Updated December 16, 2014.
Q. We have a 3-4 week old baby. She was born at 8 lbs 7 oz by cesarian. She went home at 7lbs 9 oz 4 days later. She is now about 10 lbs and seems to breastfeed ok. This week she has become extremely fussy, not sleeping and we noticed when we change her diaper her arms shake like she has tremors. In the hospital they said her shaking was due to low blood sugar because my wife's milk was not coming in and she was not nursing well. Now that she is eating better could her shaking and fussiness still be due to low blood sugar? Are we dealing with seizures? How can we tell? Bryan, Burlington, WI
A.

Babies make a lot of movements that are often mistaken for seizures, including having a quivering chin, trembling hands, and jerky arm movements. Fortunately, these types of movements are usually normal. Babies can have seizures though, so if you baby is doing something that you think might be a seizure, you should discuss it with your Pediatrician.

General ways that you can tell if a movement is normal or a seizure include:

• that the movement always occurs at a certain time, like when you change her diaper. You wouldn't expect a seizure to occur only when you change her diaper, so these shaking movements might be simply because she doesn't like her diaper being changed. Infantile spasms are more likely to occur when a baby is going to sleep or waking up, so that is an exception to a movement being normal even if it occurs at the same time each day.
• whether or not you can stop the shaking or jerking. If an infant's arm is jerking and you can stop it by gently hold her arm, then it probably isn't a seizure. With a seizure, you would expect the jerking to continue as you held her arm.

• that your baby is otherwise healthy and growing and developing normally, which would also go against having seizures. Keep in mind that when a baby first begins having seizures, she may be otherwise fine, but over time, you would expect some other symptoms or problems with her development if she was having frequent seizures or spasms.
• having movements that are bilateral (on both sides of her body), symmetric (for example, both arms do the same thing at the same time), and/or rhythmic, which may be a sign of a seizure.

Keep in mind that some seizure disorders in young children can be rather subtle, like a simple head nod, lip smacking, or starting. So talk to your Pediatrician any time that you suspect your baby has a seizure. It is often helpful to record the suspicious activity with a video camera if you can, and bring the tape for your Pediatrician to view.

Fussy Babies

The fact that she is gaining weight well goes against her having low blood sugar as a cause of her symptoms. Is she having 6 or more wet soaking diapers and 3-4 loose, yellow stools each day? If so, and if she seems satisfied after feeding, then those would all be good signs that she is breastfeeding well.
There are other reasons besides not breastfeeding well to have a fussy baby though. It could be that the mother is eating or drinking something that is disagreeing with her. Common suspects and things a breastfeeding mother might avoid include:

• cow's milk and other dairy products
• caffeine
• chocolate
• certain vegetables, like cabbage, onions, and broccoli
• citrus fruits
• certain medications

If you don't notice a difference in your baby's behavior after stopping these types of foods, slowly add them back in so that mom's diet isn't unnecessarily restricted.
Other conditions that could cause a breastfed baby to be fussy include having an overactive let-down reflex, and timing feedings, so that a baby is getting too much lactose rich foremilk, and not the high fat hindmilk. See our guide to Colic in the Breastfed Baby for more information on these issues.

Colic

Lastly, a fussy baby who is 3-4 weeks old may simply be suffering from colic. Although no one knows the definite cause of colic, babies who are colicky usually have a regular fussy period each day that lasts for several hours. Colic typically begins when a baby is 2-3 weeks old, peaks at about 6 weeks, and is gone once an infant is 3-4 months old.
These books offer tips on helping a fussy or colicky baby and may be helpful for you:

• The Happiest Baby on the Block - The New Way to Calm Crying and Help Your Newborn Baby Sleep Longer
• Calming Your Fussy Baby - The Brazelton Way
• The Fussy Baby Book - Parenting Your High-Need Child From Birth to Age Five
• The Fussy Baby - How to Bring Out the Best in Your High-Need Child
• Your Fussy Baby