·Wrong dates- With good menstrual history this problem is unlikely to arise; however, difficulty may occur in women with irregular menstrual periods or ovulation induction. When in doubt, serial ultrasonic scans with BPD, head circumference and cephalic measurements may resolve the issue.
·IUGR- Fetuses suffering from IUGR are small for dates. IUGR may be symmetrical or asymmetrical. Symmetrical IUGR occurs as a result of severe insult in early pregnancy. The fetus is symmetrically small. There is a proportionate reduction in all body parts. This form of IUGR can be diagnosed on ultrasound if accurate dates are known, preferably by CRL measurement.
·Microcephaly- Microcephaly is associated with a multitude of syndromes, chromosomal anomalies, transpiacental infections and maternal addictions. It may also be inherited in an autosomal recessive manner. Diagnosis can be difficult as microcephaly may not develop until late in pregnancy.