Acute Effects of Maternal Exercise and the Growth Restricted Pregnancy

Background and Significance

Regular exercise during pregnancy is beneficial in many ways, including decreased rates of diabetes or hypertensive disorders and decreased risks of preterm birth and cesarean deliveries. Many people use exercise to treat anxiety and depression as well as meet gestational weight gain recommendations. Regular exercise, defined as 150 minutes of moderate intensity exercise per week, is recommended in uncomplicated pregnancies. In some summary statements, fetal growth restriction (FGR) is noted as a relative or absolute contraindication to regular exercise. The American College of Obstetrics and Gynecology (ACOG), however, does not list FGR as a contraindication to maternal exercise. Currently, there are few high-quality studies about the effect of a recommended amount of maternal exercise on acute fetal status in pregnancies affected by FGR. The existing theories conflict. One theory is that maternal exercise will divert blood flow away from the uterus/fetus which could be deleterious in an already compromised pregnancy. The other theory is that exercise increases cardiac output and would therefore increase blood flow to the fetus. A previous study evaluated growth restricted fetuses after a single 5-minute bout of maternal exercise. This study population was heterogenous and used non-standardized measures of fetal assessment, making the results difficult to clinically interpret. In a previous study of healthy pregnancies, 30 minutes of moderate maternal exercise has been determined to have no effect on acute fetal status. The current study seeks to understand the acute fetal response to a single maternal exercise episode in pregnancies affected by FGR.

Inclusion criteria

• Inclusion Criteria - FGR population

• Age 18-45
• Intrauterine pregnancy with diagnosis of fetal growth restriction (FGR) as defined by total estimated fetal weight <10%ile for EGA or abdominal circumference <10%ile for EGA
• Diagnosis of FGR at any point in gestation (preference given for inclusion of those diagnosed with FGR after 32w0d)
• Gestational age between 28w0d and 36w6d at time of intervention (based on sure last menstrual period (LMP) confirmed by first or second trimester ultrasound or unsure LMP with first trimester ultrasound)
• Compliant with standard prenatal care

Inclusion criteria

- Average for gestational age (AGA) population

• Age 18-45
• Intrauterine pregnancy with normal estimated fetal growth (EFW >10%ile and <90%ile)
• Gestational age between 28w0d and 36w6d at time of intervention with accurate dating (based on sure LMP confirmed by ultrasound prior to 22 weeks or unsure LMP with first trimester ultrasound)
• Compliant with standard prenatal care

Exclusion criteria

• Exclusion Criteria - FGR population

• Known contraindication to completion of 30 minutes of moderate intensity exercise
• Fetal umbilical artery with elevated S/D ratio or absent or reversed diastolic flow
• BMI >40
• Severe maternal anemia (Hb less than 8.0)
• Placenta previa
• 2nd or 3rd trimester vaginal bleeding
• Preterm premature rupture of membranes
• Cervical insufficiency
• Multi-fetal gestation
• Oligohydramnios
• Hypertensive disorder requiring antihypertensive medication
• Blood pressure >140/90 on the day of the study visit prior to exercise
• Tobacco use
• Opioid agonist therapy
• Known fetal chromosomal anomaly, structural anomaly or infection
• Inability or unwillingness of subject to give informed consent
• Current psychiatric illness/social situation that would limit compliance with study requirements, as determined by the principle investigators

Exclusion criteria

- AGA population

• Known contraindication to completion of 30 minutes of moderate intensity exercise
• BMI >40
• Severe maternal anemia (Hb less than 8.0)
• Placenta previa
• 2nd or 3rd trimester vaginal bleeding
• Preterm premature rupture of membranes
• Cervical insufficiency
• Multi-fetal gestation
• Oligohydramnios
• Hypertensive disorder requiring antihypertensive medication
• Blood pressure >140/90 on the day of the study visit prior to exercise
• Tobacco use
• Opioid agonist therapy
• Known fetal chromosomal anomaly, structural anomaly or infection
• Inability or unwillingness of subject to give informed consent
• Current psychiatric illness/social situation that would limit compliance with study requirements, as determined by the principle investigators