Impact of chorionicity on birth weight discordance in twins

Introduction

Advanced maternal age (AMA; ≥35 years) is becoming increasingly common (1), which may be attributable to older primigravid women postponing childbearing due to lifestyle choices or underlying infertility (2). Advanced age is a risk factor for female infertility and obstetric complications (3), but infertility is a medical problem that can be overcome due to developments in medically assisted reproductive (MAR) therapy. Rates of twin pregnancies have risen substantially over the past 10 years partly owing to increases in average maternal age and advances in the techniques used to improve fertility outcomes (4,5). A significant difference in birth weight in genetically normal twins is referred to as twin birth weight discordance in twins (BWDT) (6), and this phenomenon has been linked to an increased risk of neonatal morbidity in twins (7).

According to some study, chorionicity contributes significantly to the morbidity and mortality of twins (8), with neonatal complications occurring more frequently in monochorionic diamniotic (MCDA) twins (9). In two population-based studies, MCDA twins had a greater rate of newborn morbidity and mortality than did dichorionic diamniotic (DCDA) twins. MCDA twin pregnancies are frequently affected by growth discordance, which can be caused by a variety of reasons, and have poorer outcomes as compared to DCDA twin pregnancies (10). In MCDA twins, placental vascular anastomoses exist between both fetuses, and this leads to 15% of cases being afflicted with twin-to-twin transfusion syndrome, along with hemodynamic imbalance and the discordant growth of the fetuses (11).

Therefore, the aim of our study was to examine the association between twin pregnancies with different chorionicities and BWDT and thus inform the theoretical foundation of twin management. We present this article in accordance with the STROBE reporting checklist (available at https://tp.amegroups.com/article/view/10.21037/tp-2025-5/rc).

Methods

Participants

Complete birth and patient data extracted from the electronic medical records of twin fetuses born in The Third Affiliated Hospital, Guangzhou Medical University, from January 2011 to December 2020 were retrospectively analyzed. There were 4,081 pairs of twins in total, with 498 pairs of MCDA twins and 2,733 pairs of DCDA twins.

This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was reviewed and approved by the Ethics Committee of The Third Affiliated Hospital, Guangzhou Medical University (batch No. 2020; medical review No. 097). Informed consent was signed by the families of all neonates included in the study.

Measures

Definitions

(I) Chorionic character refers to the composition of chorionic and amniotic twins. This study focused on MCDA twins and DCDA twins. (II) Mothers who conceived using in vitro fertilization and embryo transfer (IVF-ET) techniques were placed in the assisted reproductive technology group. (III) Gestational age at delivery was determined according to the definitions of Spong (12) as follows: extremely preterm, gestational age <28 weeks; very preterm, gestational age 28–31⁺⁶ weeks; moderate preterm, gestational age 32–33⁺⁶ weeks; and late preterm, 34–36⁺⁶ weeks. (IV) Low birth weight (LBW) was considered to be a birth weight <500 g; meanwhile, small for gestational age (SGA) was considered to be a birth weight less than the 10th percentile of the weight of a child for the same gestational age, with reference to the birth weight percentile curves for gestational age of twins in the Guangdong Province Line study (13). (V) Birth weight discordance (∆BW) was calculated as follows: ∆BW = (birth weight_big − birth weight_small)/birth weight_big ×100%. A ∆BW >20% was used as the diagnostic cutoff for BWDT (14,15). Twins were divided into the following four groups based on the degree of ∆BW: ≤10%, >10 and ≤15%, >15% and ≤20%, >20% and ≤25%, and >25%.

Grouping

Participants were separated into two groups based on chorionicity: the MCDA twins group and the DCDA twins group. In addition, twins were further divided into heavier and the lighter subgroups based on birth weight.

Data collection

Clinical data of mothers and twins were obtained from the electronic medical record system of The Third Affiliated Hospital, Guangzhou Medical University. (I) Basic information of mothers included age, number of pregnancies, history of adverse pregnancy, method of conception, mode of delivery, gestational week, and complications during pregnancy. (II) Factors related to the birth outcome of twins included gestational age, Apgar score, neonatal respiratory distress syndrome (NRDS), neonatal intensive care unit (NICU) admission of newborns [high-risk infants (16-19) were used as the NICU admission criterion]. (III) Factors related to birth weight included birth weight, SGA or LBW status, ∆BW, BWDT, and degrees of ∆BW.

Statistical analyses

All analyses were conducted with SPSS version 26.0 (IBM Corp., Armonk, NY, USA). The normally distributed measurement data are expressed as the mean ± standard deviation (SD), with the t-test being used to compare groups. Count data are expressed as frequencies and percentages and were analyzed with the χ² test. The association between DCDA and BWDT was analyzed via logistic multivariate regression. P<0.05 was considered to indicate a statistically significant difference.

