What factor could classify a newborn as small for gestational age (SGA)?

A newborn is classified as small for gestational age (SGA) based on their growth in relation to gestational age, typically defined as being below the 10th percentile for weight. One significant factor that can influence fetal growth is the genetic background of the parents. Parental genetics can determine a range of factors, including potential size at birth and growth patterns in the womb. If both parents are smaller in stature or have a history of small births, it is plausible that their offspring will also fall into the SGA category, even in the absence of other adverse factors.

Other factors like infection during pregnancy, maternal age over 35, and poor nutrition in the last trimester can also contribute to a fetus being SGA. However, while these factors often impact growth and development during pregnancy, genetic factors are intrinsic to the individual and inform baseline growth potential. Thus, the genetic background of the parents provides a foundational context for assessing fetal size at birth and is a primary consideration in classifying a newborn as SGA.