Fetal Growth Discrepancies: What to Expect During Pregnancy

Fetal macrosomia

Dear Doctor: I am currently 26 weeks pregnant.
During my last ultrasound, which was around 27 weeks, the baby weighed approximately 1080 grams.
After a week, I went to another hospital for a check-up, and the baby was estimated to be around 29 weeks and weighed 1450 grams.
Why did the weight increase so significantly? Could this have any impact on the fetus? Is it common for there to be such a large discrepancy in measurements between two hospitals?

99, 30~39 year old female. Ask Date: 2012/06/06

Dr. Liu Yuhong reply Obstetrics and Gynecology

Measuring fetal weight via ultrasound within a short time frame (less than 2 weeks) will inevitably result in discrepancies! Different examiners, the gestational age at the time of the examination, varying ultrasound machines, as well as the fetal position and amniotic fluid volume during the scan, are all potential sources of error.
This is also why prenatal check-ups covered by health insurance (codes: 41, 42, 43, 44, 45) are scheduled every 4 weeks during early to mid-pregnancy.

Reply Date: 2012/06/06

More Info

Understanding fetal growth discrepancies during pregnancy can be quite concerning for expectant parents. It is important to recognize that variations in fetal measurements can occur due to several factors, including differences in ultrasound techniques, the timing of the scans, and the inherent variability in fetal growth patterns.

Firstly, it is essential to understand that fetal growth is not always linear. During pregnancy, especially in the second and third trimesters, fetuses can experience growth spurts. This means that a fetus may appear to gain weight rapidly over a short period, which can sometimes lead to confusion when comparing measurements from different ultrasound examinations. In your case, the increase from 1080 grams to 1450 grams in just a week could be attributed to a natural growth spurt.
Moreover, the gestational age at which the ultrasounds were performed can also play a significant role. Different ultrasound machines and operators may have slightly different methods for estimating fetal weight and gestational age. For instance, if the first ultrasound was performed slightly earlier than the second, the growth may appear more pronounced in the second scan. Additionally, the accuracy of ultrasound measurements can vary, particularly in the later stages of pregnancy when the fetus is larger and more difficult to measure accurately.

It is also important to consider the potential for discrepancies in the way the two hospitals calculate fetal weight. Each facility may use different formulas or reference charts to estimate fetal weight based on measurements taken during the ultrasound. This can lead to variations in the reported weight and gestational age.
Regarding the impact of these discrepancies on fetal health, it is generally reassuring to note that as long as the fetus is growing and developing within a reasonable range, fluctuations in weight estimates are typically not a cause for concern. However, it is crucial to maintain regular prenatal care and follow-up ultrasounds to monitor fetal growth trends over time. If there are significant concerns about growth discrepancies or if the fetus is consistently measuring smaller or larger than expected, your healthcare provider may recommend additional evaluations, such as Doppler studies to assess blood flow or further imaging to rule out any underlying issues.

In conclusion, while it can be alarming to see significant differences in fetal weight measurements between two ultrasounds, it is often a normal part of pregnancy. The best course of action is to continue regular prenatal visits, maintain open communication with your healthcare provider, and trust that they will monitor your baby's growth closely. If you have any specific concerns about your pregnancy or the health of your baby, do not hesitate to discuss them with your obstetrician, who can provide personalized guidance based on your unique situation.

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