Maternal Obesity and Small for Gestational Age Infants
Condition: Obesity; Small for Gestational Age
MeSH terms: Obesity
Study type: Observational

Summary: 
      The purpose of this retrospective pilot study is to address the effect that obesity, in the
      absence of other comorbidities, has on birth weight. We wish to determine if obesity is a
      risk factor for small for gestational age (SGA) or intrauterine growth restricted (IUGR)
      infants in our clinic population. There have been many studies linking maternal obesity with
      fetal macrosomia, defined as fetal birth weight greater than 4500 grams. However, we have
      noted that a percentage of our obese patient population has delivered either an SGA or IUGR
      infant. SGA refers to a constitutionally small infant weighing less than the 10th percentile
      for age. This refers to a genetically normal infant. IUGR refers to a fetus whose growth has
      been restricted by influences other than normal genetics.

      Our study population will consist of all women over the age 18 who delivered a term infant
      either by vaginal delivery or cesarean section at Tulsa Regional Medical Center between July
      1st 2004 and December 31st 2005.

      The diagnosis of obesity will be based upon a Body Mass Index (weight in kilograms/height in
      meters squared) of thirty or greater. We will look at the infant birth weight as recorded in
      the patient's chart. We will define SGA or IUGR as birth weight less than the 10th percentile
      for gestational age as defined previously. The control group will consist of women meeting
      the same criteria except they will have a BMI less than thirty but greater than 19.8 as low
      maternal weight is also a risk factor for IUGR. We will compare the average birth weight and
      the rates of SGA/IUGR infants between the two groups and analyze using the chi-squared method
      of analysis.
    

Detailed description: 
      The purpose of this retrospective pilot study is to address the effect that obesity, in the
      absence of other comorbidities, has on birth weight. We wish to determine if obesity is a
      risk factor for small for gestational age (SGA) or intrauterine growth restricted (IUGR)
      infants in our clinic population. There have been many studies linking maternal obesity with
      fetal macrosomia, defined as fetal birth weight greater than 4500 grams. However, we have
      noted that a percentage of our obese patient population has delivered either an SGA or IUGR
      infant. SGA refers to a constitutionally small infant weighing less than the 10th percentile
      for age. This refers to a genetically normal infant. IUGR refers to a fetus whose growth has
      been restricted by influences other than normal genetics. Obesity is defined as a body mass
      index (BMI) greater than 30 by the World Health Organization and the National Institutes of
      Health. This is a relevant topic in health care today as one-third of adult women fall into
      the category of obese. As this number increases, we will be faced with the challenge to
      provide comprehensive prenatal care to these women. Risk factors for IUGR in particular
      include hypertension, renal disease, restrictive lung disease, diabetes, cyanotic heart
      disease, antiphospholipid syndrome, collagen vascular disease, hemoglobinopathies, tobacco
      and drug use, severe malnutrition, placental disease, multiple gestation, infection, genetic
      disorders, and teratogenic exposure. The children born with this condition are at greater
      risk for hypothermia, hypoglycemia, apneic episodes, seizures, sepsis, and neonatal death.
      Long term problems usually develop based on the cause of the SGA or IUGR status with most
      catching up growth-wise to other children their age. Previous studies have linked these
      conditions to higher incidence of hypertension and cardiovascular problems. The most basic
      screening for these conditions is the simple fundal height measurement, as the most likely
      physical finding will be uterine size less than dates. It is questionable how accurate this
      measurement is in the obese population as the measurement is taken over the layer of
      abdominal fat. Obesity in the pregnant patient is linked to increased rates of hypertension,
      preeclampsia, and gestational or preexisting diabetes. Although many studies have also linked
      fetal macrosomia to maternal obesity, there have been studies published within the last year
      that relate maternal obesity with SGA or IUGR infants. A Danish study looked at a cohort of
      women who delivered singleton infants. They looked at pregnancy complications including
      diabetes, hypertension, preeclampsia, and cesarean delivery. The study population included
      only deliveries from 37-42 weeks gestation. Women with hypertension and preexisting diabetes
      were included in the study population. The findings included higher risk of macrosomic
      infants in the general study population. In a small segment of the study population, however,
      they found increased incidence of SGA infants but not IUGR infants. This hints at a possible
      relationship between obesity and SGA but does not control for other variables. A study out of
      Medical University of South Carolina looked at prepregnancy weights and subsequent weight
      gain. It was a cohort study using birth certificate information linked to the South Carolina
      Pregnancy Risk Assessment Monitoring System, a system of telephone and mail survey, to
      collect the data for this study. The results included a 1.8 times greater likelihood of an
      obese woman delivering a very low birth weight infant (3).

