Introduction

Contemporary healthcare has made pregnancy and childbirth relatively safe for women living in Iran. The maternal mortality rate in Iran has decreased from 123 in 1995 to 17 in 2017 per 100,000 live births. Maternal mortality in Iran is lower than the average for its region1. Improvements in outcomes have been influenced by various factors, such as elevated hygiene and sanitation standards and better nutrition; however, most crucially, the growth of maternity care2. Nonetheless, one of the primary concerns not only for those living in Iran but for people globally is obesity. Recent studies indicate that obesity is likely the most significant among the four major global risk factors that meet the criteria set by the government for determining health priorities3. Obesity is an escalating public health issue worldwide, with its prevalence rising among women of childbearing age4. The prevalence of overweight and obesity shows considerable variation globally, with the highest rates among women found in the Pacific island countries, the Caribbean, and the Middle East. It is estimated that nearly 39 million pregnancies globally each year are complicated by maternal obesity5.

As maternal obesity becomes more prevalent in our societies, it is inevitable for all maternity care professionals to encounter its specific challenges during pregnancy and childbirth6. Therefore, maternal body weight significantly influences the likelihood of issues such as infertility, miscarriages, fetal defects, birth complications, and various long-term negative consequences for both mothers and their children7, making targeted foundational research essential. In this study, we aim to examine the association between pre-pregnancy high maternal weight and maternal and neonatal complications.

Methods

This retrospective cohort study examined data from mothers who delivered at Khaleej-e-Fars Hospital in Bandar Abbas, Iran, a tertiary medical facility, from January 2022 to January 2023. Details of all qualified individuals were obtained from the national electronic health system, where filling out the sections concerning demographic details, medical histories, and data about the current pregnancy and delivery is obligatory, ensuring no information is overlooked. Consequently, although this study was retrospective, no information has been overlooked. Individuals with a BMI below 18.5 kg/m² and those with multiple gestations were not included. Given that multiple gestations are significant confounders; we attempt to exclude them from the eligibility criteria. Consequently, 2,930 mothers were categorized into three groups: (1) Normal weight (BMI: 18.5–24.9 kg/m²); (2) Overweight (BMI: 25.0–29.9 kg/m²); and (3) Obese (BMI ≥ 30.0 kg/m²). A midwife typically measures height and weight during the initial antenatal appointment, usually before 12 weeks of pregnancy. BMI was determined by applying the formula weight (kg)/height (m²).

The outcome measures consisted of maternal or neonatal complications based on when they occur during the pregnancy, including gestational diabetes, pre-eclampsia, intrauterine growth retardation (IUGR), large for gestational age (LGA), intrauterine fetal death (IUFD), placental abruption, presence of meconium in amniotic fluid, fetal distress, induced labor, type of delivery, shoulder dystocia, birth injury, need for episiotomy, high-grade perineal and vaginal lacerations, maternal intensive care unit (ICU) admission, low Apgar score (under ‘7’ at one and five minutes), need for neonatal resuscitation, and neonatal intensive care unit (NICU) admission.

Factors such as age, educational level, place of residency, parity, gestational age, and maternal health conditions like cardiovascular disease, thyroid disease, anemia, chronic hypertension, a history of abortion, a history of infertility, a history of IUFD, and a history of neonatal death were considered potential confounding variables and included as covariates in the adjusted analyses.

Patient characteristics were provided as frequencies (percentages). Categorical variables were analyzed using the chi-square test in SPSS (version 25.0, IBM Corp, Armonk, NY, United States). Binomial logistic regression models were utilized to determine odds ratios (ORs). The groups with overweight and obesity were compared with the normal BMI group (the reference population). A 95% confidence interval was generated for all odds ratios. The evaluation of the results followed a systematic procedure. A p-value < 0.05 was considered statistically significant.

Results

In the current study, out of 2,930 pregnant women, 819 (27.9%) were classified as overweight and 190 (6.5%) as obese. Table 1 displays the sociodemographic and obstetric characteristics of the pregnant women who participated in the study. The majority of overweight and obese women were aged between 19 and 34 years. Most of them held a high school diploma. In most instances, their gestational age ranged from 37 to 40 weeks. Most of them resided in rural areas and had given birth multiple times. The chi-square test revealed a significant difference between groups in terms of age, education level, and parity.

Table 1 Scio-Demographic and obstetrics characteristics of the participating pregnant women.
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Table 2 displays the maternal outcomes for pregnant women who are obese or overweight. The three groups showed significant differences regarding gestational diabetes, preeclampsia, labor onset, delivery type, necessity for episiotomy, and maternal ICU admission. Mothers who are overweight and obese exhibited increased occurrences of gestational diabetes, preeclampsia, induced labor, operative deliveries, cesarean deliveries, and admissions to the ICU. The frequency of episiotomy was lower in mothers who were overweight and obese.

Table 2 Maternal outcomes among obese and overweight pregnant women.
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Table 3 evaluates the three groups regarding neonatal outcome measures, revealing that instances of LGA were more frequent among overweight and obese mothers. The remaining neonatal outcome measures displayed no statistical differences among the groups.

