Ksenia Olisova, MD, MPH. Director of Medical Research, Taiji Clinic, Taipei, Taiwan
Fetal biometry assessment is an integral part of a routine pregnancy ultrasound scan. We can assess fetal size (instant information about the fetal measurements) and fetal growth (how the size changes with gestational age). Although fetal biometry is a conventional tool in obstetric practice, there are multiple inconsistencies in terminology, measurement protocols, and cut-off values for defining small, appropriate, or large for gestational age and fetal growth-restricted fetuses.
First and foremost, why is it crucial to have a standardized approach to fetal biometry measurement? Applying a universal measurement protocol allows for fair comparison and supports better continuity of care. For instance, Taiwan has universal health insurance coverage giving an opportunity for pregnant women to change and pick healthcare providers for prenatal care. Thus, the best pregnancy management must provide consistent and comparable fetal growth assessment.
Second, following the same standards will let to implement a countrywide quality control system. It is advisable to have quantitative and qualitative quality control to supervise the quality of ultrasound biometry. Previous studies have shown that quality control is essential, but such systems are rare and need more attention.
Third, one of the Sustainable Development Goals by The United Nations is to end mortality for newborns and children under the age of 5. But to achieve this goal, we need to have a universal tool for fetal size evaluation. Early detection allows for early intervention and improved pregnancy management, and better peripartum outcomes. Unfortunately, there is an ongoing debate on whether fetal development trajectories differ between populations due to ethnicity and genetics. Even though, the situation is different for child growth evaluation. World Health Organization accepted Child Growth Standards, and they have been applied since 2006 worldwide. The data collected since then allowed us to compare children's growth between and within populations. It became clear that rates of child stunting (when a child's height-for-age is more than two standard deviations below the WHO Child Growth Standards median) are greatly varied around the world. But it was also clear that the main cause for such differences were disparities in socioeconomic status, lack of access to nutrition, health care, and detrimental environmental conditions, and less so due to the ethnic differences. Children in optimal conditions can reach their full growth potential.
As a result, the next step was to build prescriptive international fetal growth and size standards, which required an international collaboration and a uniform methodology. The International Fetal and Newborn Growth Consortium for the 21st Century (INTERGROWTH-21st or IG-21st) is a multidisciplinary team of more than 300 researchers from 18 countries who share one goal - to improve perinatal outcomes, especially for preterm births and poor fetal growth. INTERGROWTH-21st became the most extensive collaborative effort in perinatal research. The team with a coordinative center at Oxford University developed new methodological considerations for building new fetal size and growth charts. The recommendations emphasize the difference between descriptive and prescriptive approaches. The descriptive approach implies how the fetuses were growing at a certain population during a certain period, and as a result, we get reference charts. On the other hand, the prescriptive approach explores how fetuses should grow given optimal conditions and requires strict eligibility criteria. To build fetal growth standards as a result of the prescriptive approach, we need to consider multiple factors affecting fetal growth, such as socio-economic status, environmental, nutritional factors, and access to quality healthcare. The researchers argue that we cannot compare fetal growth to the local reference ranges, as we lose valuable information doing that. For example, if we build a reference chart in India where a problem with low birth weight babies is known, we might collect data about babies not in optimal conditions and who do not reach their growth potential. And if we compare to those reference charts, we will only see 10% of the population as small. Which we can understand is not true; to make fair judgments, we need to compare those babies with growth standards based on a healthy population in optimal conditions, and only, in that case, it will be possible to see the true rates of small babies. As another example, local reference charts in Taiwan do not follow the prescriptive approach, in addition, based on the published data it is impossible to calculate mean and standard deviations, so we cannot calculate Z-scores and centiles. As underlined by the methodological considerations, the ability to calculate Z-scores and centiles is essential when we evaluate fetal growth as appropriate, small or large for gestational age.
IG-21st conducted the Fetal Growth Longitudinal Study to build prescriptive fetal standards. The team tried to minimize all kinds of biases. Data collection was done in 8 countries (Brazil, Oman, India, China, Kenya, Italy, UK, USA), following a standard protocol, using standardized equipment and measurement techniques, and a centralized quality control unit. Only women with optimal health, without socioeconomic hardships, living in favorable environmental conditions, easy access to quality healthcare, and without nutritional deficiencies were included. The data collection period has extended from the first semester until early infancy. The researchers focused on head circumference, biparietal diameter (outer-to-outer), occipitofrontal diameter, femur length, and abdominal circumference. The results of the study were published in 2014 by the Lancet. The authors pointed that the results of head circumference measurements from each center were highly alike. It was similar to the findings based on child growth standards by WHO. If given optimal conditions, fetal growth follows the same patterns around the globe. Despite the effort, there is still no agreement among researchers and health organizations. A number of countries applied IG-21st standards, whereas others continue to follow local reference charts. To provide more data about fetal growth in Taiwan and support findings by IG-21st, our team conducted a study following the IG-21st methodology.
TAIWANBABY is an ongoing research project by Taiji clinic in collaboration with 11 medical centers around the island. Our collaborators include: 三軍總醫院, 宏其婦幼醫院, 臺北醫學大學附設醫院, 臺北市立萬芳醫院, 衛生福利部雙和醫院, 臺北榮民總醫院, 高雄榮民總醫院, 台中榮民總醫院, 中山醫學大學附設醫院, 天主教輔仁大學附設醫院, and 大千綜合醫院. Even though the COVID-19 pandemic disrupted the data collection process, we continue our efforts. We applied similar exclusion and inclusion criteria to recruit healthy women and follow them up from the first trimester until birth. As a result, we are planning to build fetal size and growth standards for the local population. In addition to the biometric measurements done by the IG-21st, we will also provide data about the humerus length and biparietal diameter measured by two methods: outer-to-outer, and outer-to-inner. Following the future data analysis, we will provide tools to calculate Z-scores and centiles in open access. Our main mission is to improve perinatal care in Taiwan. Expectant mothers deserve to receive the best perinatal care to reduce their stress during this challenging time. Fetal biometry is only one tool of a fetal medicine specialist, but it can define the course of pregnancy management and sometimes can provide unnecessary worries or miss valuable clues if applied incorrectly. To avoid that, we need to strive for the best quality of care and continue to learn every day.
We hope that the results of our research will aid local clinicians in their decision-making and add to the growing body of international research about fetal biometry. High standards of perinatal care are the key to supporting maternal well-being and a basis for the healthy start of a new life.
