Low birth weight is defined as 2500 grams (5.5 lb). Low birth weight is a concern for medical providers due to the tendency of these infants, described as "premature by weight", to have a higher risk of secondary medical problems. Some research shows that fetal ultrasounds (including Doppler, 3D/4D ultrasound and 2D ultrasound) can have some effects on birth weight and neurodevelopment.[32]