In Vitro Fertilization and Dichorionic-Diamniotic Twin Pregnancies in Nulliparous Women: A Retrospective Cohort Study Comparing Pregnancy Outcomes Between Advanced and Younger Maternal Age Groups

Introduction

In recent years, the number of nulliparous women at advanced maternal age in China has steadily increased, driven by economic development and changing marital attitudes. This demographic shift, combined with the widespread use of Assisted Reproductive Technology (ART), has consequently led to a surge in twin pregnancies in nulliparous women at advanced maternal age. Advanced maternal age is defined as being 35 years or older at the time of the first delivery.¹ Globally, the proportion of women delaying childbirth until their late 30s or early 40s has significantly risen.² The literature indicates that the incidence of twin (or multiple) pregnancies resulting from assisted reproductive technology can reach as high as 21.8%.³ Twin pregnancies are associated with a higher risk of complications compared to singleton pregnancies, including hypertensive disorders, diabetes, postpartum hemorrhage, and preterm birth.⁴ A meta-analysis has demonstrated that, although perinatal outcomes are comparable between women of advanced maternal age and younger women with twin pregnancies, the advanced maternal age group exhibits a significantly higher incidence of gestational diabetes and cesarean deliveries.⁵ A study conducted in South Korea found that twin pregnancies in older mothers are associated with an increased risk of gestational diabetes, placenta previa, and higher neonatal birth weight; however, other outcomes did not show a significant correlation with maternal age.⁶ Additionally, a domestic study reported that twin pregnancies in women of advanced maternal age are associated with higher risks of preeclampsia, gestational diabetes mellitus (GDM), postpartum hemorrhage (PPH), and preterm birth (PTB), although the risk of adverse neonatal outcomes did not increase significantly.⁷ In IVF twin pregnancies, the mothers are usually older, and the proportion of nulliparous women is higher.⁸ Some literature studies have shown comparisons of outcomes between different age groups (such as the increased risks in advanced maternal age vs younger maternal age).^9,10 Despite these findings, there remains a notable lack of research specifically focusing on the outcomes of DCDA twins pregnancies in AMA nulliparous women undergoing IVF. This gap is particularly concerning given the unique risks associated with this subgroup. This study aims to analyze the impact of advanced maternal age on the outcomes of DCDA twins achieved through IVF in nulliparous women. By focusing specifically on DCDA twins in this demographic, we aim to fill a critical gap in the literature, as existing studies predominantly focus on singleton pregnancies or mixed chorionicity twins. By providing clinical evidence, we hope to inform the perinatal management of advanced maternal age nulliparous women and potentially contribute to the development of targeted clinical guidelines for this population. Nulliparous women may have different baseline characteristics compared to multiparous women, such as no prior birth history, which reduces confounding factors. For instance, previous studies have used nulliparous women cohorts to isolate the effects of age or other variables on the outcomes of twin pregnancies.^9,11 By providing clinical evidence, we hope to inform the perinatal management of advanced maternal age nulliparous women. By comparing outcomes between women of advanced maternal age and younger maternal age nulliparous women, we seek to offer more scientific guidance for clinical practice. We hypothesized that AMA nulliparous women with DCDA twins would exhibit higher rates of growth discordance and obstetric hemorrhage to younger counterparts, independent of confounders addressed through propensity matching. However, existing studies predominantly focus on singleton pregnancies or mixed chorionicity twins. The specific risks associated with DCDA twins in AMA nulliparous women undergoing IVF remain underexplored, particularly regarding growth discordance mechanisms.

Patients and Methods

General Information

Our study was conducted in a city with 13 tertiary hospitals. The center reports an annual delivery volume of approximately 3000 cases, which includes a diverse population of young primiparous women, women of advanced maternal age (AMA), and women with multiple gestation. To ensure the validity of our findings, we established strict inclusion criteria for patient enrollment. These criteria were designed to minimize selection bias and to focus on specific patient populations relevant to our research objectives. Only patients who met these criteria were included in the study, allowing us to draw meaningful conclusions from our data.

This study included nulliparous women who underwent cesarean section for IVF dichorionic-diamniotic twin pregnancies at the Second Nanning People’s Hospital from January 2020 to August 2024. All data were extracted from standardized electronic medical records, including prenatal visit logs, laboratory reports, and surgical notes. The advanced maternal age group consisted of 47 cases, while the younger maternal age group comprised 94 cases. Flowchart of Study Population Selection (Figure 1).

Figure 1 Flowchart of Study Population Selection.

