Physical development in newborns

In the first month, your doctor will pay close attention to your baby's increasing weight, length, and head circumference, which is measured around the largest point of the head, usually starting at a point on the forehead.

The average birth weight for babies is around 7.5 lb (3.4 kg), although between 5.5 lb (2.5 kg) and 10 lb (4.5 kg) is considered normal. In general:

• Boys are usually a little heavier than girls.
• First babies are usually lighter than later siblings.
• Large parents generally have large babies, while small parents generally have small babies.

Newborns often lose around 8 oz (226.8 g) in the first 4 to 5 days after birth but regain it by about 10 to 12 days of age. In the first month, the typical newborn gains about 0.7 oz (19.8 g) per day, or about 4 oz (113.4 g) to 8 oz (226.8 g) per week.¹

The average length of full-term babies at birth is 20 in. (50.8 cm), although the normal range is between 18 in. (45.7 cm) and 22 in. (55.9 cm). In the first month, babies typically grow 1 in. (2.5 cm) to 1.5 in. (3.8 cm).

Your baby's head will grow at its fastest rate during the first 4 months after birth than at any other time. This increase is due to rapid brain growth. The average head circumference at birth is about 13.5 in. (34.3 cm). By the end of the first month, this measurement increases to an average of about 14.8 in. (37.6 cm).¹

Many babies look a little less than perfect in the first few days or weeks after birth. Gradually they will gain that cute and healthy baby look. Do not be alarmed if your newborn has:

• An irregularly shaped head, often referred to as the "cone-head." This is most common with babies who are born vaginally (rather than by cesarean section, or C-section). Bruising may also occur. A normal head shape will gradually return by the end of the first week.
• Squinty-looking, bloodshot eyes. This is caused by swelling during labor and delivery. Also, antibiotic eye ointment given in the hospital can make your baby's eyes look gooey or small. Your baby's eyes will start to look larger and brighter within a couple of weeks.
• Downy hair on forehead, cheeks, shoulders, and back. This is especially common in babies who are born earlier than their due date. It will usually go away within a few weeks after birth.
• Swollen breasts or genitals. This occurs in both boys and girls when the mother's hormones pass to the baby during birth. Some babies may even have some milky fluid come out of the nipple. Baby girls may have blood-tinged fluid from their vagina.

Other physical developmental issues to be aware of in your baby's first month include:

• Hair loss. Your baby may lose some or all of the hair that he or she had at birth. This loss is temporary and new hair will replace it. Do not worry if your baby develops bald spots.
• Mild skin conditions. Many newborns develop small pimples on the face. This condition is most common between the first and second month, but you may notice some acne developing in the first few weeks. It may help to wash your baby's clothing, bedding, and other fabric items in gentle laundry soap. Also, wash your baby's face with gentle cleanser once a day.
• Lack of ability to self-regulate temperature. Your baby is not yet able to adjust to heat or cold very efficiently. It is important to keep your baby bundled when it is cold and dressed lightly when it is very warm. Try to keep your home at a stable temperature.

Citations

1. American Academy of Pediatrics (2004). The first month. In SP Shelov, RE Hannemann, eds., Caring For Your Baby And Young Child: Birth to Age 5, 4th ed., chap. 6, pp. 143-176. New York: Bantam.