There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.
From the Research
Fetal Microcephaly and Intrauterine Growth Restriction (IUGR)
- Microcephaly is a condition where the head circumference of a fetus or newborn is significantly smaller than average, and it can be associated with intrauterine growth restriction (IUGR) 1, 2, 3.
- IUGR is a condition where a fetus does not achieve its full growth potential during pregnancy, and it can be diagnosed by estimated fetal weight or abdominal circumference below the 10th percentile on formal ultrasonography 4.
- Studies have shown that microcephaly and IUGR can be related, and that microcephaly in growth-restricted fetuses deserves special attention and separate evaluation as it is an important prognostic factor 1.
- Genetic defects, such as variants of the SASS6 gene, can be an underlying cause of primary microcephaly and fetal growth restriction 2.
- Risk factors for microcephaly in extremely low gestational age newborns include nonwhite race, severe intrauterine growth restriction, delivery for preeclampsia, placental infarction, and being female 3.
- Neuroinflammation can play a role in the progression of brain injury in growth-restricted neonates, and identifying the mediators responsible for alterations in brain development in the IUGR infant is key to prevention and treatment of brain injury in these infants 5.
Diagnosis and Prognosis
- Diagnosing fetal microcephaly can be challenging due to differences in definitions and measurement techniques between fetuses and newborns, and a false positive or false negative diagnosis can have significant consequences 1.
- Combining additional parameters such as a positive family history, associated anomalies, and new measurement parameters can improve prediction in about 50% of cases, and should be part of the prenatal workup 1.
- Advances in imaging modalities and prenatal genetic investigation, along with the emergence of new growth charts, can also improve diagnostic accuracy 1.