The effects of the pre-pregnancy maternal body mass index on the pregnancy outcomes

Objective

The aim of our study is to investigate the effects of the pre-pregnancy maternal body mass index on the pregnancy and the neonatal outcomes.

Methods

The medical reports of 1038 pregnant women who attended and delivered in our clinic between January 2005 and October 2007 were analyzed retrospectively. The patients were grouped as low body weight, normal, over-weight and obese according to the American Food and Drug Association criteria by patients’ verbal reports. The gestational and the perinatal outcomes of the pregnants who have different body mass index were compared.

Results

The average of age, gravidity, and parity increase directly proportional with body mass index. When the body mass index increases the cesarean section is seen more as the birth way (p=0.02), and the cephalo-pelvic disproportion is seen as the major indication for cesarean (p=0.025). Laceration is seen more in obese patients at the birth (p<0.001). There has been no difference between the groups concerning the complications like uterine atony, meconium and preterm birth, but in obese group the need for neonatal intensive care unit is seen more necessary (p=0.003).

Conclusion

High pre-pregnancy maternal body mass index is associated with more operative birth and neonatal problems. To begin the pregnancy with an ideal body weight will make better results for both mother and baby.

Keywords

Body mass index, perinatal outcome, operative birth

Introduction

Obesity, which is defined as the disease of modern era, is a serious health issue frequently increasing in our society as well as in the world. Obesity is a multifactorial disorder which is related with malnutrition, limited physical activity, metabolism rate and genetic factors. Obesity has negative effects during pregnancy as well as increasing morbidity and mortality in terms of many diseases. It is known that obesity may cause infertility, polycystic ovary syndrome, irregular menses, gestational issues during pregnancy, obstetric complications and neonatal negative results.(1) Body mass index (BMI) calculated by dividing body weight by the height squared is used to evaluate the obesity. BMI values obtained during the period before pregnancy or on first trimester should be used for the evaluation of pre-conceptual obesity.(2) While it was reported that the maternal obesity and overweight in pregestational period are related with obstetric complications such as gestational diabetes, hypertension, preeclampsia, macrosomia and high cesarean rate, it was found that the body weight under normal scales (weak) is related with fetal growth limita-tion.(3-9) The purpose of this study is to research the relation of pre-conceptual maternal BMI with obstetric complications and the effects on perinatal outcomes.

Methods

Archive files of all women who completed their 182nd-293rd gestational days and delivered in our clinic between January 2005 and October 2007 were analyzed retrospectively in order to include into the study. Patients who came for their first examination after first trimester and did not remember their pre-pregnancy weights exactly, cases with multiple pregnancies, cases with maternal systemic disease, cases who had placenta previa, cases with decollement placenta and cesarean cases who had excesarean, rectal primipara or posttreatment gestation as primary indication were excluded from the study in case that delivery time and weight could be affected. Similarly, pregnant who did not have antenatal follow-up in our polyclinic and applied to our clinic for the first time at delivery were excluded from the study. Totally 1038 patients who measured up were included into our study. Body mass indexes were calculated by pregestational weight and height measurements reported by patients verbally on the first visit to hospital after they got pregnant. Body mass index was calculated by dividing body weight (kg) by the height (m) squared. Values accepted by American Food and Drug Association were used for classification of obesity. According to this classification, women with BMI equal or below 18.4 kg/m2 were considered as under-weight, while between 18.5 and 24.9 kg/m2 were considered as normal, between 25 and 29.9 kg/m2 as overweight and above 30 kg/m2 as obese. Perinatal results of groups having dif-ferent BMI values were compared. Statistical analysis of data was done by using Statistics Package for Social Sciences version 11.0 (SPSS Inc., Chicago, IL). ANOVA (Tukey HSD Multiple Comparison) was used to compare averages among groups and multiple chi-square test was used to compare rates. Pearson correlation test was operated to evaluate the relation between BMI and the averages of groups while logistic regression analysis was done for effects of con-founding factors in multivariate analyses. Data was given as average and standard deviation (±SD). Type 1 error grade was accepted as 0.05.