Table 3 Neonatal outcomes among obese and overweight pregnant women.
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In the following step, binomial logistic regression was employed, and significant socio-demographic, obstetric, maternal, and neonatal variables (those with P value ≤ 0.05) were included in the model for overweight and obese pregnant women in relation to normal weight, as displayed in Tables 4 and 5.

As indicated in Table 4, the risk of, preeclampsia (OR = 2.148, CI = 1.401–3.294, P < 0.001) and gestational diabetes (OR = 1.612, CI = 1.319–1.971, P < 0.001) was greater in overweight mothers than in mothers of normal weight.

The odds of normal vaginal delivery (OR = 0.583, CI = 0.417–0.817, P = 0.003) were notably reduced in overweight mothers compared to those with normal weight. Thus, with each rise in the overweight score while keeping all other variables constant, the odds of preeclampsia and gestational diabetes increased by 2.148 and 1.319, respectively, while normal vaginal delivery experienced a decrease of 0.583. Among the socio -demographic and obstetric variables, primary parity and chronic HTN were significant between the two groups.

Table 4 Binomial regression of Scio-demographic and obstetrics characteristics, maternal and neonatal outcome in overweight compared with normal weight pregnant women*.
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Table 5 illustrates varying risks of induced labor (OR = 2.046, CI = 1.208–3.466, P = 0.008), preeclampsia (OR = 3.079, CI = 1.673–5.664, P < 0.001), gestational diabetes (OR = 2.378, CI = 1.706–3.316, P < 0.001), normal vaginal delivery (OR = 0.438, CI = 0.231–0.828, P = 0.011), and maternal ICU admission (OR = 5.088, CI = 1.502–17.232, P = 0.009) in obese mothers compared to those of normal weight. Thus, for every rise in the obesity score while keeping all other variables unchanged, the odds of induced labor, preeclampsia, gestational diabetes, and maternal ICU admission increased by 2.046, 3.079, 2.378, and 5.088 respectively. Thus, with each rise in the obesity score while keeping all other variables unchanged, the likelihood of a normal vaginal delivery diminished by 0.438. Among the socio -demographic and obstetric variables, primary education and chronic hypertension were significant between the two groups.

Table 5 Binomial regression of Scio-demographic and obstetrics characteristics, maternal and neonatal outcome in obese compared with normal weight pregnant women*.
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Discussion

The prevalence of overweight and obesity among our population was 27.9% and 6.5%, respectively, indicating that 34.4% of expectant mothers were not at a healthy weight. A comparison of the three groups of mothers (normal weight, overweight, and obese) revealed notable differences in gestational diabetes, preeclampsia, labor onset, delivery method, need for episiotomy, and maternal ICU admissions.

Overweight mothers faced a higher risk of preeclampsia and gestational diabetes compared to mothers with normal weight. The instances of normal vaginal delivery were significantly lower in overweight mothers than in those of normal weight. As the overweight score increased, the rates of preeclampsia and gestational diabetes increased by 2.148 and 1.319, respectively, while normal vaginal deliveries decreased by 0.583. The likelihood of induced labor, preeclampsia, gestational diabetes, vaginal delivery, and maternal ICU admission was significantly different in obese mothers compared to those with normal weight. With each increase in the obesity score, the rates of induced labor, preeclampsia, gestational diabetes, and maternal ICU admission rose by 2.046, 3.079, 2.378, and 5.088, respectively. As the obesity score increased, the chances of a normal vaginal delivery decreased by 0.438.

Worldwide, the rates of overweight and obesity have been consistently rising, increasing from 9.8% in 2006 to 13.2% in 2016, and are now approaching epidemic levels across the globe8,9. There is insufficient definitive global data showing the shifts in trends of maternal overweight and obesity. Up until now, no research has examined the shifting trends in global prevalence. Various studies have reported the prevalence of maternal overweight and obesity; however, the majority of these studies, including ours, have been conducted in small populations. The absence of accurate and reliable statistics on maternity obesity rates prevents us from comparing the incidence of obesity in our population to determine if it exceeds or falls below the standard.

The links between elevated maternal BMI and pregnancy-related conditions have shown that the likelihood of gestational hypertension and pre-eclampsia rises consistently with higher BMI10, aligning with our findings. Our research additionally revealed that, in addition to increased pre-eclampsia risks for obese women, being overweight was significantly linked to this condition as well, albeit to a lesser extent. A meta-analysis examining the link between maternal BMI and the likelihood of pre-eclampsia indicated that the risk increased twofold for every 5–7 kg/m² rise in pre-pregnancy BMI11. Comprehending the link between obesity and the heightened risk of preeclampsia is essential for various reasons. Initially, it seems that obesity is the primary attributable risk factor for preeclampsia12,13. Since the evident solution for obesity, which is weight loss, is not suitable during pregnancy and only minimally effective when not pregnant, pinpointing factors that could mitigate obesity’s effects to lower the risk of preeclampsia would be very beneficial. While there is limited concrete information regarding how obesity relates to preeclampsia, some studies indicate that various lifestyle factors associated with obesity affect the likelihood of developing hypertensive disorders. The link between diet14, sleep disturbances15, and physical activity16 and cardiovascular disease is well recognized. The similarities between cardiovascular disease and preeclampsia warrant viewing mechanisms identified as significant factors of obesity related to cardiovascular disease as important areas for research to understand the pathophysiology of preeclampsia17.

