Hello. A lag of two or more weeks is significant if there is inadequate interval growth and reduced baby weight. After reading your query I would like to rule out restricted growth. But a comparison with previous scan reports and any other test results is required. Also your medical history for infections, diabetes , blood pressure etc is important as these are causative/associated factors for Growth restriction. I would suggest you take up this matter with your doctor especially since she has raised a flag, and discuss her concern about defects. Certain infections/diseases/ medicines do affect the fetus, hence please ask her about this possibility. Many times a 1-2 week lag is seen right from the start, but baby shows proper interval growth- then its nothing to worry. But in your case, I would suggest a followup scan for fetal growth (measurements and ratios must be evaluated), asymmetry of growth, amniotic fluid volume and a Doppler study. Hope this is helpful. Please feel free to write in with more details. Take care.