Inclusion and Exclusion Criteria

Inclusion criteria: IVF; DCDA; nulliparous women; timely prenatal check-ups (defined as attending ≥8 scheduled prenatal visits with complete documentation of fetal biometry and Doppler studies, excluding preterm births). Exclusion criteria: Other types of twin pregnancies; congenital fetal abnormalities; stillbirth of one twin; heart disease; severe anemia; immune-related diseases; Suboptimally Controlled Diabetes; Suboptimally Controlled Hyperthyroidism; Suboptimally Controlled Chronic Hypertension; incomplete clinical data.

Method

Methods and Observational Indicators

Participants were divided into two groups: advanced maternal age group (≥35 years) and younger maternal age group (20–34 years). We compared BMI, pregnancies, age at menarche, gestational age at delivery, PTB, PROM, LBW, discordant twin growth, intraoperative blood loss, hemoglobin levels in early and late pregnancy (early pregnancy defined as before 13 weeks, late pregnancy as the most recent result before delivery), placenta previa, placental abruption, HDP, GDM, ICP, and PPH.

This study has received approval from the Ethics Committee of the Second Nanning People’s Hospital, which granted a waiver for informed consent from participants because the research involves retrospective analysis of anonymized clinical data and blood routine results.

This study has received approval from the Ethics Committee of the Second Nanning People’s Hospital, granting a waiver for informed consent from participants because the research involves retrospective analysis of anonymized clinical data and blood routine results, with no direct contact or intervention with the patients. The study is observational in nature and aims to analyze the clinical data and blood routine results of women with advanced and younger maternal age IVF Dichorionic-Diamniotic twin pregnancies. There are no commercial interests involved, and the study poses no harm to participants.

Data analysis will be conducted using coded information, ensuring that no personal details (such as contact information, addresses, etc.) of the participants are collected. All samples and data will be de-identified to fully protect the privacy rights of the participants. Furthermore, the data used in this study will be strictly for research purposes and will not be used for any other purposes. The publication of research results will not disclose any personal identities of the participants.

This study will comply with relevant laws and regulations, including the Declaration of Helsinki. The researchers collectively assume responsibility for maintaining confidentiality, ensuring the security and privacy of participant information throughout the study.

Diagnostic Criteria

Discordant twin growth:Estimate the weight of one twin to be less than the third percentile for gestational age; or one twin meets at least two of the following three conditions: (1) estimated weight of one twin < 10th percentile; (2) difference in estimated weight between the two fetuses ≥ 25%; (3) pulsatility index of the smaller fetus’s umbilical artery > 95th percentile.¹²

Additionally, clarity regarding the assessment of “discordant twin growth” is warranted; it was assessed based on birth weight.

Statistical Analysis

Statistical analysis was performed using SPSS 29.0 software (IBM Corp., Armonk, NY, USA). Propensity score matching (PSM) was conducted based on maternal BMI, pregnancies, age at menarche.The nearest neighbor matching method was applied with a 1:1 ratio and a matching tolerance 0.02.Prior to PSM, there were 47 cases in the advanced maternal age group and 94 in the younger maternal age group. Following PSM, a total of 84 cases were included in the analysis, with 42 in the advanced age group and 42 in the younger maternal age group. Data conforming to a normal distribution or approximately normal distribution were expressed as mean ± standard deviation (), and comparisons between groups were made using t-tests, with P < 0.05 indicating statistical significance. Count data were expressed as rates (%), analyzed using the χ2 test, and Fisher’s exact test was applied when expected counts were <5, with P < 0.05 indicating statistical significance.

Results

Comparison of General Information

Prior to PSM, the advanced maternal age group had significantly higher age and pregnancies compared to the younger maternal age group (P<0.05), while BMI and age at menarche showed no significant differences (P>0.05). Following PSM, the advanced maternal age group continued to have a significantly higher mean age compared to the younger maternal age group (P<0.05), while BMI, pregnancies, and age at menarche showed no significant differences (P>0.05) (Table 1).

Table 1 Comparison of General Data Between the Two Groups of Pregnant Women Before and After Matching () M(P25,P75)

Comparison of Hemoglobin Levels and Pregnancy Complications

Prior to PSM, the incidence of placental abruption was higher in the advanced maternal age group compared to the younger maternal age group (P<0.05). No significant differences in hemoglobin levels during early and late pregnancy, as well as in GDM, HDP, ICP, and placenta previa (P>0.05). Following PSM, no significant differences were observed in hemoglobin levels, GDM, HDP, ICP, placenta previa, and placental abruption (P>0.05) (Table 2).

