Prenatal detection of fetal macrosomia was 145/268 (54.1%). A third-trimester ultrasound scan (USS) was conducted on 217/268 (80.9%) mothers, while a higher number of mothers, 255/268 (95.1%), received SFH monitoring. The identification of macrosomia was either by SFH monitoring only 46/145 (31.7%), ultrasound scan assessment only 48/145 (33.1%), or confirmed by both methods 51/145 (35.2%). USS assessment had a higher macrosomia detection rate of 99/217 (45.6%) compared to SFH monitoring 97/255 (38%) (p < 0.001).

Most pregnancies affected by macrosomia, 152/268 (56%), experienced spontaneous labor as shown in Figure 2. Macrosomia was undetected in 80/152 (52.6%) of mothers who went into spontaneous labor. Emergency caesarean (EMCS) was done for 87/138 (63.0%) of abdominal deliveries, compared to only 51/138 (37%) elective CS deliveries. An elective caesarean section was done for 51/268 (18.7%) of mothers, and 65/268 (24.3%) mothers underwent induction of labor (IOL). A sizable number of IOLs performed 29/65 (44.6%) were eventually delivered via emergency caesarean section (EMCS). A comparative number of mothers had CS delivery, 138/268 (51.5%), contrasted to 130/268 (48.5%) who had vaginal deliveries. Most vaginal deliveries had undiagnosed macrosomia 75/130 (57.7%), while most abdominal deliveries had identified macrosomia pre-delivery 90/138 (65.2%). The risk of CS was particularly high for primiparous mothers, 45/78 (57.7%). The occurrence of labor in macrosomic fetuses was statistically significant (p < 0.001).

Figure 2.Fetal macrosomia and labor initiation.

Emergency caesarean (EMCS) was done for 87/138 (63.0%) compared to only 51/138 (37%) elective CS deliveries. Assisted delivery with forceps 5/268 (1.9%) and vacuum extraction 10/268 (3.7%) was reported. 12/15 (80%) of deliveries with assisted vaginal delivery were not detected prenatally. Vaginal episiotomy was performed in 28/130 (21.5%) of vaginal deliveries. The effect of identification of fetal macrosomia on the mode of delivery was statistically significant (p = 0.001).

Detection was influenced by maternal rather than fetal factors such as IGT/GDM (p = 0.02), high BMI (≥30, p = 0.01), previous CS (p = 0.027), previous macrosomia (p = 0.004), and EGA ≥ 40 weeks (p = 0.026).

Maternal complications occurred with 125 (46.6%) mothers, of which 68 (54.4%) were identified as macrosomic pregnancies, as shown in Table 1. Shoulder dystocia occurred equally between the detection groups. The most frequent complications were perineal trauma 77/268 (28.7%), prolonged labor 41/268 (15.3%), post-partum hemorrhage (PPH) 24/268 (8.9%), and shoulder dystocia 14/268 (5.2%). Perineal trauma included perineal tears 49/268 (18.3%) and episiotomy 28/268 (9.7%). None of the mothers experienced grade 3 or 4 (OASIS) perineal tears. The exclusion of perineal trauma in the analysis for maternal peripartum complications did not change the trend in maternal complications. The composite adverse maternal peripartum outcome occurred in 68/145 (46.9%) [Odds ratio 1.01, confidence interval (95% CI) 0.8 to 1.3] mothers with prenatally detected macrosomia versus 57/123 (46.3%) [OR 0.99, 95% CI 0.8 to 1.2] in the undetected group. The crude relative risk was 1.02 (95% CI 0.6 to 1.7).

Table 1.Maternal obstetric condition at delivery.

One stillbirth was observed. Most fetal complications were comparable between the detection groups, as shown in Table 2, although neonatal sepsis and NICU admission occurred more frequently with the detected group. There was no statistical difference noted for the occurrence of adverse neonatal outcomes across different gestational ages, although a tendency for increased frequency at full and late term was observed. Fetal complications were more common after 39 weeks. Early-term (<38 weeks) and extremely late pregnancies (>42 weeks) had low counts overall, making trends less clear.

Table 3 shows the trend in maternal and fetal complications by gestational age at delivery. Few deliveries occurred at early-term between 37⁺⁰ to 38⁺⁶ weeks, and tended towards slightly more infants with complications, which suggests that infants might be more vulnerable before full term. 39 weeks showed a high number of healthy mothers but a notable rise in fetal complications. Likely the most physiologically optimal time for delivery.

Table 2.Neonatal perinatal outcomes.

