From the Guidelines
The average fetal weight gain per week is approximately 225 grams or 8 ounces until about 37 weeks of gestation. This information is based on the most recent guidelines from the Society for Maternal-Fetal Medicine 1.
Fetal Growth Patterns
Fetal weight gain varies throughout pregnancy, with a gradual increase as pregnancy progresses.
- During the first trimester, weight gain is minimal, only a few grams per week.
- In the second trimester, fetuses typically gain about 45-70 grams per week.
- The third trimester sees the most significant growth, with fetuses gaining approximately 225 grams per week until about 37 weeks, after which the rate may slow slightly.
Factors Influencing Fetal Growth
Individual growth patterns may vary based on several factors, including:
- Maternal factors such as nutrition and health
- Genetics
- Overall health of the pregnancy The most rapid weight gain occurs between 28-37 weeks when the fetus is depositing fat under the skin, which helps with temperature regulation after birth.
Clinical Guidelines
The Society for Maternal-Fetal Medicine recommends the use of population-based fetal growth references, such as Hadlock, in determining fetal weight percentiles 1. This guideline is crucial in assessing fetal growth restriction (FGR) and making informed decisions about pregnancy management.
Pregnancy Management
In cases of FGR, the society recommends serial umbilical artery Doppler assessment to assess for deterioration 1. The frequency of Doppler evaluation may vary depending on the severity of FGR and the presence of other risk factors. Weekly umbilical artery Doppler evaluation is recommended for pregnancies with severe FGR (EFW less than the 3rd percentile) or decreased end-diastolic velocity 1.
From the Research
Fetal Weight Gain
- The average fetal weight gain per week is not explicitly stated in the provided studies 2, 3, 4, 5, 6.
- However, study 3 mentions that the recommended energy intake for pregnant women depends on their pre-gravid body mass index (BMI) and trimester, which can indirectly affect fetal weight gain.
- Study 6 discusses the tracking of fetal growth characteristics during different trimesters and their association with birth outcomes, but does not provide a specific value for average fetal weight gain per week.
Fetal Growth Restriction
- Fetal growth restriction is defined as an estimated fetal weight (EFW) that is below the 10th percentile for gestational age 2, 4, 5.
- Study 4 investigates the use of maternal serum protein and ultrasound measurements at diagnosis to predict fetal or neonatal death and other adverse outcomes in cases of early-onset fetal growth restriction.
- Study 5 evaluates the relationship between Doppler and biometric ultrasound parameters measured at diagnosis and perinatal adverse outcome in a cohort of late-onset growth-restricted fetuses.
Ultrasound Measurements
- Ultrasound measurements, such as estimated fetal weight (EFW) and umbilical artery Doppler velocimetry, are used to guide pregnancy management decisions and predict fetal outcomes 2, 4, 5.
- Study 5 finds that EFW percentile at diagnosis is associated independently with composite adverse perinatal outcome (CAPO) and NICU admission.