Mild left renal pelvictiasis, with a measurement of 4.9mm, in a 25-week-old fetus is not uncommon and may not necessarily indicate any major problems. However, it is important to monitor the condition throughout pregnancy and after birth. Renal pelvictiasis refers to the dilation or enlargement of the renal pelvis, which is the area where urine collects before it flows into the bladder. In most cases, mild cases resolve on their own without causing any long-term issues. However, close monitoring by your healthcare provider is necessary to ensure that there are no complications or further progression of the condition. If there are any concerns about kidney function or other abnormalities, additional tests such as ultrasounds or further imaging may be recommended. After birth, your baby's pediatrician will continue to monitor their kidney health through regular check-ups and follow-up scans if necessary. It's important to remember that every case is unique, so consulting with your healthcare provider is crucial for personalized advice and guidance based on your specific situation.