How to determine pregnancy.
Pick her up and look at her nipples. During the first 24 hours after a successful mating, her nipples will become prominent and darker/stronger in color. Some hamsters are starting short time after the mating took place with permanent nest-redecorating behavior. This is normal. Syrian females are coming into "heat" all 4 to 5 days. If she don´t come in heat 5 days after the mating, she is pregnant.
Syrian hamsters have the shortest known gestation-period. Normally she will give birth 16 days after the successful mating, sometimes they need 17 days. If she didn´t give birth until day 18, the babies will not be born alive and healthy.
The cage during pregnancy
Some people are saying, that you should remove the wheel during the pregnancy. Well, i tried this only once. The hamster was permanent gnawing on everything reachable - like she never did before (and after). She was running weird around in her cage, searching for something (probably her wheel). This caused more stress to her than the exercise in her wheel could have done. I put the wheel back into her cage and got my happy hamster back.
Till now no one could name a good reason, why i should remove the wheel. I have never had any problems with it so I would never again remove the wheel.
You should put her cage on a silent place. A noisy place or other disturbances should be avoided. Stress should be unknown to her in general.
Provide additional bedding-material for her nest as much as she take into the nest (tissue without perfume or any additional stuff like aloe etc.).
NEVER use fluffy-type bedding! This stuff can get wrapped around neck and paws, causing strangulations which will result in losing limbs or death. I had this problem myself here, so this is not a tale. Some brands (Hagen, Vitakraft, Fluff) are writing the words "Safe" and "Safe for babies" on the package - they are not safe ! Avoid this stuff or you hammies will have to regret it.
You should continue your normal routine until day 14 of the pregnancy. On this day (not earlier, NEVER later!), clean her cage, but don´t touch her nest ! She will have made it ready for the babies. From now on, your are not permitted to touch the nest or poke your finger (or anything else) inside ! And even if the cage is smelling badly, NEVER try to clean the cage until day 14 after the birth!
The pee-corner should be cleaned every day (change the soiled bedding with new bedding, don´t start to clean the corner with water/soap etc!). If your hamster is using a pottie/hamster-toilett, clean the toilett every other day.
Feeding during pregnancy
In general, you should continue with the normal diet you feed her before. Please do not change the complete diet. Those massive changes will do more harm than goods.
Beginning at the first day of the pregnancy, you should provide additional food. She needs additional protein and calcium. The bones of the babies needs calcium to develop. And this will be taken out of the mothers system. Feeding additional calcium will prevent any damages to the babies and to the mothers system. I feed pregnant and nursing hamsters bread soaked in milk each day fresh. The best protein-source is tofu. You can also use babyfood made for humans, but only plain chicken. Fruit- or veggie-food for human babies doesn´t contain additional protein and is therefor useless.
You should not feed "baby-milk" made for human babies to the pregnant mother on a regular/daily basis. This sort of milk is good for babies, but not for the mother cause it´s really more fattening than doing goods (see Breeding, Problems for self-nursing and fostering).
She doesn´t need your help to give birth - so AVOID disturbing her during the deliverance of the babies. Even if something is obviously going wrong, there is near nothing that could be done by unexperienced persons, so leave it up to her.
She will give birth at anytime during the expected date. Normally this will happen during the late evening or the night. The babies will be born one after another, with approximately 5 to 15 minutes in between. During this procedure, she will be active like nothing special is happening - sometimes one or more babies will be born outside the nest. In that case, she will pick the baby up and carry it into the nest. Some hamsters are stuffing the babies into their pouches - this does not mean, she´s eating the baby! Their mothers pouches are the most secure place for the babies in the whole cage.
The first days
The general rule for you is: Do not touch the nest - do not touch the babies !!!
The first days after giving birth the mother will leave the nest only to drink, to eat or to visit her bathroom. Some hamsters will continue with their normal routine after 2 or 3 days.
I know, it´s hard to wait. But leave her nest UNTOUCHED !