In recent years, fetal growth restriction (SGA) has become a hot topic in the fetal medicine. It is important to assess fetal size to determine the presence of SGA during prenatal examination. However, the recognition ability for SGA and FL by the most common evaluation indicator Hadlock's is not satisfactory. This large-scale validation study, which includes approximately 32000 ultrasound scans, also indicates that the full-term use of the Hadlock reference curve has poor ability to identify fetal dwarfism, insufficient diagnosis of SGA in the early stages of pregnancy, and over diagnosis in the late stages of pregnancy. For example, in our database, an additional 3.6% (6.6% -3.0%) and 5.9% (8.9% -3.0%) of pregnancies were misclassified as short femur and small head at 34 to 40 weeks, respectively, which may require further unnecessary investigation and increase parental expense and anxiety.
Hadlock, as a short diameter method, aims to evaluate fetal size by measuring multiple indicators such as head circumference, abdominal circumference, and femoral length.[13] However, the Hadlock method is not as accurate in identifying SGA and FL. A French study of over 14,000 singleton births showed that Hadlock's sensitivity in identifying SGA was less than 50%.[14] This indicates that it can only correctly recognize about half of SGA fetuses. This is mainly because the SD (standard deviation) in the Hadlock method usually adopts a constant value, and this can lead to individual fetal growth not fitting in line with the actual situation. There are also racial differences, which are inconsistent with the results of other countries. For example, studies in Peru and South Korea have found that the error of the Hadlock method may be significant, and in many cases, systematic corrections are needed to obtain more accurate prediction results. [15, 16] Some studies also indicate that the Hadlock method is not entirely applicable to the Chinese population. [5, 17] The results of a nationwide cross-sectional study show that IG-21st standard is more suitable for fat free bioassay than other reference standards, especially HC, but not for fat bioassay, such as abdominal circumference. [18] The proportion of AC below the third Percentile is only 1%. This discovery has also received research support from European countries such as France, Greece, the Netherlands, Norway, Italy, and the United States. [19–21] Clearly, Socioeconomic status is the main determinant of fat based growth.
We established growth curves for neonatal weight, head circumference, body length, and abdominal circumference using various statistical methods based on cross-sectional and retrospective data. We found that there are significant differences and characteristics in indicators such as newborn height and weight in China compared to other standard curves (such as WHO). At the same time, there are also certain differences in the growth curves among different regions and seasons. Compared with other fetal growth curves, our results have the following advantages: First, we excluded Complications of pregnancy and fetal factors, such as congenital abnormalities and stillbirth, to ensure the accuracy and reliability of the data. At the same time, we used large-scale data collection and statistical analysis to conduct detailed research on the entire pregnancy cycle with broad coverage, in order to obtain more accurate growth curves. Secondly, compared with other similar studies, our sample has a more diversified population structure, including people from different regions, races, ages, education levels and socioeconomic status. This diversity not only reflects the differences and diverse characteristics of health status in different regions, but also provides more accurate reference standards for various populations. In this way, our research results can be promoted and applied for Chinese population. Finally, our research results are not just a fetal growth curve table, but a research platform that contains a large amount of medical information. In addition to providing standard growth curves, it is also possible to conduct in-depth discussions on the impact of different factors on fetal development, providing better guidance and treatment plans for medical institutions and doctors. We believe that this platform will have a positive impact on the development of infant and child health care.
However, we also acknowledge several limitations. Firstly, this is a retrospective study of analysis, without real-time tracking and monitoring, there may be a small amount of bias. Secondly, our study is a single center study, though we have made great effort to consider the diversity of sample sources, we still cannot fully cover the entire fetal population in the country. Thirdly, we did not conduct validation analysis, which is what we need to do in the next step. In the future, we plan to conduct more sample collection, utilize new analytical methods and cross center collaboration to establish more accurate and reliable Chinese fetal growth curves.
As a populous country, China has billions of newborns every year, but we do not have a Chinese fetal growth curve. Our research shows that those other’s growth curves currently used may not necessarily be suitable for our national population, and long-term use of these references can lead to misdiagnosis of fetal dwarfism, which will have serious consequences and significant impact. We suggest establishing a multicenter fetal growth curve standard that is more suitable for the Chinese population, and adopting this standard will greatly reduce the diagnosis of fetal dwarfism.
In conclusion, our study demonstrated that the Hadlock references had an higher rate of overdiagnosis of fetal smallness in the second and third trimester and could lead to serious misdiagnosis for fetal smallness in late gestation, potentially resulting in an unnecessary invasive examination, or unappropriate interventions such induction of labor. We suggest a more suitable standard for Chinese infants In China, a country with a large population, we suggest a more suitable standard for Chinese infants and if it was to beis adopted properly, overdiagnosis of fetal short stature may be greatly reduced.