Results

Comparison of the general features of mothers between the two groups

There was no significant difference in history of adverse pregnancy or mode of delivery between the two groups (P>0.05). However, the proportion of cases with a maternal age ≥35 years old in DCDA group was significantly higher than that in MCDA group (P<0.05), and the primigravid rate in the DCDA group was significantly higher than that in the MCDA group (P<0.001). Moreover, the DCDA group had a greater proportion of mothers who used assisted reproductive technology as compared to the MCDA group, which had a greater frequency of spontaneous conception (P<0.001). The DCDA group had a higher gestational age at birth as compared to the MCDA group (35.48±2.78 vs. 34.94±2.42 weeks; P<0.001) (Table 1).

Comparison of gestation period and complications during delivery between the two groups

The results showed that there was no significant difference in the incidence of premature rupture of membranes, placental abnormality, amniotic fluid abnormality, gestational diabetes mellitus, hypertensive disorders of pregnancy, chorioamnionitis, intrahepatic cholestasis of pregnancy, or hypothyroidism between the two groups (P>0.05) (Table 2).

Comparison of neonatal data between the two groups

Opposite-sex twins were more common in the DCDA group, and male twins and female twins were more common in the MCDA group (P<0.001). The incidence of preterm birth in the DCDA group was lower than that in MCDA group (P<0.001), that of late preterm birth was more common in the MCDA group, and that of full-term birth was more common in the DCDA group (P<0.001). The incidence of NRDS in both twins in the DCDA group was lower than that in the MCDA group (P<0.05). The incidence of both twins being admitted to the NICU in DCDA group was lower than that in MCDA group (P<0.001), while the incidence of neither twin being admitted to the NICU was lower in the MCDA group (P<0.001). There was no significant difference in Apgar score between the two groups (P>0.05) (Table 3).

Comparison of neonatal birth weight between the two groups

Both the heavier and lighter infants in the DCDA group had greater birth weights than did those in the MCDA group (P<0.001). The incidence of LBW in the DCDA group was lower than that in MCDC group (P<0.001), while the incidence of SGA in the DCDA group was lower than that in MCDC group (P<0.05). The incidence of BWDT was lower in DCDA group (P<0.05). The difference in ∆BW degree between the two groups was statistically significant, with the incidence of ∆BW >25% in the DCDA group being lower than that in the MCDA group (P<0.05). However, there was no significant difference in ∆BW between the DCDA group and MCDA group (P>0.05) (Table 4).

Correlation analysis between chorionicity and BWDT

Unconditional logistic regression analysis was used to determine the association between chorionicity and BWDT. When variables of maternal age, number of pregnancies, method of conception, gestational age at delivery, and gender were assumed to be confounding factors that could affect the birth outcomes, it was found that compared with the MCDA group, the DCMC group had a lower risk of BWDT [odds ratio =0.73; 95% confidence interval (CI): 0.55–0.98; P=0.04] (Table 5).

Discussion

Delayed childbearing age, the popularization of gynecologic endocrine therapy, and the promotion of assisted reproductive technology have all contributed to an increase in the rate of twin pregnancies. This trend is particularly pronounced in China, perhaps partly due to the recent introduction of ovulation drugs (20). Twin pregnancy is subject to unique challenges, such as uneven twin development (20). The chorionicity status in twin pregnancies exerts a marked effect on the perinatal prognosis, with monochorionic twins experiencing worse outcomes as compared to dichorionic twins (21). In our study, the incidence of BWDT in DCDA twins was lower than that in MCDA twins.

Mothers ≥35 years old are more likely to use assisted reproductive technology (22). In our study, the vast majority of DCDA twins were conceived by assisted reproductive technology, and the proportion of first pregnancy was relatively high. We speculate that the reason for this may be that assisted reproductive technology is the method of conception in older women with infertility, which is line with other study (23). However, whether chorionic status is related to certain risks in pregnant women is still unknown, but study (20) has reported slightly higher incidences of adverse circumstances in MCDA twins than in DCDA twins, including hypertensive disorder, gestational diabetes mellitus, polyhydramnios, premature rupture of membranes, and abruptio placenta. However, there is an opposite pattern for other indicators, such as severe postpartum hemorrhage. In contrast, we found no significant difference in common complications of pregnancy (including premature rupture of membranes, abnormal placenta, abnormal amniotic fluid, gestational diabetes mellitus, hypertensive diseases during pregnancy, chorioamnionitis, intrahepatic cholestasis, and hypothyroidism) between the two groups examined in our study, which was similar to a previous report (24,25). These discrepancies might be attributable to that the fact the clinical data in our study came from The Third Affiliated Hospital, Guangzhou Medical University, which is the treatment center of high-risk pregnant women in Guangdong Province. The staff in this hospital has extensive experience in the management of difficult and critical pregnancies, scientific prenatal examination, and the diagnosis of chorionic disease in early pregnancy. Individualized pregnancy monitoring interventions can be developed to reduce poor outcomes for mothers and children.