Results

Totally 1038 patients were included into the study. There were 104 patients (10%) in the underweight patient group (Group 1), 764 patients (73.6%) in the normal patient group (Group 2), 140 patients (13.5%) in overweight patient group (Group 3) and 30 patients (2.9%) in obese patient group (Group 4).
BMI, age, gravida, pregnancy period, delivery weight and parity averages of groups were shown in Table 1. Average pregnancy period and average delivery weights among groups were similar; however, it was also observed that gravida and parity rates increased together with the BMI increase (p=0.02; p=0.043, respectively). Mean age was statistically and significantly increasing as BMI was increasing among the groups (r=0,323, p=0,0001, respectively) (Fig. 1).
When delivery types and cesarean rates of groups were compared (Table 2), it was seen that cesarean rates were increasing statistically and significantly as BMI was increasing (p=0.02) and there was statistically significant difference in terms of cephalopelvic disproportion when cesarean indications among groups were examined (p=0.025). Increased cesarean rate due to cephalopelvic disproportion was also found as significant in logistic regression analysis which was performed by using con-founding factors (age, gravida, parity, pregnancy period, delivery weight) ((3=0.621; OR:1.53 95%CI 0.22-9.08, p=0.04).
Statistically no significant difference was found among groups when they were compared for early labor rates (p=0.431 and p=0.473, respectively). Statistically no significant difference was found among groups when atony follow-up rates were compared (p=0.438) and amnios fluid rates stained with meconium (p=0.289). Laceration rates were statistically and significantly increasing as BMI increased (p<0.001) when postnatal laceration rates were compared.
When the rates of application to newborn intense care unit in groups were compared, it was seen that there was statistically a significant difference as it was higher in Group 4 (p=0.003). Similarly, this difference kept its sig-nificance in logistic regression analysis ((3=1.316, OR: 1.84 95%CI 0.13-4.67, p=0.005).

Discussion

Results of this study show that pre-gestational BMI values increase cesarean rates due to cephalopelvic disproportion, postnatal laceration rates and the rates of being taken to new-born unit of baby.
Obesity is an important public health issue today. Fetal and maternal complications are seen more frequently with the addition of gestational period in which metabolic functions completely change.Chronic medical problems which already exist due to obesity in pregestational period cause more antenatal,peripartum and neonatal negative conditions with the pregnancy for both mother and baby compared to women who have normal pre-gestational body mass.
Although classification according to pre-gestational Body Mass Index is important in terms of perinatal outcomes, weight increase in gestational period can be significantly effective.(3-7) On the other hand, it was shown in the retrospective study performed by Edwards et al.(8) on 1273 cases (683 obese and 690 normal BMI) that there is no relation between the differences of weight gaining during pregnancy and gesta-tional complications.
It was shown in the study performed on 245.000 cases in 2006 by Cedergren et al.(9) that obese pregnants who gain less weight during gestational period have lower risk of laboring big baby and overweight and obese pregnants who gain more weight during gestational period have higher risk of laboring big baby. It was shown that differences of gaining weight during gestational period affected obstetric outcomes more than pre-gestational body mass index.
The constraint of our study is that it does not reflect the weight gaining differences during gestational period. However, the risk of laboring big baby was found as high in overweight and obese pregnants compared to pregnants who had normal body mass index during pre-gestational period, and this difference is statistically significant.
It is also seen in the study of Cedergren et al.(9) that there is an increase in cesarean delivery rate in obese and morbid obese pregnants who have high weight gaining and the risk of operative labor increases in overweight pregnants.
In the study of Doherty et al.(10) the rates of cesarean delivery frequency, gestational diabetes and delivery induction were higher in overweight and obese pregnants compared to those with pre-gestational normal body mass index. Although obese women have the risk of delivering baby with intrauterine growth retardation (IUGG) (especially in hypertensive-preeclamptic cases), there is rather a common consensus that they deliver big baby. Irvine et al.(11) reported that fetal macrosomia incidence is higher in obese women and this causes obstetric complication development. In the study of Vahratian et al.(12) it was seen that unplanned cesarean rate was higher in obese and overweight pregnants compared to pregnants with normal body mass index. They showed that approximately 1.2 fold of cesarean delivery in overweight pregnants and approxi-mately 1.5 fold of cesarean delivery in obese pregnants are required. They also stated that these cesarean indications were caused by acute fetal distress and dystocia. It was seen that more dystocia developed by the elongation of the first phase of delivery and this was based on the non-development of the case despite the 2 fold of period compared to normal delivery. In our study, it is seen that cesarean rate increases as pre-gestational body mass index increases. This is related with the increases of body mass index and macrosomic baby development and the increase of the occurrence of cephalopelvic disproportion. At the end of our study, an increase was seen in macrosomia and cephalopelvic disproportion as body mass index increased and this increase was found statistically significant. Acute fetal distress and induction failure were found as other cesarean reasons but they were not found statistically significant. At the same time, the risk of laceration occurrence at delivery is high in babies of obese patients and this is related with macrosomia.
According to the study of Doherty et al.,(10) the rate of delivering baby with IUGG is higher in patients who are evaluated as underweight as to body mass index. Also the study of Cedergren et al.9 showed that the rate of delivering baby with IUGG is higher in cases with low weight gaining during gestational period who were obese in pre-gestational period. In the study of Maddah,(13) less rate of babies with low birth weights were seen in pregnants with low pre-gestational BMI and low weight gaining during gestational period compared to pregnants with normal BMI in both groups. In our study, this rate was higher in underweight patient group but it was not found statistically significant.
According to the study of Doherty et al.,(10) neonatal adverse effects such as delivery induction rate, perineal traumas and neonatal hypo-glycemia, neonatal resuscitation and low Apgar score which require special care increase as BMI increases in normal pregnancies which do not include complications induced by pregnancy such as hypertension. In our study, no increase was observed in the risk of early labor in pregnants as BMI increases. However, rates of being taken to newborn unit of babies increase as pre-gestational body mass index increases.

