Understanding GDM Screening in Multiple Pregnancies

Gestational diabetes mellitus (GDM) presents distinct challenges in multiple pregnancies, where physiological adaptations are more pronounced and clinical decision-making carries higher stakes. Because twin and triplet gestations are increasingly common due to assisted reproductive technologies and advanced maternal age, clinicians must be well-versed in the nuances of screening, diagnosis, and management for these higher-risk patients. This article provides a comprehensive overview of GDM screening in multiple pregnancies, addressing unique pathophysiological, methodological, and management considerations.

Why Multiple Pregnancies Require Special Attention

Multiple pregnancies involve greater placental mass, elevated levels of human placental lactogen, progesterone, and other diabetogenic hormones, which collectively increase insulin resistance. Compared with singletons, women carrying twins or triplets exhibit a more rapid rise in blood glucose levels as gestation progresses. Studies have reported GDM prevalence rates 2–3 times higher in multiple gestations, depending on the diagnostic criteria used. This heightened risk means that a negative screening result early in pregnancy does not guarantee normoglycemia later, and many guidelines recommend intensified surveillance.

Beyond glucose metabolism, multiple pregnancies are associated with higher rates of preterm delivery, preeclampsia, and fetal growth abnormalities. GDM superimposed on these risks can further complicate outcomes, increasing the likelihood of macrosomia (especially discordant growth), neonatal hypoglycemia, and respiratory distress. Accurate and timely screening is therefore critical to initiate interventions that can mitigate these adverse effects.

Pathophysiology of GDM in Multiple Gestations

Insulin Resistance and Placental Hormones

The placenta produces hormones that antagonize insulin action, including human placental lactogen (hPL), growth hormone variant, and tumor necrosis factor-alpha. In multiple pregnancies, the larger placental mass leads to higher circulating levels of these hormones, shifting the maternal metabolic profile toward greater insulin resistance. This effect is dose-dependent: triplet pregnancies typically show more severe insulin resistance than twin pregnancies, and both are more insulin-resistant than singletons at the same gestational age.

Pancreatic beta-cell compensation must keep pace with escalating demand. In women with insufficient beta-cell reserve, glucose intolerance develops by the late second or early third trimester. The accelerated decline in insulin sensitivity observed in multiples often leads to an earlier onset of hyperglycemia compared to singleton pregnancies. Some researchers have proposed screening as early as 16–20 weeks for women with known risk factors such as obesity, polycystic ovary syndrome, or a history of GDM.

Hemodilution and Glucose Distribution

Multiple pregnancies are characterized by a greater expansion of plasma volume (up to 50–60% in twins versus 40–50% in singletons). This hemodilution can lower fasting glucose concentrations, potentially masking GDM if only fasting values are considered. Conversely, the larger fetal placental unit may consume more glucose, creating a counter-balancing effect. These competing factors contribute to variability in glucose profiles and underscore the need for comprehensive oral glucose tolerance testing (OGTT) rather than reliance on fasting glucose alone.

Screening Timing and Methods

Current Guidelines and Variability

The two main international protocols for GDM screening are the two-step approach favored by the American College of Obstetricians and Gynecologists (ACOG) and the one-step approach endorsed by the International Association of Diabetes and Pregnancy Study Groups (IADPSG). ACOG recommends a 50-gram glucose challenge test (GCT) at 24–28 weeks, followed by a 100-gram 3-hour OGTT for those with a positive screen. The IADPSG one-step method uses a 75-gram 2-hour OGTT with lower diagnostic thresholds.

Neither set of guidelines was developed specifically for twin or higher-order multiple pregnancies. However, expert opinion increasingly advocates for earlier screening in multiples. The Society for Maternal-Fetal Medicine (SMFM) has suggested that clinicians consider screening twin pregnancies at 24–28 weeks with a 50-gram GCT, but also note that a 75-gram OGTT may be more appropriate due to the higher prevalence of GDM. For triplet pregnancies, data are limited, and many practitioners perform both early and late screening.