      Study Population Inclusion/Exclusion Criteria Our study population will consist of all women
      over the age 18 who delivered a term infant either by vaginal delivery or cesarean section at
      Tulsa Regional Medical Center between July 1st 2004 and December 31st 2005. We choose this
      time frame as we feel this will give an adequate sample size of approximately about 160 women
      in the study group and about 260 in the control group, while allowing for completion of the
      project within 12 to 18 months. Our statistician, Dr. Mark Payton, has completed a power
      analysis for these numbers, and it is included with our submission. We will define a term
      infant as 37 weeks gestation or greater. They must have had at least one visit at the Houston
      Park Ob-Gyn clinic, not including the initial prenatal lab visit, before delivery. Our study
      population will consist of mainly Medicaid patients, most of who are of lower socioeconomic
      status. The ethnic blend of our study population will include Caucasian, African-American,
      Hispanic, American Indian, and Asian women. Our study population will have a BMI greater than
      or equal to 30 based on initial recorded weight and recorded height. We will exclude women
      with multiple gestation, hypothyroidism, hyperthyroidism, heart disease, tobacco or drug use,
      gestational or preexisting diabetes, autoimmune disease of any form, hypertension, collagen
      vascular disease, any disease process resulting in decreased gastrointestinal nutrient
      absorption, or lung disease as these are conditions known to be risk factors for IUGR (5).

      Early Termination Criteria N/A

      Methods/Procedures Diagnosis The diagnosis of obesity will be based upon initial weight and
      height recorded in the patients chart, typically during the first trimester, to derive a BMI
      (weight in kilograms/height in meters squared). Although total weight gain during a term
      pregnancy could add enough to the BMI to falsely indicate obesity, since we will be using the
      initial weight recorded, this difficulty should be minimized. The cutoff for our study group
      will be a BMI of thirty or greater as this is the definition of obesity by the World Health
      Organization and the National Institutes of Health. We will look at the infant birth weight
      as recorded in the patient's chart. We will define SGA or IUGR as birth weight less than the
      10th percentile for gestational age as defined previously. The control group will consist of
      women meeting the same criteria except they will have a BMI less than thirty but greater than
      19.8 as low maternal weight is also a risk factor for IUGR.

      Data Collection The collaborating investigators and research assistants will collect only the
      following information from the patients chart: age, height, weight at initial visit, date of
      delivery, infant birth weight, smoking status, and any of the abovementioned comorbidities
      that would exclude the patient from the study. No other data will be collected from any
      patients chart. We will utilize research assistants in the collection of this data, and these
      research assistants will be OSU medical students employed by the work study program to work
      on this project. They will be collecting data from clinic records. They have basic human
      research and HIPAA training and are allowed access to patient chart information as they fall
      under the OSU community of individuals with this privilege. Analysis We will compare the
      average birth weight and the rates of SGA/IUGR infants between the two groups. We will
      analyze the results using chi-squared method of analysis.

      Confidentiality The clinic records to be reviewed will be kept in the Houston Park medical
      records department which is either locked or under security supervision at all times. The
      hospital records will be kept in the Tulsa Regional Medical Center health information
      management department. This department is locked 24 hours a day. No identifying information
      from any individual's chart will be recorded, so de-identification will occur when the data
      is collected, and no master list of patient names or other identifying information will be
      kept.
    

Time perspective: Retrospective
Keywords: obesity; small for gestation age; intrauterine growth restriction