"abnormally small" is a correct and usable phrase in written English.
You can use it to describe something (or someone) that is significantly smaller than usual or expected. For example, "The size of the baby's head was abnormally small."
More frequent anomalies are anophthalmia (absence of eyes) and microphthalmia (abnormally small eyes), both occasionally the result of abnormal heredity.
The Centers for Disease Control and Prevention CDCC) has confirmed that the Zika virus causes fetal brain abnormalities, including microcephaly, which causes babies to be born with abnormally small heads.
These abnormalities included problems with growth, such as microcephaly (meaning an abnormally small head); problems with the placenta; and lesions in the brain or spine.
Animals that presented abnormalities such as hydrocephaly, failure to thrive, missing limbs and/or were abnormally small (runts) were excluded from the experimental groups.
Lightening may be impossible in women who have an abnormally small pelvis, an oversized fetus, or a fetus lying in an abnormal position.
Samples with abnormally small volumes (less than ∼0.2 mL for 10 full breaths) coupled with abnormal animal behavior during collection were verified for metabolic content.
The arms are abnormally small, even spindly.
It can cause an abnormally small head (microcephaly) and other forms of brain damage.
Children with microcephaly are born with abnormally small heads and suffer severe developmental disorders.
Children with microcephaly are born with abnormally small heads and experience severe, lifelong developmental problems.
Infants with microcephaly have abnormally small heads and their brains do not develop properly.
