Rat pregnancy is short. Most litters arrive 21 to 23 days after mating, so a watch window is a matter of three weeks, not months. Early on there is very little to see. Around day 10 to 14 you may notice a gentle pear shape from above, a slightly wider set to the hips, and a rat who eats more and naps more. Nipples become more visible in the last week. From day 16 or so you can sometimes see movement along her sides while she rests. Do not press or squeeze her belly to feel for babies. Weighing her every couple of days on kitchen scales is a kinder way to track things. A steady climb of a few grams a day in the second half is usually a good sign. If you are unsure, treat her as pregnant. Extra food, extra rest and a quiet cage cost nothing if it turns out to be a false alarm.