Early screening (before 20 weeks) is not universally recommended because the physiological insulin resistance of pregnancy has not yet peaked, and false negatives are common. However, women with strong clinical risk factors—such as a body mass index greater than 30, prior GDM, or a first-degree relative with diabetes—may benefit from a baseline 75-gram OGTT as early as the first prenatal visit. If results are normal, repeat screening at 24–28 weeks is still advised.

Interpreting OGTT Results in Multiples

Whether to adjust diagnostic thresholds for multiple pregnancies remains controversial. Some studies have suggested that using the standard IADPSG criteria in twin pregnancies identifies more women with GDM but does not necessarily improve outcomes. A 2022 systematic review in BJOG: An International Journal of Obstetrics & Gynaecology found that the risk of adverse outcomes (e.g., large for gestational age, preeclampsia) was similar for twin pregnancies with GDM diagnosed by either one-step or two-step methods. At present, most guidelines do not recommend separate thresholds for multiples but do emphasize that the diagnosis should be interpreted in the context of the patient’s overall risk profile and clinical presentation.

Special Considerations in Screening

Fetal Growth and Discordance

GDM in twin pregnancies increases the risk of inter-twin growth discordance (defined as a weight difference of ≥20%). The larger twin may become macrosomic while the smaller twin remains appropriate or even growth-restricted, complicating management. Regular ultrasound surveillance every 4–6 weeks after diagnosis is standard, with attention to estimated fetal weight, amniotic fluid volume, and umbilical artery Doppler waveforms. If discordance becomes severe, earlier delivery may be considered.

Preterm Birth and Timing of Screening

Multiple pregnancies have a median gestational age at delivery significantly earlier than singletons: around 36 weeks for twins and 32–34 weeks for triplets. This truncated window means that if screening is deferred to 28 weeks, some women may deliver before the diagnosis is made. Some experts recommend that twin pregnancies undergo a 50-gram GCT at 24–26 weeks, with immediate follow-up OGTT if positive, and a repeat screen at 30–32 weeks for those who remain undiagnosed. For triplets, many clinicians perform a 75-gram OGTT at 24–26 weeks without a preliminary glucose challenge test.

Maternal Weight Gain and Glycemic Targets

Weight gain recommendations for women with GDM and multiple pregnancies are not well-established. The Institute of Medicine provides separate weight gain guidelines for twin pregnancies (based on prepregnancy BMI) but does not offer adjusted targets for those with GDM. Generally, tighter glycemic control is recommended to limit fetal overgrowth, but not so strict that maternal ketosis develops. A dietitian experienced with both GDM and multiples should tailor calorie distribution to maintain euglycemia while supporting adequate nutrition for all fetuses.

Management Strategies for GDM in Multiples

Lifestyle and Pharmacotherapy

Initial management follows the same principles as for singletons: medical nutrition therapy, carbohydrate counting, and moderate physical activity. However, women carrying twins may find exercise more challenging due to ligamentous laxity, pelvic discomfort, and earlier fatigue. Low-impact activities such as walking, stationary cycling, or water aerobics are preferred.

Approximately 40–60% of women with GDM and twins require pharmacotherapy, compared with 20–30% for singleton pregnancies. Insulin remains the first-line agent because it does not cross the placenta in significant amounts and allows precise dose titration. Rapid-acting analogues (lispro, aspart) are commonly used for prandial control, while NPH or detemir provide basal coverage. Oral agents such as metformin and glyburide have been studied in twin pregnancies, but data are limited. A 2020 cohort study in Diabetes Care found that metformin was associated with a higher rate of treatment failure in twin compared with singleton GDM. Glyburide has also been linked to an increased risk of neonatal hypoglycemia and macrosomia in some studies, making it a less preferred option in multiples.

