cases, and in female-carrying pregnancies a higher incidence of gestational diabetes (GDM) was observed compared to the male group. Furthermore, male pairs had significantly lower Apgar scores than females. Fetal sex seems to have a mild effect in twins compared to singleton pregnancies, suggesting a more complex set of factors contributing to pregnancy outcome in multiple pregnancies. However, we observed a higher incidence of HDP among same-sex DC pairs, a higher rate of GDM among MC female-female pairs, and a worse adaptation to extrauterine life among male-male pairs in MC twins.

Objective: The incidence of preterm delivery has been increasing, and our aim was to estimate the influence of fetal sex on the risk of preterm delivery in dichorionic twins after spontaneous conception. Methods: 125 spontaneously conceived dichorionic twin gestations, with viable fetuses, born after 24 weeks and delivered spontaneously before 37 weeks, were enrolled. The impact of fetal sex, previous preterm delivery, maternal age, body-mass-index, smoking, and parity on gestational age at birth were evaluated. Results: Despite similar baseline characteristics in all three groups, women with one or two male fetuses delivered significantly more often before 34 weeks than patients with two female fetuses, 48% (23/48) and 43% (19/44) vs 21% (7/33), p = .04. Regression analyses, including fetal sex, maternal age, maternal body-mass-index, smoking, previous preterm delivery and parity, revealed that only fetal sex was significantly associated with spontaneous preterm delivery (p = .03). Conclusion: Fetal sex appears to be a risk factor for preterm delivery in spontaneously conceived dichorionic twin gestations. Twin pregnancies with one or two male fetuses seem to be at higher risk for spontaneous preterm delivery than those with only females.

The objective of this study was to answer the question whether there is the relation between the uterine capacity, estimated by the total birth weight of fetuses, and the duration of twin gestation. The material for researches contains data received from the books of births and case records concerning the pregnant who gave births to twins in the Institute of Obstetrics and Gynecology of the Medical University in Lódź between 1970-1998. The final analysis concerned only gestations lasting more than 29 weeks, without any complications (excluding prematurity and the growth-discordant twins), and when gestational age was exactly known. The selected group was finally composed of 188 pairs of twins. The analyses considered relations between total birth weight of twins, the sex of newborn babies, parity, and the duration of gestation. The duration of the analyzed twin pregnancies was 35,6 weeks, including primiparous with 35,8 weeks, and multiparous – 35,1 weeks. In the group of male-male twin pairs the average duration of pregnancy was 35,7 weeks, in unlike-sexed pairs – 35,6 weeks, and in female-female pairs – 35,5. In the group of the primiparous having male-male twin pairs the average duration of pregnancy was 35,1 weeks, unlike-sexed pairs – 36,4 weeks and female female pairs – 36,6 weeks, while in the group of multiparous relatively: 36,4, 35,4, 35,0 weeks. The total birth weight of the specific pairs of twins was from 2270 g to 6900g (average 4794g), while in 92% <5500g. In the primiparous group it was 4908,1 g. and in the multiparous group – 4663,1 g. Analyzing the total twins' weight according to the fetal gender and parity it was found that in primiparous with male-male twins - 4715,3, unlike-sexed – 5271,6 and female-female – 4967,5, whereas in multiparous relatively: 4961,5, 4692,6, 4414,0. The shortening of twin pregnancies was caused by the following factors: total body mass achieved by fetuses was > 5500 g, presence of male sex in twin pregnancies (only in primiparous), and also the multiparity.

The incidence of preterm delivery was 28.2% of all twin deliveries. Preterm delivery was common in monozygotic twins due to a high incidence of spontaneous rupture of the membranes. In addition, preterm delivery was associated more often with boy rather than girl infants.