The findings of present retrospective cohort study indicated an increased risk for LGA, LBW and macrosomia in overweight mothers and an increased risk of SGA in the mothers with GWG below IOM guidelines.
The average of GWG was similar to the IOM recommendations in normal BMI mothers during, the 2nd and 3rd trimester of pregnancy, and was different with IOM guidelines in other groups of pre-gestational BMI during mid- or late-pregnancy.
Due to the little number of underweight mothers, it was not possible to make an association between GWG, pre-pregnancy BMI and birth weight status. In normal weight mothers, a high risk of SGA was significantly associated with inadequate GWG. In agreement with the previous studies, an increased risk of LGA[19, 20], LBW[21], and macrosomia [21, 22] was observed in overweight mothers with GWG outside guidelines, significantly.
The prevalence of GWG above the IOM recommendations was more common, in comparison with the below one, which is in agreement with the results reported by Power et al.[20]. In our study 46.4% had weight gain greater than IOM recommendation. Also, in recent systematic meta-analysis reported 47% GWG above guidelines [9].
Inadequate GWG was related to a high risk of SGA and LBW, consistent with a longitudinal cohort studies in China [23], Taiwan[24], and higher pre-gestational BMI increased risk for LGA and macrosomia were reported in overweight/obese mothers [25], which are in agreement with the findings of the present study.
in our study higher pre-BMI was associated with higher risk of adverse birth weight. In agreement, lima et al. [26], showed an increasing trend for the birth weight across higher pre-pregnancy BMI.
Moreover, the prevalence of macrosomia (6.2%) was higher in Ahvaz than the mean of Iran (5.2%) [27] and lower than a pervious retrospective hospital- based (2007–2011) study conducted in Razi Hospital, Ahvaz city was reported 9% [15].
Likewise, increasing pre-pregnancy BMI was associated with the risk of higher fasting blood glucose between 24–28 weeks of pregnancy. In addition, higher risk of GDM was associated with higher rate of macrosomia. Consistent with our findings, a study among 256 pregnant women in the United Arabia Emirate reported that pre-pregnancy BMI ≥ 25 kg/m2 were at higher risk of having GDM [28]. In agreement with our findings, a meta-analysis of 33 observational studies indicated that risk of GDM is positively associated with pre-pregnancy BMI [29]. however, the result of a study on Asian indicated that obese Thai women were not at increased risk for gestational diabetes mellitus was in contrast with result of present study [30].The possible reason of this difference is due to the WHO’s recommended BMI for Asians was used to define obesity.
In addition, our study and another studies [31, 32] showed that gestational hyperglycemia had a positive association with macrosomia.
The possible mechanisms of the high risk of adverse birth weight in high weight mothers could be due to the stimulating of insulin production in overweight mothers, therefore, lipogenesis and fat deposition would be increased in their offspring, so it can alter the growth of the fetus [33].
In the present study, we attempted for having large possible sample size from different health care centers to cover all ethnic groups together including Fars, Lure, Arab, and Bakhtiari. However, the exact number of different ethnic groups is not included in maternal records. So, we had limitation to explore ethnic differences in pre-pregnancy BMI, prevalence of GWG below or outside IOM guidelines and pregnancy outcomes.
In addition, pairs of mother and child document since 2010 to 2018 were taken into account and it could be highly reflect the current situation. pre-pregnancy weight was recorded from antenatal records, and it may be measured by health member or self-reported leading to the risk of recall bias, which is in line with other studies [26]. However, they were valid to be used in epidemiologic study [34]. Moreover, in the current study the 2009 IOM guideline was applied for GWG based on pre-pregnancy BMI. Furthermore, the recent meta-analysis [35] included 23 studies, explored ethnic differences based on IOM guidelines and regional guidelines in maternal pre-pregnancy BMI and GWG on pregnancy outcome across the USA, Western Europe and East Asia. However, there was data restriction from Middle East. In fact, the IOM approaches are primarily based on USA-dwelling, showed limited data on ethnic differences in associations between GWG and pregnancy outcomes. Then, led to heterogeneity and diminished the chance of comparisons across regions. Asia is the most inhabitant of the world’s population. In 2004 WHO consultation group [36] reported, Asians may have higher odds of disease at a BMI cut-off (lower than 25 kg/m2). Likewise, Asians are likely to have a higher percent of adipose tissue, especially visceral adiposity, at lower BMI cut-off points than that stated by the WHO as standard cut-off points [37]. In particular, finding of recent study showed that Iranians are at higher risks of morbidity related to metabolic factors at a lower BMI cut-off with an estimated 38.8% of the population having metabolic syndrome [38]. Importantly, the significant difference in Asian countries is based on ethnic and cultural subgroups, degrees of urbanization, social and economic conditions, and nutrition transitions [36].Therefore, establishing a new guideline and GWG recommendation for Asian populations is necessary for optimal risk reduction during pregnancy [24].
In the present study the information related to socio-demographic and lifestyle characteristics (alcohol consumption and smoking) were not accurate due to their social beliefs.
According to the literature, this is the first study in public health care centers in South-west of Iran that present the association between GWG and pre-pregnancy BMI with adverse pregnancy outcome.
Thus, screening for overweight and obesity is an important preventive approach. It seems that along with all gestational monitoring and nutrition counseling, more educational programs in the health care centers are vital, due to the presence of multiple ethnic groups in Ahvaz city with different cultural habits.