Table 2 Comparison of HB and Pregnancy Complications Between the Two Groups of Pregnant Women Before and After Matching (), (n)%

Comparison of Pregnancy Outcomes

No cases of postpartum hemorrhage occurred in either group.Prior to PSM, discordant twin growth was significantly higher in the advanced maternal age group compared to the younger maternal age group (P<0.05); however, differences in fetal growth restriction, LBW, PTB, PROM, and intraoperative blood loss were not statistically significant (P>0.05). Following PSM, discordant twin growth and intraoperative blood loss were significantly higher in the advanced maternal age group compared to the younger maternal age group (P<0.05), while differences in fetal growth restriction, LBW, PTB, and PROM were not statistically significant (P>0.05) (Table 3).

Table 3 Comparison of Pregnancy Outcomes Between the Two Groups of Pregnant Women Before and After Matching M(P25,P75), (n)%

Discussion

The results indicate that advanced maternal age nulliparous women face significantly higher rates of discordant twin growth and intraoperative blood loss compared to younger maternal age primiparas, suggesting that they may encounter greater risks of fetal growth discordance and bleeding in IVF twin pregnancies. However, no significant differences were observed between the two groups regarding other pregnancy outcomes such as PTB, LBW, placenta previa, placental abruption, GDM, HDP, and ICP. This finding emphasizes the importance of individualized and close monitoring for nulliparous women at advanced maternal age to address their unique risk factors and ensure favorable outcomes in IVF-conceived dichorionic-diamniotic twin pregnancies.

Principal Findings of This Study

Comparison of Pregnancy Complications

We found no significant differences between the two groups in terms of hemoglobin (HB) levels during early and late pregnancy, preterm birth, low birth weight, placenta previa, placental abruption, gestational diabetes mellitus (GDM), hypertensive disorders of pregnancy (HDP), and intrahepatic cholestasis of pregnancy (ICP) (P>0.05). The null finding may reflect rigorous glycemic/blood pressure control in AMA women under close prenatal surveillance. The overall prevalence of placenta previa was (4–5)/1000 deliveries, although there are regional variations globally, and the reasons for these discrepancies remain unclear.¹³ Some studies indicate that advanced maternal age is a risk factor for developing placenta previa.¹⁴ One study showed that the prevalence of placenta previa among twin pregnancies is 40% higher than that among singleton pregnancies (3.9/1000 vs 2.8/1000).¹⁵ Our study did not find a higher incidence of placenta previa in the high-age group, which may be attributed to the limitations of our sample size; future research could consider increasing the sample size in order to further investigate this. Regarding placental abruption, assisted reproductive technology (ART) may increase its incidence.^16,17 A retrospective study in China found that the risk of placental abruption increases with maternal age.¹⁸ In our study, the initial data showed a tendency for a higher incidence of placental abruption in the high-age group compared to the younger maternal age group; however, this difference became insignificant after propensity score matching (PSM), so the differences between the two groups were not significant. This may be due to the reduced sample size after PSM, which did not yield positive results. Nonetheless, we should remain vigilant about the incidence of placental abruption in the high-age population and enhance monitoring during pregnancy. Although BMI significantly impacts pregnancy outcomes among women aged 30–38 years, its effect is minimal in younger or older women.¹⁹ This aligns with our findings, suggesting that maternal age may have a limited effect on certain pregnancy outcomes. Regardless of the conception method, twin pregnancies increase morbidity and mortality for both mothers and infants; therefore, couples should be counseled about the iatrogenic risks associated with double embryo transfer. However, couples expecting twins can be informed that ART does not significantly worsen pregnancy outcomes compared to naturally conceived twin pregnancies.²⁰ Our study further supports this notion, as we found that advanced maternal age nulliparous women undergoing ART had similar pregnancy outcomes to younger maternal age nulliparous women. Compared to younger women, older women had significantly higher incidences of gestational diabetes, cesarean delivery, and fetal growth discordance in twin pregnancies, while the incidence of preeclampsia was not influenced by maternal age.²¹ The advanced maternal age nulliparous women in our study also exhibited higher fetal growth discordance, but no significant differences were observed regarding GDM, HDP, or other complications. The incidence of cesarean delivery and hypertensive disorders was significantly higher in women with twin pregnancies aged over 35, increasing with maternal age, yet the incidence of neonatal complications did not rise.²² Literature suggests that when the technique for vaginal delivery in twin pregnancies is not well mastered based on training and experience, cesarean delivery is a more appropriate choice.²³ We opted for cesarean delivery due to the value of IVF-conceived fetuses, as mothers and their families preferred this method.