Obesity and gestational diabetes are the most common conditions impacting mothers and their children throughout pregnancy. Both conditions have demonstrated a persistent rise in their occurrence in recent years, negatively affecting pregnancy outcomes and the long-term health of mothers. In line with our findings, being overweight heightens the risk of gestational diabetes18. Many studies have found a higher risk of gestational diabetes in overweight or obese women compared to those who are lean or of normal weight19,20. Although many studies consistently indicate a greater risk of gestational diabetes with increasing weight or BMI, the strength of the relationship remains unclear. Pregnancy can lead to various metabolic, biochemical, physiological, hematological, and immunological changes. Insulin’s ineffective response in glucose uptake and usage has been associated with both obesity and gestational diabetes21. Nonetheless, identifying the biological mechanisms linking maternal central obesity to the risk of gestational diabetes will require additional research.

The method of childbirth is one of the most important outcomes of each pregnancy. While every healthcare provider aims for a healthy mother and baby at the end of each pregnancy, ultimately, we all prefer a normal vaginal delivery that occurs without complications. The findings of our study showed that a higher BMI decreased the chance of spontaneous labor and vaginal delivery. Recent studies indicate a markedly elevated rate of induced labor and cesarean delivery among those with obesity22,23. Multiple predictive models have identified obesity as a key factor influencing the success of vaginal delivery after induced labor24. The increased likelihood of labor induction in obese women due to related health issues may explain why there are fewer vaginal deliveries among overweight and obese mothers.

Based on earlier research exploring the connection between maternal obesity and negative pregnancy outcomes, findings indicated that obesity poses a risk for maternal ICU admission25,26. Our results indicated that maternal ICU admission was an adverse event more prevalent among obese women. While our dataset did not specify the reasons for ICU admission, we believe that comorbidities such as preeclampsia could be a potential factor. Additional research into the reasons for transferring mothers to the ICU is essential .

Expectant mothers who are overweight or obese face a significant risk of delivering LGA infants27. Infants born LGA have a higher likelihood of developing into overweight or obese children, teenagers, and young adults, and they may also have a greater risk of experiencing metabolic syndrome in the future, as well as having LGA children themselves28. While our study’s findings indicated that instances of LGA were more common among overweight and obese mothers, the binomial logistic regression did not demonstrate an elevated risk of LGA associated with BMI.

It is clear that the likelihood of negative pregnancy outcomes increases with the level of weight gain; thus, preventative measures should aim to encourage women, particularly those who are already overweight, to lose weight before conception. Managing weight loss during pregnancy is crucial to prevent any unintended outcomes. Nonetheless, women frequently interact with health experts throughout pregnancy; therefore, dietary and lifestyle changes such as physical activity, which reviews and meta-analyses29,30 have shown can reduce gestational weight gain and enhance outcomes for mother and child, might be offered to them.

Certain studies distinguish between various obesity classifications, but in this research, the dataset we obtained did not categorize these classifications, and retrospective differentiation was not feasible; thus, all women with a BMI of 30 or greater were classified as having obesity. Another problem with our dataset was the absence of data related to weight gain during pregnancy, and this variable could also affect the pregnancy outcomes. Consequently, we advocate for a future study that considers these limitations for improved comprehension.

One limitation is its retrospective nature. To reduce selection bias, we made efforts to include all consecutive mothers who delivered babies during the study period. All women with a BMI of 30 kg/m2 or greater were deemed to have obesity; distinguishing between morbid obesity or obesity classes II and III from general obesity could not be achieved in our study. Adjustments were made in analyses for several significant potential confounders to assess the effect of high maternal weight on each outcome, which is a key strength of our study. Moreover, the examination of 20 outcomes in this research suggests the potential for Type I errors resulting from multiple comparisons. Since reanalysis with an adjusted significance level was not practical, these results should be viewed cautiously and regarded as hypothesis-generating, awaiting confirmation in future research with suitable statistical modifications. Additionally, the incorporation of various covariates in the regression models, especially for uncommon outcomes like preeclampsia, LGA, and maternal ICU admission, may have heightened the risk of overfitting. A significant advantage of this study is its fairly large sample size (n = 2,930 ), which offers adequate statistical power for identifying meaningful differences in maternal and neonatal outcomes, and the proper representation of each weight category improves the generalizability of our results.

Conclusion

Overweight or obese mothers face higher risks of negative pregnancy and delivery outcomes. The likelihood of these conditions increases with a higher body mass index. Health professionals should be equipped and educated to provide effective dietary and lifestyle interventions to women at risk of overweight or obesity prior to conception, thereby reducing associated risks and promoting optimal pregnancy and delivery outcomes.