Foetal growth standards: Does one size fit all?

Abstract

Antenatal ultrasonography to monitor foetal growth and well-being is an essential component of obstetric care. Measurement of foetal anthropometric parameters including head circumference, bi-parietal diameter, abdominal circumference and femur length, and the estimated foetal weight derived from these parameters is used for diagnosing restricted or excessive foetal growth and congenital anomalies, such as, small or large head size and skeletal dysplasias. These diagnoses have major therapeutic implications.Thus, it is quite imperative that the reference data should be accurate and representative of the population for which it is being used. There are two major categories of foetal growth charts—those based on serial foetal measurements by ultrasonography, and those based on measurements at birth plotted against gestational age based on last menstrual period. Many different charts of both categories are currently being used to serve as reference normative data. Recently, Intergrowth-21st Consortium has published international foetal growth standards, based on prospectively collected foetal biometric data. The study has been conducted with highly standardized methodology on healthy, affluent, low-risk pregnant women in 8 countries, including India. For the present paper, we have reviewed the merits and drawbacks of these standards, as well as, several other Indian and international charts. None of the currently available charts come up to our expectations from an ‘ideal’ foetal growth chart. We suggest that for a country of our magnitude and diversity, there is an urgent need to construct our national foetal growth standards based on carefully selected population and using robust techniques and methodology.