Comparison of Pregnancy Outcomes

The results show that advanced maternal age nulliparous women exhibited significantly higher rates of discordant twin growth and intraoperative blood loss compared to younger maternal age nulliparous women (P<0.05). However, differences in fetal growth restriction, LBW, PTB, and PROM were not statistically significant (P>0.05). This suggests that maternal age may have a limited influence on certain pregnancy outcomes. Our findings suggest that, with appropriate monitoring during pregnancy, nulliparous women at advanced maternal age can achieve outcomes comparable to those of their younger counterparts. It is crucial to increase monitoring of fetal growth during pregnancy. A prospective cohort study reported that if singleton fetal growth standards are used, nearly 40% of dichorionic twins would be classified as small for gestational age near term.²⁴ Literature indicates that singleton fetal growth curves are the best indicators for adverse outcomes in twin pregnancies and should be used for assessing fetal growth abnormalities in twin gestations.²⁵ However, proponents of twin-specific growth curves argue that using singleton growth standards may lead to overdiagnosis of growth abnormalities, resulting in unnecessary maternal anxiety and prenatal examinations, potentially leading to preterm delivery without improving neonatal outcomes.^26,27 Therefore, it is essential to select appropriate fetal growth assessment standards in twin pregnancies to avoid excessive intervention and unnecessary anxiety. Some literature suggests that many growth abnormalities in twins can be detected between 20–24 weeks, and if no abnormalities are found during this period, repeated ultrasound examinations may not be necessary.²⁸ However, some authorities recommend routine ultrasound examinations every 2–4 weeks,²⁹ which is also our practice. The complication rates and mortality of twin pregnancies are higher than those of singleton pregnancies, primarily due to fetal growth restriction and preterm birth, making fetal growth assessment particularly important.^30–32 Our study also found that advanced maternal age nulliparas are more likely to experience fetal growth discordance in twin pregnancies. Thus, close monitoring and individualized management are critical for these high-risk pregnancies. Emerging evidence suggests that the association between mild discordant twin growth and abnormal placental pathology primarily manifests through its impact on small-for-gestational-age (SGA) status in the smaller twin.³³ The increased intraoperative blood loss observed in the AMA group compared to YMA counterparts may correlate with discordant twin growth patterns. Existing literature demonstrates that growth discordance, particularly when complicated by fetal growth restriction (FGR), is associated with elevated postpartum hemorrhage risk in twin pregnancies undergoing cesarean delivery, with this association being more pronounced in dichorionic twins.³⁴ Advanced maternal age and nulliparity can both lead to maternal vascular malperfusion (MVM), and the level of discordant twin growth in twins is significantly associated with MVM lesions.³³ Deterioration of utero-placental perfusion is highly correlated with the differences in perfusion, which is closely related to discordant twin growth twins.³⁵ While our data did not distinguish between fresh or frozen embryo transfers – a potential confounding factor in pregnancy outcomes – current evidence suggests no significant differences in perinatal outcomes between these transfer modalities.³⁶

Conclusions

Clinical Implications of the Study

In conclusion, women of AMA who undergo IVF experience a higher risk of certain complications in DCDA twins, such as discordant twin growth and intraoperative bleeding. However, when provided with adequate prenatal care, their pregnancy outcomes are comparable to those of younger primiparous women. This finding offers reassurance to older women considering IVF for twin pregnancies, suggesting that with appropriate medical interventions and careful monitoring—including enhanced fetal growth surveillance, such as serial ultrasounds at 2–4-week intervals or ideally biweekly monitoring schedules—the potential risks can be effectively managed.

Limitations of the Study

As a retrospective single-center study, our findings are constrained by a limited sample size (post-PSM n=84), which may be underpowered to detect differences in rare outcomes like placental abruption (observed in 5 cases, pre-PSM) and placenta previa. This limitation inherently restricts the generalizability of our findings. Furthermore, while we accounted for matching variables such as BMI, menarche age, and gravidity, we did not comprehensively address potential confounding factors, including socioeconomic status, lifestyle, and genetic background. Unmeasured confounders, such as socioeconomic status and embryo quality (eg, blastocyst vs cleavage-stage transfer), could influence outcomes but were unavailable for analysis.

Prospects

To enhance the reliability and generalizability of our results, future research should adopt a multicenter, large-sample, prospective design. Moreover, it is essential to investigate specific risk factors and develop intervention strategies tailored specifically for primiparous women of advanced maternal age undergoing IVF for twin pregnancies, with the aim of optimizing prenatal management protocols. By integrating advanced monitoring technologies and personalized medical interventions, there is significant potential to substantially improve pregnancy outcomes.

In addition to the aforementioned considerations, it is crucial for future research to systematically evaluate the impact of socioeconomic factors and the type of embryo transfer (fresh vs frozen) on pregnancy outcomes. By including these variables in the study design, we can better control for potential confounding effects and improve the robustness of our findings. This comprehensive approach will not only enhance the reliability of our results but also provide deeper insights into the multifaceted nature of factors influencing twin pregnancies in primiparous women of advanced maternal age undergoing IVF.