What causes hiccups in a 3-week-old?

My baby is 3 weeks old. What causes frequent hiccups in a breastfeeding infant?

Hiccups are caused by a spasm of the diaphragm muscle under the lungs. The diaphragm may contract when it's stretched out by a full stomach or it may just "twitch". Healthy infants hiccup frequently, usually without any distress or discomfort. Interestingly, many pregnant women will feel their infant hiccup, starting in the second trimester. Breastfed infants probably hiccup as frequently as formula-fed infants do. When your baby appears to be uncomfortable with hiccuping, try to relieve the wind in her stomach by burping or repositioning her. If she tends to swallow a lot of air during feeds, you might try repositioning her on the breast so she latches on more securely. Infant hiccups are almost always harmless and rarely cause anything more than some transient discomfort for your baby. However, if the hiccups are associated with poor feeding, weight loss or repeated vomiting, you should contact your baby's GP.