Frequency of Monitoring

Women with GDM in multiple pregnancies should self-monitor blood glucose levels at least four times daily (fasting and one hour postprandial). Fasting targets ≤95 mg/dL and one-hour postprandial ≤140 mg/dL are typical, though some clinicians use tighter targets (≤90 mg/dL fasting) given the increased risk of macrosomia. Continuous glucose monitoring may be beneficial for women with unstable glucose patterns or difficulty achieving targets.

Antenatal visits every 1–2 weeks are standard, with more frequent fetal surveillance (nonstress tests or biophysical profiles) starting at 32–34 weeks. Ultrasound for growth and amniotic fluid assessment is performed every 4 weeks. If glycemic control is poor or fetal complications arise (e.g., polyhydramnios, growth discordance), hospitalization for intensive monitoring may be necessary.

Delivery Timing and Mode

The goal is to achieve delivery between 38+0 and 39+6 weeks for uncomplicated twins with well-controlled GDM. For triplets or higher-order multiples, delivery is typically planned earlier (32–34 weeks) based on obstetric indications rather than glucose control alone. Induction of labor or scheduled cesarean delivery is common in multiples due to higher rates of malpresentation and the complexity of intrapartum management. Continuous maternal glucose monitoring during labor is recommended, with insulin or dextrose infusions adjusted to maintain maternal glucose between 100–140 mg/dL, thereby reducing the risk of neonatal hypoglycemia.

Postpartum Considerations

Glucose Testing and Long-Term Risk

All women who had GDM should undergo a 75-gram 2-hour OGTT at 4–12 weeks postpartum to screen for type 2 diabetes or prediabetes. The presence of a multiple pregnancy does not alter this recommendation, but the higher metabolic stress of multiples may accelerate progression: women with GDM and twins have a 30–50% higher 5-year risk of developing type 2 diabetes compared with those with singleton GDM, according to longitudinal data from the Nurses' Health Study. Lifestyle modification and annual diabetes screening are essential.

Breastfeeding and Contraception

Breastfeeding improves maternal glucose metabolism and reduces the risk of postpartum diabetes progression. However, women with multiples often face logistical barriers to exclusive breastfeeding. Lactation support and pumped feeding strategies should be offered proactively. For contraception, progestin-only methods (e.g., IUDs, implants) are preferred in women with a history of GDM because combined oral contraceptives can worsen insulin resistance. Long-acting reversible contraception is ideal for spacing pregnancies and reducing the metabolic recurrence risk.

Future Directions and Research Gaps

Despite the growing prevalence of multiple pregnancies, robust evidence specifically addressing GDM screening in twins and triplets remains sparse. Key unanswered questions include:

  • Should diagnostic thresholds be adjusted for multiples? While some authors propose lowering the fasting glucose cut-off for twins, prospective trials are lacking.
  • What is the optimal early screening protocol? The utility of first-trimester HbA1c or random glucose in predicting GDM in multiples is not well established.
  • What are the long-term metabolic consequences for offspring? Twin pregnancies complicated by GDM may program the offspring for future obesity and diabetes, but long-term follow-up studies are few.
  • How should intrapartum glycemic targets be individualized? Current guidelines extrapolate from singleton data, but the larger fetal mass in multiples may require different thresholds.

Ongoing multicenter registries, such as the National Institute of Child Health and Human Development's Maternal-Fetal Medicine Units Network, are beginning to address these gaps. Clinicians are encouraged to contribute to research efforts and to counsel patients about the limitations of current knowledge.

Conclusion

GDM screening in multiple pregnancies demands a proactive, individualized approach. The combination of enhanced insulin resistance, truncated gestational windows, and heightened fetal risks necessitates earlier assessment, careful selection of screening methods, and close surveillance. While many management strategies align with singleton GDM care, adjustments in timing, diagnostic interpretation, and pharmacotherapy are often warranted. By staying current with evolving guidelines and leveraging multidisciplinary expertise—including maternal-fetal medicine specialists, dietitians, and neonatologists—healthcare providers can improve outcomes for both mother and babies. Continued research into optimal screening protocols and therapeutic targets will further refine care for this growing population.

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