Conclusion

At the end of our study, we determined that cesarean rates increased due to cephalopelvic disproportion, postnatal laceration rates increased and the rates of being taken to new-born unit of baby increased as pre-gestational BMI values increased. Maternal adverse effects related with weight changes and neonatal outcomes are related with pre-gestational body mass index as well as weight amount gained during gestational period. Body mass index increases with age, gravida and parity of pregnants. Beginning to become pregnant with an ideal BMI would minimize traumas to be exposed by mother and baby and help us to reach a healthy mother and a healthy baby which is the primary obstetric purpose.

References

1) Gonzalez A, Toy EC, Baker B. The evaluation and treatmant of the overweight patient.Prim Care Update Ob Gyns 2000;7(6):224-30.
 2) Harris HE, Ellison GT.Practical approaches for estimating prepregnant body weight.J Nurse Midwifery 1998;43(2):97-101.
3) Thorsdottir I, Torfadottir JE, Birgisdottir BE, Geirsson RT.Weight gain in women of normal weight before pregnancy: complications in pregnancy or delivery and birth outcome.Obstet Gynecol 2002;99(5 Pt 1):799-806.
4) Stotland N, Washington AE, Caughey A. Pre-pregnancy body mass index and length of gestation at term .Am J Obstet Gynecol 2007;197(4):378.e1-5.
5) Graves BW, DeJoy SA, Heath A, Pekow P .Maternal body mass index, delivery route, and induction of labor in a midwifery caseload. .J Midwifery Womens Health 2006;51(4):254-9..
 6) Cogswell ME, Serdula MK, Hungerford DW, Yip R.Gestational weight gain among average-weight and overweight women-what is excessive? .Am J Obstet Gynecol 1995;172:705-12.
7) Scholl TO, Hediger ML, Schall JI, Ances IG, Smith WK.Gestational weight gain, pregnancy outcome, and postpartum weight retention.Obstet Gynecol 1995;86(3):423-7.
8) Edwards LE, Hellerstedt WL, Alton IR, Story M, Himes JH.Pregnancy complications and birth outcomes in obese and normal-weight women: effects of gestational weight change.Obstet Gynecol 1996;87(3):389-94.
 9) Cedergren M .Effects of gestational weight gain and body mass index on obstetric outcome in Sweden.Int J Gynaecol Obstet 2006;93(3):269-74.
10) Doherty DA, Magann EF, Francis J, Morrison JC, Newnham JP .Pre-pregnancy body mass index and pregnancy outcomes .Int J Gynaecol Obstet 2006;95(3):242-7.
11) Irvine L, Shaw R.The impact of obesity on obstetric outcomes.Current Obstet Gynecol 2006;16:242-6.
 12) Vahratian A, Siega-Riz AM, Savitz DA, Zhang J.Maternal pre-pregnancy overweight and obesity and the risk of cesarean delivery in nulliparous women .Ann Epidemiol 2005;15(7):467-74.
13) Maddah M.Pregnancy weight gain in Iranian women attending a cross-sectional study of public health centres in Rasht .Midwifery 2005;21(4):365-70.

	File/Dsecription
	Figure 1. Positive correlation between BMI and age.
	Table 1. Demographic data of groups according to BMI values.
	Table 2. Delivery types and cesarean indications among groups.