Table 3.Summary of trends in maternal vs fetal complications by gestational age (EGA).

Prenatal identification of macrosomia was made for 54.1% deliveries. SFH was more widely used (95.1% of mothers) compared to ultrasound (80.9%). Ultrasound had a higher detection rate, although both approaches—third-trimester USS examination and clinical SFH measurements—were not very effective at detecting macrosomia. A 2018 Cape Town-based study reported a USS sensitivity of 58.3% (CI: 36% - 82%) for detecting macrosomia, with a specificity of 96.5% (CI: 93% - 99%) [9]. The current study aligns with this trend, with a USS detection rate of 45.6% for macrosomia. Other studies have shown similar findings, designating USS as the gold standard for prenatal macrosomia detection. SFH monitoring detected macrosomia in 38% of cases. This finding is consistent with other studies where SFH has been reported to have a low detection rate of about 30% - 50% for macrosomia [10]. The poor detection using SFH is likely due to the measurement being affected by factors such as maternal body size, fetal position, amniotic fluid volume, and uterine abnormalities. Combining SFH with USS is expected to offer a more comprehensive approach to prenatal care. This aligns with findings from other studies, which suggest that using multiple methods improves overall detection rates. This current study found that the difference in detection rates between USS and SFH monitoring was statistically significant (p < 0.001), reinforcing the idea that USS is a superior method for prenatal detection of macrosomia.

4.1.1. Timing of Delivery

The prenatal detection of fetal macrosomia plays a significant role in determining the mode and timing of delivery. All deliveries for this study occurred after 37 weeks’ gestation, with many deliveries (84.3%) taking place at 39 - 41 weeks, which aligns with the typical pattern observed in other studies. Macrosomia was associated with post-term pregnancies (≥40 weeks), as 67% of births for this study occurred at or beyond 40 weeks. The higher rate of macrosomia among post-term deliveries was consistent with other literature, which has reported that infants born after 40 weeks of gestation had an increased risk of macrosomia, likely due to continued fetal growth and increased placental transfer of nutrients, especially with co-morbidities such as maternal obesity or diabetes [8]. The tendency for macrosomic infants to be delivered post-term is particularly significant in obstetric practice, as post-term pregnancies are known to carry higher risks, both for the baby (e.g., shoulder dystocia, birth trauma, and caesarean delivery) and for the mother (e.g., raised risk of pre-eclampsia and labor complications). The absence of macrosomic births before 37 weeks supports the understanding that macrosomia is primarily a condition of term or post-term pregnancies. Preterm macrosomia is rare, and when it does occur, it is often associated with underlying medical conditions, such as maternal diabetes or other metabolic disorders that may trigger early excessive fetal growth.

The timing of delivery for macrosomic infants is a critical area of obstetric management. The decision to induce labor or to opt for elective caesarean delivery, especially in post-term pregnancies, is an area of ongoing debate. Some studies have suggested that elective IOL at 39 weeks for suspected macrosomia can reduce the risks of complications like shoulder dystocia without increasing caesarean section rates. However, others have highlighted that waiting for spontaneous labor, particularly for mothers without other risk factors such as gestational diabetes, might be appropriate, as macrosomia alone is not always an indicator of the need for early delivery. The data from the current study showed that most deliveries of macrosomic infants (84.3%) occurred in the 39 - 41 weeks range, with 56% experiencing spontaneous labor, likely indicating that the detected pregnancies were managed expectantly. Most deliveries in this study population were performed post-dates, and this also raises important questions about the pregnancy management and whether earlier interventions, like induction or planned caesarean delivery, could have reduced the risks associated with post-term macrosomia.

4.1.2. Mode of Delivery

The optimal mode of delivery for suspected macrosomic pregnancies remains a controversial topic, with no clear consensus regarding best practice. The 2021 National Institute for Health and Care Excellence (NICE) guidelines recommend a shared decision-making approach, whereby women and their partners are counseled on the potential benefits and risks of the available management options, including elective lower-segment caesarean section (ELCS), induction of labor (IOL), and expectant management [11][12]. While the Royal College of Obstetricians and Gynecologists (RCOG) recommends offering ELCS to women with diabetes when the estimated fetal weight (EFW) is ≥4.5 kg because of the increased risk of shoulder dystocia and birth trauma, there is currently no consensus regarding the EFW threshold at which ELCS should be recommended for non-diabetic women [13]. Consequently, management in this population remains individualized, considering clinical factors, maternal preferences, and the limitations of fetal weight estimation. For the current study, the incidence of vaginal episiotomy (21.5%), instrumental delivery (11.5%), and CS (51.5%) was high. A sizable number (11.5%) of vaginal deliveries involved assisted delivery methods (forceps or vacuum extraction), with a majority (80%) of those cases having undetected macrosomia. The high incidence of CS for this current study was consistent with global reports from several researchers in diverse ethnic groups.