Study has shown that twin pregnancies have a higher risk of adverse outcomes than do single pregnancies (20). Some study have reported that the rate of premature birth in MCDA twins is significantly higher than that in DCDA twins (78% vs. 62.9%) (9), and research in China (26) also suggests that chorionic characteristics are related to premature birth (27). In our study, the DCDA twins group had a lower rate of premature birth and both twins being admitted to the NICU, which is likely related to the vascular structure of the placenta of monochorionic twins. Shared vascular anastomosis branches on the placental surface, hemodynamic imbalance between fetuses, shared placental, imbalance, and abnormal umbilical cord attachment position can lead to differences in pathophysiological changes between the two fetuses, increasing perinatal morbidity and mortality (28). It has been suggested that because premature newborns are underdeveloped, there are greater risks to the neonatal respiratory system, which is reflected in the high incidence of NRDS (29). Therefore, taking into account chorionic status may be critical to managing twin pregnancies and treating abnormal conditions in timely fashion.

Birth weight is an important indicator of neonatal prognosis (30). In our study, the MCDA twins group had a lower birth weight, and the proportion of LBW infants was higher in the MCDA twins group than in the DCDA twins group, which is in line with some other research (31). The incidence of BWDT in our study was 15.5% (32), which is similar to the 18% reported by Amyx et al. (33). The incidence of BWDT in the MCDA twins group was higher than that in the DCDA twins group and consistent with that reported by Park et al. (34). In an Italian study (35), BWD was found to complicate twin pregnancies, compromising neonatal outcomes. The cause of BWDT is not clear, but it may be related to a number of maternal and fetal factors (1). Regarding maternal factors, previous studies have shown that older maternal age, use of assisted reproductive technology (35), MCDA twins (34), and gestational diabetes (20) can increase the risk of BWDT. In agreement with these findings, our study found that the proportion of mothers ≥35 years old and the use of assisted reproductive technology in the DCDA twins group were higher (2). As for fetal factors, the causes of BWDT differ between DCDA and MCDA twin pregnancies due to distinct pathophysiologies. Differences in genetic potential, location of placentation, and placental insufficiency lead to the fetal growth of DCDA twins. Conversely, a hemodynamic imbalance caused by placental vascular anastomoses, an unequal distribution of placental mass, and variances in cord insertion site result in a growth imbalance in monochorionic twins (34). Research in China suggests that this is related to the common vascular distribution, hemodynamic imbalance, and placental imbalance in MCDA twins (36). In our study, maternal age, mode of conception, chorionicity, and other factors jointly affected the incidence of BWDT; even after confounding factors, such as maternal age, were controlled for, it was demonstrated that the risk of BWDT in the DCDA twins group was lower than that in the MCDA twins group.

Conclusions

BWDT was less common in the DCDA twins group than in the MCDA twins group, and there was a lower proportion of NICU admissions in the DCDA twins group, suggesting that DCDA twins experience better pregnancy outcomes than do MCDA twins and have a lower risk of birth weight discordance. To enhance the perinatal outcomes of MCDA twins in the future, it is necessary to identify MCDA twins as early as possible and strengthen perinatal monitoring to improve the perinatal outcome of MCDA twins.

However, as we employed a retrospective design, the indicators included might not have been comprehensive, which might have introduced bias in the results. Therefore, it is necessary to further validate the findings through a multicenter prospective study. Additionally, further evidence is needed to identify the relevant risk factors so that the perinatal outcomes of MCDA twins can be improved.

Acknowledgments

We would like to thank the families of the twins and our colleagues who were involved in this BWDT study.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-5/rc

Data Sharing Statement: Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-5/dss

Peer Review File: Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-5/prf

Funding: This study was supported by the grants from the Guangzhou Science and Technology Planning Project (No. 2023A03J0382) and the Guangzhou Health Science and Technology Project Western Medicine General Guidance Project (Nos. 20231A011087 and 20231A011093).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tp.amegroups.com/article/view/10.21037/tp-2025-5/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was reviewed and approved by the Ethics Committee of The Third Affiliated Hospital, Guangzhou Medical University (batch No. 2020; medical review No. 097). Informed consent was signed by the families of all neonates included in the study.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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