Of the 268 deliveries, 51.5% were caesarean deliveries, and 65.2% of CS had identified macrosomia before delivery. This study observed that 18.7% of mothers underwent an ELCS in the context of macrosomia. Elective caesareans for macrosomia are often performed based on the results of ultrasound and clinical assessments, with a preference for caesarean delivery in cases where the estimated fetal weight (EFW) exceeded 4500 g. Scheduled ELCS are generally recommended for presumed birth weight > 4000 g in diabetic mothers and a variable range of 4000 g to >4500 g, depending on the setting for women without diabetes. Nevertheless, this strategy remains contentious because there are no RCTs providing conclusive evidence for non-diabetics. Other researchers have cautioned on the importance of balancing the risks of CS with the benefits of avoiding birth injuries. Thus, while ELCS are common, the optimal approach remains debated. For this current study, macrosomia when detected prenatally had an increased tendency to be delivered via CS.

Out of the total study population of 268 mothers, 65 (24.3%) underwent IOL. Of these, 49.2% (32/65) had macrosomia detected before IOL, while the remaining 51.8% (33/65) were not identified predelivery. Inducing labor at 40 weeks of gestation may be driven by concerns for challenges, including shoulder dystocia, prolonged labor, and birth trauma. In this study, the induction at full term was consistent with international guidelines, which typically recommend waiting until 39 weeks unless there are specific maternal or fetal indications. Researchers have suggested that early IOL for suspected macrosomia could result in a reduced likelihood of CS. For this study, 44.6% of induced labors resulted in CS.

Most mothers (91.8%) received routine obstetric care during their hospitalization. Women with macrosomic pregnancies are at higher risk of pregnancy complications such as hypertensive disorders and eclampsia [14], especially if macrosomia was not detected early and when these conditions are not diagnosed or managed appropriately during pregnancy. For the current study, maternal complications were generally similar between the detection groups. Prolonged labor and postpartum hemorrhage were more frequent in the detected group, with 61% of prolonged labor cases and 62.5% of PPH. Perineal tears occurred more often (55.8%) among the undetected group. The finding that perineal trauma occurred frequently with macrosomia aligns with existing literature. Remarkably, for the current study population, no OASIS injury was noted for any of the deliveries.

Although shoulder dystocia occurred equally between detection groups, fewer fetal complications 4/7 (57.1%) were observed among those with detected macrosomia compared to undetected pregnancies 6/7 (85.7%). Macrosomic infants born after 39 weeks had an increased risk of birth-related injuries. The numbers for this study were, however, too small to draw strong conclusions. The big baby trial showed similar findings of a significant reduction in shoulder dystocia in their per-protocol analysis for pregnancies with IOL between 38⁺⁰ weeks’ and 38⁺⁴ weeks’ gestation compared with deliveries after 38⁺⁴ weeks’ gestation. The big baby trial, however, reported that, in their intention-to-treat analysis, the incidence of shoulder dystocia did not differ clinically between trial groups [14].

Hypoglycemia was observed in 35.1% infants, with 20% of NICU admissions attributed to hypoglycemia. The incidence of hypoglycemia was highest among babies whose mothers had IGT/GDM 13/22 (59.1%). These infants required glucose monitoring and guaranteed feeds to stabilize blood sugar levels. While most of the cases were managed with non-invasive approaches, the frequent monitoring and additional feeding support highlighted the metabolic vulnerabilities of these infants.

Deliveries at 41 - 43 weeks showed an increased trend of complications for both mother and infant. This suggests that post-term pregnancies are at increased risk, especially for fetal complications. The findings of this study correlate with the recent big baby trial, which sought to guide clinicians on the timing and mode of delivery for pregnancies affected by macrosomia. The researchers reported a significant reduction in shoulder dystocia when macrosomic pregnancies were induced between 38⁺⁰ weeks’ gestation and 38⁺⁴ weeks’ gestation compared to the standard care group [15]. Early delivery by 40 weeks of gestation is expected to lessen the risk of peripartum complications compared to expectant management for pregnancies affected by macrosomia. Early term delivery before 39 weeks was, however, not shown to be of benefit in this study.